diff mbox

[AArch64] Recognize more program breakpoint patterns

Message ID 20191223173432.16955-1-luis.machado@linaro.org
State New
Headers show

Commit Message

Luis Machado Dec. 23, 2019, 5:34 p.m. UTC
It was reported to me that program breakpoints (permanent ones inserted into
the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not
generate visible stops when continuing, and GDB will continue spinning
infinitely.

This happens because GDB, upon hitting one of those program breakpoints, thinks
the SIGTRAP came from a delayed breakpoint hit...

(gdb) x/i $pc
=> 0x4005c0 <problem_function>: brk     #0x90f
(gdb) c
Continuing.
infrun: clear_proceed_status_thread (process 14198)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming process 14198
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14198.14198.0 [process 14198],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: delayed software breakpoint trap, ignoring
infrun: no stepping, continue
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14198.14198.0 [process 14198],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: delayed software breakpoint trap, ignoring
infrun: no stepping, continue
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14198.14198.0 [process 14198],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: delayed software breakpoint trap, ignoring
infrun: no stepping, continue
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14198.14198.0 [process 14198],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: delayed software breakpoint trap, ignoring
infrun: no stepping, continue
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14198.14198.0 [process 14198],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
...

... which is not the case.

If the program breakpoint is one GDB recognizes, then it will stop when it
hits it.

(gdb) x/i $pc
=> 0x4005c0 <problem_function>: brk     #0x0
(gdb) c
Continuing.
infrun: clear_proceed_status_thread (process 14193)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming process 14193
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   14193.14193.0 [process 14193],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: random signal (GDB_SIGNAL_TRAP)
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun:   process 14193 not executing
infrun: stop_all_threads, pass=1, iterations=1
infrun:   process 14193 not executing
infrun: stop_all_threads done

Program received signal SIGTRAP, Trace/breakpoint trap.
problem_function () at brk_0.c:7
7        asm("brk %0\n\t" ::"n"(0x0));
infrun: infrun_async(0)

Otherwise GDB will keep trying to resume the inferior and will keep
seeing the SIGTRAP's, without stopping.

To the user it appears GDB has gone into an infinite loop, interruptible only
by Ctrl-C.

Also, windbg seems to use a different variation of AArch64 breakpoint compared
to GDB. This causes problems when debugging Windows on ARM binaries, when
program breakpoints are being used.

The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)
that tells GDB whether the underlying instruction is a breakpoint instruction
or not.

This is more general than only checking for the instruction GDB uses as
breakpoint.

The existing logic is still preserved for targets that do not implement this
new gdbarch method.

The end result is like so:

(gdb) x/i $pc
=> 0x4005c0 <problem_function>: brk     #0x90f
(gdb) c
Continuing.
infrun: clear_proceed_status_thread (process 16417)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: proceed: resuming process 16417
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   16417.16417.0 [process 16417],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: stop_pc = 0x4005c0
infrun: random signal (GDB_SIGNAL_TRAP)
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun:   process 16417 not executing
infrun: stop_all_threads, pass=1, iterations=1
infrun:   process 16417 not executing
infrun: stop_all_threads done

Program received signal SIGTRAP, Trace/breakpoint trap.
problem_function () at brk.c:7
7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));
infrun: infrun_async(0)

Does this change look ok?

gdb/ChangeLog:

2019-12-23  Luis Machado  <luis.machado@linaro.org>

	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.
	(aarch64_insn_is_breakpoint): New function.
	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.
	* arch-utils.c (default_insn_is_breakpoint): New function.
	* arch-utils.h (default_insn_is_breakpoint): New prototype.
	* breakpoint.c (program_breakpoint_here): Updated to use
	  gdbarch_insn_is_breakpoint.
	Update documentation to clarify behavior.
	* gdbarch.c: Regenerate.
	* gdbarch.h: Regenerate.
	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.

Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc
---
 gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++
 gdb/arch-utils.c   |  7 +++++++
 gdb/arch-utils.h   |  3 +++
 gdb/breakpoint.c   | 19 ++++++++++++++-----
 gdb/gdbarch.c      | 23 +++++++++++++++++++++++
 gdb/gdbarch.h      |  7 +++++++
 gdb/gdbarch.sh     |  4 ++++
 7 files changed, 83 insertions(+), 5 deletions(-)

Comments

Alan Hayward Jan. 9, 2020, 2:52 p.m. UTC | #1
> On 23 Dec 2019, at 17:34, Luis Machado <luis.machado@linaro.org> wrote:

> 

> It was reported to me that program breakpoints (permanent ones inserted into

> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not

> generate visible stops when continuing, and GDB will continue spinning

> infinitely.

> 

> This happens because GDB, upon hitting one of those program breakpoints, thinks

> the SIGTRAP came from a delayed breakpoint hit...

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x90f

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 14198)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 14198

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> ...

> 

> ... which is not the case.

> 

> If the program breakpoint is one GDB recognizes, then it will stop when it

> hits it.

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x0

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 14193)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 14193

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14193.14193.0 [process 14193],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: random signal (GDB_SIGNAL_TRAP)

> infrun: stop_waiting

> infrun: stop_all_threads

> infrun: stop_all_threads, pass=0, iterations=0

> infrun:   process 14193 not executing

> infrun: stop_all_threads, pass=1, iterations=1

> infrun:   process 14193 not executing

> infrun: stop_all_threads done

> 

> Program received signal SIGTRAP, Trace/breakpoint trap.

> problem_function () at brk_0.c:7

> 7        asm("brk %0\n\t" ::"n"(0x0));

> infrun: infrun_async(0)

> 

> Otherwise GDB will keep trying to resume the inferior and will keep

> seeing the SIGTRAP's, without stopping.

> 

> To the user it appears GDB has gone into an infinite loop, interruptible only

> by Ctrl-C.

> 

> Also, windbg seems to use a different variation of AArch64 breakpoint compared

> to GDB. This causes problems when debugging Windows on ARM binaries, when

> program breakpoints are being used.

> 

> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)

> that tells GDB whether the underlying instruction is a breakpoint instruction

> or not.

> 

> This is more general than only checking for the instruction GDB uses as

> breakpoint.

> 

> The existing logic is still preserved for targets that do not implement this

> new gdbarch method.

> 

> The end result is like so:

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x90f

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 16417)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 16417

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   16417.16417.0 [process 16417],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: random signal (GDB_SIGNAL_TRAP)

> infrun: stop_waiting

> infrun: stop_all_threads

> infrun: stop_all_threads, pass=0, iterations=0

> infrun:   process 16417 not executing

> infrun: stop_all_threads, pass=1, iterations=1

> infrun:   process 16417 not executing

> infrun: stop_all_threads done

> 

> Program received signal SIGTRAP, Trace/breakpoint trap.

> problem_function () at brk.c:7

> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));

> infrun: infrun_async(0)

> 

> Does this change look ok?

> 

> gdb/ChangeLog:

> 

> 2019-12-23  Luis Machado  <luis.machado@linaro.org>

> 

> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.

> 	(aarch64_insn_is_breakpoint): New function.

> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.

> 	* arch-utils.c (default_insn_is_breakpoint): New function.

> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.

> 	* breakpoint.c (program_breakpoint_here): Updated to use

> 	  gdbarch_insn_is_breakpoint.

> 	Update documentation to clarify behavior.

> 	* gdbarch.c: Regenerate.

> 	* gdbarch.h: Regenerate.

> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.

> 

> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc

> ---

> gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++

> gdb/arch-utils.c   |  7 +++++++

> gdb/arch-utils.h   |  3 +++

> gdb/breakpoint.c   | 19 ++++++++++++++-----

> gdb/gdbarch.c      | 23 +++++++++++++++++++++++

> gdb/gdbarch.h      |  7 +++++++

> gdb/gdbarch.sh     |  4 ++++

> 7 files changed, 83 insertions(+), 5 deletions(-)

> 


Do you have a test case for this? It could go in the gdb.arch/ directory.
It’d be fairly easy to check all the different brk patterns.


> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c

> index 1d5fb2001d..c69361d4ea 100644

> --- a/gdb/aarch64-tdep.c

> +++ b/gdb/aarch64-tdep.c

> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,

>   return false;

> }

> 

> +#define BRK_INSN_MASK 0xd4200000

> +

> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */

> +

> +static bool

> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,

> +			    const gdb_byte *insn,

> +			    unsigned int insn_size)

> +{

> +  gdb_assert (insn != nullptr);

> +

> +  uint32_t i;

> +

> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,

> +					   gdbarch_byte_order (gdbarch));

> +

> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices

> +     of such instructions with different immediate values.  Different OS' may

> +     use a different variation, but they have the same outcome.  */

> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;

> +}

> +

> /* When arguments must be pushed onto the stack, they go on in reverse

>    order.  The code below implements a FILO (stack) to do this.  */

> 

> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)

>   set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,

> 					   aarch64_execute_dwarf_cfa_vendor_op);

> 

> +  /* Permanent/Program breakpoint handling.  */

> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);

> +

>   /* Add some default predicates.  */

>   frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);

>   dwarf2_append_unwinders (gdbarch);

> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c

> index a1a003f91f..99c9f281be 100644

> --- a/gdb/arch-utils.c

> +++ b/gdb/arch-utils.c

> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)

>   return 0;

> }



Add "/* See arch-utils.h.  */" ...

> 

> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,

> +				 const gdb_byte  *insn,

> +				 unsigned int insn_size)

> +{

> +  return false;


I don’t like that this is just returning false, as it’s not really doing what the function name says.

How about if the function did this:
  return (memcmp (target_mem, bpoint, len) == 0);

Then remove the memcmp from program_breakpoint_here_p.

You’ll probably have to move the call to gdbarch_breakpoint_from_pc into here too.


> +}

> +

> void

> default_skip_permanent_breakpoint (struct regcache *regcache)

> {

> diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h

> index 48ff3bb9a1..77ffe8190c 100644

> --- a/gdb/arch-utils.h

> +++ b/gdb/arch-utils.h

> @@ -227,6 +227,9 @@ extern int default_return_in_first_hidden_param_p (struct gdbarch *,

> extern int default_insn_is_call (struct gdbarch *, CORE_ADDR);

> extern int default_insn_is_ret (struct gdbarch *, CORE_ADDR);

> extern int default_insn_is_jump (struct gdbarch *, CORE_ADDR);


... plus a brief comment here.


> +extern bool default_insn_is_breakpoint (struct gdbarch *gdbarch,

> +					const gdb_byte *insn,

> +					unsigned int insn_size);

> 

> /* Do-nothing version of vsyscall_range.  Returns false.  */

> 

> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c

> index 904abda8db..ffb7f7f8be 100644

> --- a/gdb/breakpoint.c

> +++ b/gdb/breakpoint.c

> @@ -8599,14 +8599,23 @@ program_breakpoint_here_p (struct gdbarch *gdbarch, CORE_ADDR address)

>   target_mem = (gdb_byte *) alloca (len);

> 

>   /* Enable the automatic memory restoration from breakpoints while

> -     we read the memory.  Otherwise we could say about our temporary

> -     breakpoints they are permanent.  */

> +     we read the memory.  Otherwise we may find temporary breakpoints, ones

> +     inserted by GDB, and flag them as permanent breakpoints.  */

>   scoped_restore restore_memory

>     = make_scoped_restore_show_memory_breakpoints (0);

> 

> -  if (target_read_memory (address, target_mem, len) == 0

> -      && memcmp (target_mem, bpoint, len) == 0)

> -    return 1;

> +  if (target_read_memory (address, target_mem, len) == 0)

> +    {

> +      /* Check if this is a breakpoint instruction for this architecture,

> +	 including ones used by GDB. 

> +

> +	 Some architectures have more than one possible breakpoint

> +	 instruction, but GDB does not use all of them.  We should detect those

> +	 as well.  */

> +      if (gdbarch_insn_is_breakpoint (gdbarch, target_mem, len)

> +	  ||  memcmp (target_mem, bpoint, len) == 0)

> +	return 1;

> +    }

> 

>   return 0;

> }

> diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c

> index 59c97da985..9e21ba7eca 100644

> --- a/gdb/gdbarch.c

> +++ b/gdb/gdbarch.c

> @@ -345,6 +345,7 @@ struct gdbarch

>   gdbarch_insn_is_call_ftype *insn_is_call;

>   gdbarch_insn_is_ret_ftype *insn_is_ret;

>   gdbarch_insn_is_jump_ftype *insn_is_jump;

> +  gdbarch_insn_is_breakpoint_ftype *insn_is_breakpoint;

>   gdbarch_auxv_parse_ftype *auxv_parse;

>   gdbarch_print_auxv_entry_ftype *print_auxv_entry;

>   gdbarch_vsyscall_range_ftype *vsyscall_range;

> @@ -464,6 +465,7 @@ gdbarch_alloc (const struct gdbarch_info *info,

>   gdbarch->insn_is_call = default_insn_is_call;

>   gdbarch->insn_is_ret = default_insn_is_ret;

>   gdbarch->insn_is_jump = default_insn_is_jump;

> +  gdbarch->insn_is_breakpoint = default_insn_is_breakpoint;

>   gdbarch->print_auxv_entry = default_print_auxv_entry;

>   gdbarch->vsyscall_range = default_vsyscall_range;

>   gdbarch->infcall_mmap = default_infcall_mmap;

> @@ -708,6 +710,7 @@ verify_gdbarch (struct gdbarch *gdbarch)

>   /* Skip verify of insn_is_call, invalid_p == 0 */

>   /* Skip verify of insn_is_ret, invalid_p == 0 */

>   /* Skip verify of insn_is_jump, invalid_p == 0 */

> +  /* Skip verify of insn_is_breakpoint, invalid_p == 0 */

>   /* Skip verify of auxv_parse, has predicate.  */

>   /* Skip verify of print_auxv_entry, invalid_p == 0 */

>   /* Skip verify of vsyscall_range, invalid_p == 0 */

> @@ -1137,6 +1140,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)

>   fprintf_unfiltered (file,

>                       "gdbarch_dump: inner_than = <%s>\n",

>                       host_address_to_string (gdbarch->inner_than));

> +  fprintf_unfiltered (file,

> +                      "gdbarch_dump: insn_is_breakpoint = <%s>\n",

> +                      host_address_to_string (gdbarch->insn_is_breakpoint));

>   fprintf_unfiltered (file,

>                       "gdbarch_dump: insn_is_call = <%s>\n",

>                       host_address_to_string (gdbarch->insn_is_call));

> @@ -4928,6 +4934,23 @@ set_gdbarch_insn_is_jump (struct gdbarch *gdbarch,

>   gdbarch->insn_is_jump = insn_is_jump;

> }

> 

> +bool

> +gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size)

> +{

> +  gdb_assert (gdbarch != NULL);

> +  gdb_assert (gdbarch->insn_is_breakpoint != NULL);

> +  if (gdbarch_debug >= 2)

> +    fprintf_unfiltered (gdb_stdlog, "gdbarch_insn_is_breakpoint called\n");

> +  return gdbarch->insn_is_breakpoint (gdbarch, insn, insn_size);

> +}

> +

> +void

> +set_gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch,

> +                                gdbarch_insn_is_breakpoint_ftype insn_is_breakpoint)

> +{

> +  gdbarch->insn_is_breakpoint = insn_is_breakpoint;

> +}

> +

> int

> gdbarch_auxv_parse_p (struct gdbarch *gdbarch)

> {

> diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h

> index 78e05ecdcb..d94950b8f2 100644

> --- a/gdb/gdbarch.h

> +++ b/gdb/gdbarch.h

> @@ -1545,6 +1545,13 @@ typedef int (gdbarch_insn_is_jump_ftype) (struct gdbarch *gdbarch, CORE_ADDR add

> extern int gdbarch_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr);

> extern void set_gdbarch_insn_is_jump (struct gdbarch *gdbarch, gdbarch_insn_is_jump_ftype *insn_is_jump);

> 

> +/* Return true if INSN of size INSN_SIZE acts like a permanent breakpoint and

> +   false otherwise. */

> +

> +typedef bool (gdbarch_insn_is_breakpoint_ftype) (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size);

> +extern bool gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size);

> +extern void set_gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, gdbarch_insn_is_breakpoint_ftype *insn_is_breakpoint);

> +

> /* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.

>    Return 0 if *READPTR is already at the end of the buffer.

>    Return -1 if there is insufficient buffer for a whole entry.

> diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh

> index 331eb39278..dbf31ee8ae 100755

> --- a/gdb/gdbarch.sh

> +++ b/gdb/gdbarch.sh

> @@ -1152,6 +1152,10 @@ m;int;insn_is_ret;CORE_ADDR addr;addr;;default_insn_is_ret;;0

> # Return non-zero if the instruction at ADDR is a jump; zero otherwise.

> m;int;insn_is_jump;CORE_ADDR addr;addr;;default_insn_is_jump;;0

> 

> +# Return true if INSN of size INSN_SIZE acts like a permanent breakpoint and

> +# false otherwise.

> +m;bool;insn_is_breakpoint;const gdb_byte *insn, unsigned int insn_size;insn, insn_size;;default_insn_is_breakpoint;;0

> +

> # Read one auxv entry from *READPTR, not reading locations >= ENDPTR.

> # Return 0 if *READPTR is already at the end of the buffer.

> # Return -1 if there is insufficient buffer for a whole entry.

> — 

> 2.17.1

>
Luis Machado Jan. 9, 2020, 3:45 p.m. UTC | #2
On 1/9/20 11:52 AM, Alan Hayward wrote:
> 
> 
>> On 23 Dec 2019, at 17:34, Luis Machado <luis.machado@linaro.org> wrote:
>>
>> It was reported to me that program breakpoints (permanent ones inserted into
>> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not
>> generate visible stops when continuing, and GDB will continue spinning
>> infinitely.
>>
>> This happens because GDB, upon hitting one of those program breakpoints, thinks
>> the SIGTRAP came from a delayed breakpoint hit...
>>
>> (gdb) x/i $pc
>> => 0x4005c0 <problem_function>: brk     #0x90f
>> (gdb) c
>> Continuing.
>> infrun: clear_proceed_status_thread (process 14198)
>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>> infrun: proceed: resuming process 14198
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>> infrun: infrun_async(1)
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14198.14198.0 [process 14198],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: delayed software breakpoint trap, ignoring
>> infrun: no stepping, continue
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14198.14198.0 [process 14198],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: delayed software breakpoint trap, ignoring
>> infrun: no stepping, continue
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14198.14198.0 [process 14198],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: delayed software breakpoint trap, ignoring
>> infrun: no stepping, continue
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14198.14198.0 [process 14198],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: delayed software breakpoint trap, ignoring
>> infrun: no stepping, continue
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14198.14198.0 [process 14198],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> ...
>>
>> ... which is not the case.
>>
>> If the program breakpoint is one GDB recognizes, then it will stop when it
>> hits it.
>>
>> (gdb) x/i $pc
>> => 0x4005c0 <problem_function>: brk     #0x0
>> (gdb) c
>> Continuing.
>> infrun: clear_proceed_status_thread (process 14193)
>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>> infrun: proceed: resuming process 14193
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0
>> infrun: infrun_async(1)
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   14193.14193.0 [process 14193],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: random signal (GDB_SIGNAL_TRAP)
>> infrun: stop_waiting
>> infrun: stop_all_threads
>> infrun: stop_all_threads, pass=0, iterations=0
>> infrun:   process 14193 not executing
>> infrun: stop_all_threads, pass=1, iterations=1
>> infrun:   process 14193 not executing
>> infrun: stop_all_threads done
>>
>> Program received signal SIGTRAP, Trace/breakpoint trap.
>> problem_function () at brk_0.c:7
>> 7        asm("brk %0\n\t" ::"n"(0x0));
>> infrun: infrun_async(0)
>>
>> Otherwise GDB will keep trying to resume the inferior and will keep
>> seeing the SIGTRAP's, without stopping.
>>
>> To the user it appears GDB has gone into an infinite loop, interruptible only
>> by Ctrl-C.
>>
>> Also, windbg seems to use a different variation of AArch64 breakpoint compared
>> to GDB. This causes problems when debugging Windows on ARM binaries, when
>> program breakpoints are being used.
>>
>> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)
>> that tells GDB whether the underlying instruction is a breakpoint instruction
>> or not.
>>
>> This is more general than only checking for the instruction GDB uses as
>> breakpoint.
>>
>> The existing logic is still preserved for targets that do not implement this
>> new gdbarch method.
>>
>> The end result is like so:
>>
>> (gdb) x/i $pc
>> => 0x4005c0 <problem_function>: brk     #0x90f
>> (gdb) c
>> Continuing.
>> infrun: clear_proceed_status_thread (process 16417)
>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>> infrun: proceed: resuming process 16417
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0
>> infrun: infrun_async(1)
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun:   16417.16417.0 [process 16417],
>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>> infrun: stop_pc = 0x4005c0
>> infrun: random signal (GDB_SIGNAL_TRAP)
>> infrun: stop_waiting
>> infrun: stop_all_threads
>> infrun: stop_all_threads, pass=0, iterations=0
>> infrun:   process 16417 not executing
>> infrun: stop_all_threads, pass=1, iterations=1
>> infrun:   process 16417 not executing
>> infrun: stop_all_threads done
>>
>> Program received signal SIGTRAP, Trace/breakpoint trap.
>> problem_function () at brk.c:7
>> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));
>> infrun: infrun_async(0)
>>
>> Does this change look ok?
>>
>> gdb/ChangeLog:
>>
>> 2019-12-23  Luis Machado  <luis.machado@linaro.org>
>>
>> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.
>> 	(aarch64_insn_is_breakpoint): New function.
>> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.
>> 	* arch-utils.c (default_insn_is_breakpoint): New function.
>> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.
>> 	* breakpoint.c (program_breakpoint_here): Updated to use
>> 	  gdbarch_insn_is_breakpoint.
>> 	Update documentation to clarify behavior.
>> 	* gdbarch.c: Regenerate.
>> 	* gdbarch.h: Regenerate.
>> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.
>>
>> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc
>> ---
>> gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++
>> gdb/arch-utils.c   |  7 +++++++
>> gdb/arch-utils.h   |  3 +++
>> gdb/breakpoint.c   | 19 ++++++++++++++-----
>> gdb/gdbarch.c      | 23 +++++++++++++++++++++++
>> gdb/gdbarch.h      |  7 +++++++
>> gdb/gdbarch.sh     |  4 ++++
>> 7 files changed, 83 insertions(+), 5 deletions(-)
>>
> 
> Do you have a test case for this? It could go in the gdb.arch/ directory.
> It’d be fairly easy to check all the different brk patterns.
> 
> 

I'll work on this. I'm thinking we could auto-generate a number of brk 
patterns and verify we can continue and hit each of them.

>> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
>> index 1d5fb2001d..c69361d4ea 100644
>> --- a/gdb/aarch64-tdep.c
>> +++ b/gdb/aarch64-tdep.c
>> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,
>>    return false;
>> }
>>
>> +#define BRK_INSN_MASK 0xd4200000
>> +
>> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */
>> +
>> +static bool
>> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,
>> +			    const gdb_byte *insn,
>> +			    unsigned int insn_size)
>> +{
>> +  gdb_assert (insn != nullptr);
>> +
>> +  uint32_t i;
>> +
>> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,
>> +					   gdbarch_byte_order (gdbarch));
>> +
>> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices
>> +     of such instructions with different immediate values.  Different OS' may
>> +     use a different variation, but they have the same outcome.  */
>> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;
>> +}
>> +
>> /* When arguments must be pushed onto the stack, they go on in reverse
>>     order.  The code below implements a FILO (stack) to do this.  */
>>
>> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>>    set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,
>> 					   aarch64_execute_dwarf_cfa_vendor_op);
>>
>> +  /* Permanent/Program breakpoint handling.  */
>> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);
>> +
>>    /* Add some default predicates.  */
>>    frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);
>>    dwarf2_append_unwinders (gdbarch);
>> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
>> index a1a003f91f..99c9f281be 100644
>> --- a/gdb/arch-utils.c
>> +++ b/gdb/arch-utils.c
>> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)
>>    return 0;
>> }
> 
> 
> Add "/* See arch-utils.h.  */" ...
> 

Fixed.

>>
>> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,
>> +				 const gdb_byte  *insn,
>> +				 unsigned int insn_size)
>> +{
>> +  return false;
> 
> I don’t like that this is just returning false, as it’s not really doing what the function name says.
> 
> How about if the function did this:
>    return (memcmp (target_mem, bpoint, len) == 0);
> 
> Then remove the memcmp from program_breakpoint_here_p.

I agree it would be cleaner, but ...

> 
> You’ll probably have to move the call to gdbarch_breakpoint_from_pc into here too.
> 
> 

... this depends on calling gdbarch_breakpoint_from_pc to fetch bpoint, 
and gdbarch_breakpoint_from_pc requires the address information so it 
can determine the breakpoint kind.

Passing in the address is a bit out of scope for what the function is 
supposed to do (verify if a particular instruction is a breakpoint).

I don't have a strong objection towards passing in the address (or NULL 
if no address) if others are OK with it.

>> +}
>> +
>> void
>> default_skip_permanent_breakpoint (struct regcache *regcache)
>> {
>> diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
>> index 48ff3bb9a1..77ffe8190c 100644
>> --- a/gdb/arch-utils.h
>> +++ b/gdb/arch-utils.h
>> @@ -227,6 +227,9 @@ extern int default_return_in_first_hidden_param_p (struct gdbarch *,
>> extern int default_insn_is_call (struct gdbarch *, CORE_ADDR);
>> extern int default_insn_is_ret (struct gdbarch *, CORE_ADDR);
>> extern int default_insn_is_jump (struct gdbarch *, CORE_ADDR);
> 
> ... plus a brief comment here.
> 
>  >> +extern bool default_insn_is_breakpoint (struct gdbarch *gdbarch,
>> +					const gdb_byte *insn,
>> +					unsigned int insn_size);
>>
>> /* Do-nothing version of vsyscall_range.  Returns false.  */
>>

Fixed as well.
Tankut Baris Aktemur Jan. 9, 2020, 3:59 p.m. UTC | #3
On Monday, December 23, 2019 6:35 PM, Luis Machado wrote:
> 

> It was reported to me that program breakpoints (permanent ones inserted into

> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not

> generate visible stops when continuing, and GDB will continue spinning

> infinitely.

> 

> This happens because GDB, upon hitting one of those program breakpoints, thinks

> the SIGTRAP came from a delayed breakpoint hit...

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x90f

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 14198)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 14198

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: delayed software breakpoint trap, ignoring

> infrun: no stepping, continue

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14198.14198.0 [process 14198],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> ...

> 

> ... which is not the case.

> 

> If the program breakpoint is one GDB recognizes, then it will stop when it

> hits it.

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x0

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 14193)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 14193

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   14193.14193.0 [process 14193],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: random signal (GDB_SIGNAL_TRAP)

> infrun: stop_waiting

> infrun: stop_all_threads

> infrun: stop_all_threads, pass=0, iterations=0

> infrun:   process 14193 not executing

> infrun: stop_all_threads, pass=1, iterations=1

> infrun:   process 14193 not executing

> infrun: stop_all_threads done

> 

> Program received signal SIGTRAP, Trace/breakpoint trap.

> problem_function () at brk_0.c:7

> 7        asm("brk %0\n\t" ::"n"(0x0));

> infrun: infrun_async(0)

> 

> Otherwise GDB will keep trying to resume the inferior and will keep

> seeing the SIGTRAP's, without stopping.

> 

> To the user it appears GDB has gone into an infinite loop, interruptible only

> by Ctrl-C.

> 

> Also, windbg seems to use a different variation of AArch64 breakpoint compared

> to GDB. This causes problems when debugging Windows on ARM binaries, when

> program breakpoints are being used.

> 

> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)

> that tells GDB whether the underlying instruction is a breakpoint instruction

> or not.

> 

> This is more general than only checking for the instruction GDB uses as

> breakpoint.

> 

> The existing logic is still preserved for targets that do not implement this

> new gdbarch method.

> 

> The end result is like so:

> 

> (gdb) x/i $pc

> => 0x4005c0 <problem_function>: brk     #0x90f

> (gdb) c

> Continuing.

> infrun: clear_proceed_status_thread (process 16417)

> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

> infrun: proceed: resuming process 16417

> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0

> infrun: infrun_async(1)

> infrun: prepare_to_wait

> infrun: target_wait (-1.0.0, status) =

> infrun:   16417.16417.0 [process 16417],

> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

> infrun: stop_pc = 0x4005c0

> infrun: random signal (GDB_SIGNAL_TRAP)

> infrun: stop_waiting

> infrun: stop_all_threads

> infrun: stop_all_threads, pass=0, iterations=0

> infrun:   process 16417 not executing

> infrun: stop_all_threads, pass=1, iterations=1

> infrun:   process 16417 not executing

> infrun: stop_all_threads done

> 

> Program received signal SIGTRAP, Trace/breakpoint trap.

> problem_function () at brk.c:7

> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));

> infrun: infrun_async(0)

> 

> Does this change look ok?

> 

> gdb/ChangeLog:

> 

> 2019-12-23  Luis Machado  <luis.machado@linaro.org>

> 

> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.

> 	(aarch64_insn_is_breakpoint): New function.

> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.

> 	* arch-utils.c (default_insn_is_breakpoint): New function.

> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.

> 	* breakpoint.c (program_breakpoint_here): Updated to use

> 	  gdbarch_insn_is_breakpoint.

> 	Update documentation to clarify behavior.

> 	* gdbarch.c: Regenerate.

> 	* gdbarch.h: Regenerate.

> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.

> 

> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc

> ---

>  gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++

>  gdb/arch-utils.c   |  7 +++++++

>  gdb/arch-utils.h   |  3 +++

>  gdb/breakpoint.c   | 19 ++++++++++++++-----

>  gdb/gdbarch.c      | 23 +++++++++++++++++++++++

>  gdb/gdbarch.h      |  7 +++++++

>  gdb/gdbarch.sh     |  4 ++++

>  7 files changed, 83 insertions(+), 5 deletions(-)

> 

> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c

> index 1d5fb2001d..c69361d4ea 100644

> --- a/gdb/aarch64-tdep.c

> +++ b/gdb/aarch64-tdep.c

> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,

>    return false;

>  }

> 

> +#define BRK_INSN_MASK 0xd4200000


I have a general question here.  Given that GDB is using C++11, would it
make more sense to have this as

  static constexpr uint32_t BRK_INSN_MASK = 0xd4200000;

for more type-safety for the uses of this #define?

> +

> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */

> +

> +static bool

> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,

> +			    const gdb_byte *insn,

> +			    unsigned int insn_size)

> +{

> +  gdb_assert (insn != nullptr);

> +

> +  uint32_t i;

> +

> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,

> +					   gdbarch_byte_order (gdbarch));


The declaration and the definition can be combined.

> +

> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices

> +     of such instructions with different immediate values.  Different OS' may

> +     use a different variation, but they have the same outcome.  */

> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;

> +}

> +

>  /* When arguments must be pushed onto the stack, they go on in reverse

>     order.  The code below implements a FILO (stack) to do this.  */

> 

> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)

>    set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,

>  					   aarch64_execute_dwarf_cfa_vendor_op);

> 

> +  /* Permanent/Program breakpoint handling.  */

> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);

> +

>    /* Add some default predicates.  */

>    frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);

>    dwarf2_append_unwinders (gdbarch);

> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c

> index a1a003f91f..99c9f281be 100644

> --- a/gdb/arch-utils.c

> +++ b/gdb/arch-utils.c

> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)

>    return 0;

>  }

> 

> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,


Function name shall start at column 0.

Regards,
-Baris

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Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Christin Eisenschmid, Gary Kershaw
Chairperson of the Supervisory Board: Nicole Lau
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Commercial Register: Amtsgericht Muenchen HRB 186928
Alan Hayward Jan. 9, 2020, 4:25 p.m. UTC | #4
> On 9 Jan 2020, at 15:45, Luis Machado <luis.machado@linaro.org> wrote:

> 

> On 1/9/20 11:52 AM, Alan Hayward wrote:

>>> On 23 Dec 2019, at 17:34, Luis Machado <luis.machado@linaro.org> wrote:

>>> 

>>> It was reported to me that program breakpoints (permanent ones inserted into

>>> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not

>>> generate visible stops when continuing, and GDB will continue spinning

>>> infinitely.

>>> 

>>> This happens because GDB, upon hitting one of those program breakpoints, thinks

>>> the SIGTRAP came from a delayed breakpoint hit...

>>> 

>>> (gdb) x/i $pc

>>> => 0x4005c0 <problem_function>: brk     #0x90f

>>> (gdb) c

>>> Continuing.

>>> infrun: clear_proceed_status_thread (process 14198)

>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>> infrun: proceed: resuming process 14198

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>> infrun: infrun_async(1)

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14198.14198.0 [process 14198],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: delayed software breakpoint trap, ignoring

>>> infrun: no stepping, continue

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14198.14198.0 [process 14198],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: delayed software breakpoint trap, ignoring

>>> infrun: no stepping, continue

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14198.14198.0 [process 14198],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: delayed software breakpoint trap, ignoring

>>> infrun: no stepping, continue

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14198.14198.0 [process 14198],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: delayed software breakpoint trap, ignoring

>>> infrun: no stepping, continue

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14198.14198.0 [process 14198],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> ...

>>> 

>>> ... which is not the case.

>>> 

>>> If the program breakpoint is one GDB recognizes, then it will stop when it

>>> hits it.

>>> 

>>> (gdb) x/i $pc

>>> => 0x4005c0 <problem_function>: brk     #0x0

>>> (gdb) c

>>> Continuing.

>>> infrun: clear_proceed_status_thread (process 14193)

>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>> infrun: proceed: resuming process 14193

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0

>>> infrun: infrun_async(1)

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   14193.14193.0 [process 14193],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: random signal (GDB_SIGNAL_TRAP)

>>> infrun: stop_waiting

>>> infrun: stop_all_threads

>>> infrun: stop_all_threads, pass=0, iterations=0

>>> infrun:   process 14193 not executing

>>> infrun: stop_all_threads, pass=1, iterations=1

>>> infrun:   process 14193 not executing

>>> infrun: stop_all_threads done

>>> 

>>> Program received signal SIGTRAP, Trace/breakpoint trap.

>>> problem_function () at brk_0.c:7

>>> 7        asm("brk %0\n\t" ::"n"(0x0));

>>> infrun: infrun_async(0)

>>> 

>>> Otherwise GDB will keep trying to resume the inferior and will keep

>>> seeing the SIGTRAP's, without stopping.

>>> 

>>> To the user it appears GDB has gone into an infinite loop, interruptible only

>>> by Ctrl-C.

>>> 

>>> Also, windbg seems to use a different variation of AArch64 breakpoint compared

>>> to GDB. This causes problems when debugging Windows on ARM binaries, when

>>> program breakpoints are being used.

>>> 

>>> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)

>>> that tells GDB whether the underlying instruction is a breakpoint instruction

>>> or not.

>>> 

>>> This is more general than only checking for the instruction GDB uses as

>>> breakpoint.

>>> 

>>> The existing logic is still preserved for targets that do not implement this

>>> new gdbarch method.

>>> 

>>> The end result is like so:

>>> 

>>> (gdb) x/i $pc

>>> => 0x4005c0 <problem_function>: brk     #0x90f

>>> (gdb) c

>>> Continuing.

>>> infrun: clear_proceed_status_thread (process 16417)

>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>> infrun: proceed: resuming process 16417

>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0

>>> infrun: infrun_async(1)

>>> infrun: prepare_to_wait

>>> infrun: target_wait (-1.0.0, status) =

>>> infrun:   16417.16417.0 [process 16417],

>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>> infrun: stop_pc = 0x4005c0

>>> infrun: random signal (GDB_SIGNAL_TRAP)

>>> infrun: stop_waiting

>>> infrun: stop_all_threads

>>> infrun: stop_all_threads, pass=0, iterations=0

>>> infrun:   process 16417 not executing

>>> infrun: stop_all_threads, pass=1, iterations=1

>>> infrun:   process 16417 not executing

>>> infrun: stop_all_threads done

>>> 

>>> Program received signal SIGTRAP, Trace/breakpoint trap.

>>> problem_function () at brk.c:7

>>> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));

>>> infrun: infrun_async(0)

>>> 

>>> Does this change look ok?

>>> 

>>> gdb/ChangeLog:

>>> 

>>> 2019-12-23  Luis Machado  <luis.machado@linaro.org>

>>> 

>>> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.

>>> 	(aarch64_insn_is_breakpoint): New function.

>>> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.

>>> 	* arch-utils.c (default_insn_is_breakpoint): New function.

>>> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.

>>> 	* breakpoint.c (program_breakpoint_here): Updated to use

>>> 	  gdbarch_insn_is_breakpoint.

>>> 	Update documentation to clarify behavior.

>>> 	* gdbarch.c: Regenerate.

>>> 	* gdbarch.h: Regenerate.

>>> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.

>>> 

>>> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc

>>> ---

>>> gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++

>>> gdb/arch-utils.c   |  7 +++++++

>>> gdb/arch-utils.h   |  3 +++

>>> gdb/breakpoint.c   | 19 ++++++++++++++-----

>>> gdb/gdbarch.c      | 23 +++++++++++++++++++++++

>>> gdb/gdbarch.h      |  7 +++++++

>>> gdb/gdbarch.sh     |  4 ++++

>>> 7 files changed, 83 insertions(+), 5 deletions(-)

>>> 

>> Do you have a test case for this? It could go in the gdb.arch/ directory.

>> It’d be fairly easy to check all the different brk patterns.

> 

> I'll work on this. I'm thinking we could auto-generate a number of brk patterns and verify we can continue and hit each of them.

> 

>>> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c

>>> index 1d5fb2001d..c69361d4ea 100644

>>> --- a/gdb/aarch64-tdep.c

>>> +++ b/gdb/aarch64-tdep.c

>>> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,

>>>   return false;

>>> }

>>> 

>>> +#define BRK_INSN_MASK 0xd4200000

>>> +

>>> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */

>>> +

>>> +static bool

>>> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,

>>> +			    const gdb_byte *insn,

>>> +			    unsigned int insn_size)

>>> +{

>>> +  gdb_assert (insn != nullptr);

>>> +

>>> +  uint32_t i;

>>> +

>>> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,

>>> +					   gdbarch_byte_order (gdbarch));

>>> +

>>> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices

>>> +     of such instructions with different immediate values.  Different OS' may

>>> +     use a different variation, but they have the same outcome.  */

>>> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;

>>> +}

>>> +

>>> /* When arguments must be pushed onto the stack, they go on in reverse

>>>    order.  The code below implements a FILO (stack) to do this.  */

>>> 

>>> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)

>>>   set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,

>>> 					   aarch64_execute_dwarf_cfa_vendor_op);

>>> 

>>> +  /* Permanent/Program breakpoint handling.  */

>>> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);

>>> +

>>>   /* Add some default predicates.  */

>>>   frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);

>>>   dwarf2_append_unwinders (gdbarch);

>>> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c

>>> index a1a003f91f..99c9f281be 100644

>>> --- a/gdb/arch-utils.c

>>> +++ b/gdb/arch-utils.c

>>> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)

>>>   return 0;

>>> }

>> Add "/* See arch-utils.h.  */" ...

> 

> Fixed.

> 

>>> 

>>> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,

>>> +				 const gdb_byte  *insn,

>>> +				 unsigned int insn_size)

>>> +{

>>> +  return false;

>> I don’t like that this is just returning false, as it’s not really doing what the function name says.

>> How about if the function did this:

>>   return (memcmp (target_mem, bpoint, len) == 0);

>> Then remove the memcmp from program_breakpoint_here_p.

> 

> I agree it would be cleaner, but ...

> 

>> You’ll probably have to move the call to gdbarch_breakpoint_from_pc into here too.

> 

> ... this depends on calling gdbarch_breakpoint_from_pc to fetch bpoint, and gdbarch_breakpoint_from_pc requires the address information so it can determine the breakpoint kind.

> 

> Passing in the address is a bit out of scope for what the function is supposed to do (verify if a particular instruction is a breakpoint).

> 

> I don't have a strong objection towards passing in the address (or NULL if no address) if others are OK with it.


How about replacing program_breakpoint_here_p with 
gdbarch_program_breakpoint_here_p(struct gdbarch *gdbarch, CORE_ADDR address) ?

default_program_breakpoint_here_p would be an exact copy of the existing program_breakpoint_here_p.

aarch64_program_breakpoint_here_p would do the copy to memory then the same as aarch64_insn_is_breakpoint.


> 

>>> +}

>>> +

>>> void

>>> default_skip_permanent_breakpoint (struct regcache *regcache)

>>> {

>>> diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h

>>> index 48ff3bb9a1..77ffe8190c 100644

>>> --- a/gdb/arch-utils.h

>>> +++ b/gdb/arch-utils.h

>>> @@ -227,6 +227,9 @@ extern int default_return_in_first_hidden_param_p (struct gdbarch *,

>>> extern int default_insn_is_call (struct gdbarch *, CORE_ADDR);

>>> extern int default_insn_is_ret (struct gdbarch *, CORE_ADDR);

>>> extern int default_insn_is_jump (struct gdbarch *, CORE_ADDR);

>> ... plus a brief comment here.

>> >> +extern bool default_insn_is_breakpoint (struct gdbarch *gdbarch,

>>> +					const gdb_byte *insn,

>>> +					unsigned int insn_size);

>>> 

>>> /* Do-nothing version of vsyscall_range.  Returns false.  */

>>> 

> 

> Fixed as well.
Luis Machado Jan. 10, 2020, 2:58 p.m. UTC | #5
On 1/9/20 1:25 PM, Alan Hayward wrote:
> 
> 
>> On 9 Jan 2020, at 15:45, Luis Machado <luis.machado@linaro.org> wrote:
>>
>> On 1/9/20 11:52 AM, Alan Hayward wrote:
>>>> On 23 Dec 2019, at 17:34, Luis Machado <luis.machado@linaro.org> wrote:
>>>>
>>>> It was reported to me that program breakpoints (permanent ones inserted into
>>>> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not
>>>> generate visible stops when continuing, and GDB will continue spinning
>>>> infinitely.
>>>>
>>>> This happens because GDB, upon hitting one of those program breakpoints, thinks
>>>> the SIGTRAP came from a delayed breakpoint hit...
>>>>
>>>> (gdb) x/i $pc
>>>> => 0x4005c0 <problem_function>: brk     #0x90f
>>>> (gdb) c
>>>> Continuing.
>>>> infrun: clear_proceed_status_thread (process 14198)
>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>>>> infrun: proceed: resuming process 14198
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>>>> infrun: infrun_async(1)
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14198.14198.0 [process 14198],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: delayed software breakpoint trap, ignoring
>>>> infrun: no stepping, continue
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14198.14198.0 [process 14198],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: delayed software breakpoint trap, ignoring
>>>> infrun: no stepping, continue
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14198.14198.0 [process 14198],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: delayed software breakpoint trap, ignoring
>>>> infrun: no stepping, continue
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14198.14198.0 [process 14198],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: delayed software breakpoint trap, ignoring
>>>> infrun: no stepping, continue
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14198.14198.0 [process 14198],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> ...
>>>>
>>>> ... which is not the case.
>>>>
>>>> If the program breakpoint is one GDB recognizes, then it will stop when it
>>>> hits it.
>>>>
>>>> (gdb) x/i $pc
>>>> => 0x4005c0 <problem_function>: brk     #0x0
>>>> (gdb) c
>>>> Continuing.
>>>> infrun: clear_proceed_status_thread (process 14193)
>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>>>> infrun: proceed: resuming process 14193
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0
>>>> infrun: infrun_async(1)
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   14193.14193.0 [process 14193],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: random signal (GDB_SIGNAL_TRAP)
>>>> infrun: stop_waiting
>>>> infrun: stop_all_threads
>>>> infrun: stop_all_threads, pass=0, iterations=0
>>>> infrun:   process 14193 not executing
>>>> infrun: stop_all_threads, pass=1, iterations=1
>>>> infrun:   process 14193 not executing
>>>> infrun: stop_all_threads done
>>>>
>>>> Program received signal SIGTRAP, Trace/breakpoint trap.
>>>> problem_function () at brk_0.c:7
>>>> 7        asm("brk %0\n\t" ::"n"(0x0));
>>>> infrun: infrun_async(0)
>>>>
>>>> Otherwise GDB will keep trying to resume the inferior and will keep
>>>> seeing the SIGTRAP's, without stopping.
>>>>
>>>> To the user it appears GDB has gone into an infinite loop, interruptible only
>>>> by Ctrl-C.
>>>>
>>>> Also, windbg seems to use a different variation of AArch64 breakpoint compared
>>>> to GDB. This causes problems when debugging Windows on ARM binaries, when
>>>> program breakpoints are being used.
>>>>
>>>> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)
>>>> that tells GDB whether the underlying instruction is a breakpoint instruction
>>>> or not.
>>>>
>>>> This is more general than only checking for the instruction GDB uses as
>>>> breakpoint.
>>>>
>>>> The existing logic is still preserved for targets that do not implement this
>>>> new gdbarch method.
>>>>
>>>> The end result is like so:
>>>>
>>>> (gdb) x/i $pc
>>>> => 0x4005c0 <problem_function>: brk     #0x90f
>>>> (gdb) c
>>>> Continuing.
>>>> infrun: clear_proceed_status_thread (process 16417)
>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
>>>> infrun: proceed: resuming process 16417
>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0
>>>> infrun: infrun_async(1)
>>>> infrun: prepare_to_wait
>>>> infrun: target_wait (-1.0.0, status) =
>>>> infrun:   16417.16417.0 [process 16417],
>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP
>>>> infrun: stop_pc = 0x4005c0
>>>> infrun: random signal (GDB_SIGNAL_TRAP)
>>>> infrun: stop_waiting
>>>> infrun: stop_all_threads
>>>> infrun: stop_all_threads, pass=0, iterations=0
>>>> infrun:   process 16417 not executing
>>>> infrun: stop_all_threads, pass=1, iterations=1
>>>> infrun:   process 16417 not executing
>>>> infrun: stop_all_threads done
>>>>
>>>> Program received signal SIGTRAP, Trace/breakpoint trap.
>>>> problem_function () at brk.c:7
>>>> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));
>>>> infrun: infrun_async(0)
>>>>
>>>> Does this change look ok?
>>>>
>>>> gdb/ChangeLog:
>>>>
>>>> 2019-12-23  Luis Machado  <luis.machado@linaro.org>
>>>>
>>>> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.
>>>> 	(aarch64_insn_is_breakpoint): New function.
>>>> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.
>>>> 	* arch-utils.c (default_insn_is_breakpoint): New function.
>>>> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.
>>>> 	* breakpoint.c (program_breakpoint_here): Updated to use
>>>> 	  gdbarch_insn_is_breakpoint.
>>>> 	Update documentation to clarify behavior.
>>>> 	* gdbarch.c: Regenerate.
>>>> 	* gdbarch.h: Regenerate.
>>>> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.
>>>>
>>>> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc
>>>> ---
>>>> gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++
>>>> gdb/arch-utils.c   |  7 +++++++
>>>> gdb/arch-utils.h   |  3 +++
>>>> gdb/breakpoint.c   | 19 ++++++++++++++-----
>>>> gdb/gdbarch.c      | 23 +++++++++++++++++++++++
>>>> gdb/gdbarch.h      |  7 +++++++
>>>> gdb/gdbarch.sh     |  4 ++++
>>>> 7 files changed, 83 insertions(+), 5 deletions(-)
>>>>
>>> Do you have a test case for this? It could go in the gdb.arch/ directory.
>>> It’d be fairly easy to check all the different brk patterns.
>>
>> I'll work on this. I'm thinking we could auto-generate a number of brk patterns and verify we can continue and hit each of them.
>>
>>>> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
>>>> index 1d5fb2001d..c69361d4ea 100644
>>>> --- a/gdb/aarch64-tdep.c
>>>> +++ b/gdb/aarch64-tdep.c
>>>> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,
>>>>    return false;
>>>> }
>>>>
>>>> +#define BRK_INSN_MASK 0xd4200000
>>>> +
>>>> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */
>>>> +
>>>> +static bool
>>>> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,
>>>> +			    const gdb_byte *insn,
>>>> +			    unsigned int insn_size)
>>>> +{
>>>> +  gdb_assert (insn != nullptr);
>>>> +
>>>> +  uint32_t i;
>>>> +
>>>> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,
>>>> +					   gdbarch_byte_order (gdbarch));
>>>> +
>>>> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices
>>>> +     of such instructions with different immediate values.  Different OS' may
>>>> +     use a different variation, but they have the same outcome.  */
>>>> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;
>>>> +}
>>>> +
>>>> /* When arguments must be pushed onto the stack, they go on in reverse
>>>>     order.  The code below implements a FILO (stack) to do this.  */
>>>>
>>>> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>>>>    set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,
>>>> 					   aarch64_execute_dwarf_cfa_vendor_op);
>>>>
>>>> +  /* Permanent/Program breakpoint handling.  */
>>>> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);
>>>> +
>>>>    /* Add some default predicates.  */
>>>>    frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);
>>>>    dwarf2_append_unwinders (gdbarch);
>>>> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
>>>> index a1a003f91f..99c9f281be 100644
>>>> --- a/gdb/arch-utils.c
>>>> +++ b/gdb/arch-utils.c
>>>> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)
>>>>    return 0;
>>>> }
>>> Add "/* See arch-utils.h.  */" ...
>>
>> Fixed.
>>
>>>>
>>>> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,
>>>> +				 const gdb_byte  *insn,
>>>> +				 unsigned int insn_size)
>>>> +{
>>>> +  return false;
>>> I don’t like that this is just returning false, as it’s not really doing what the function name says.
>>> How about if the function did this:
>>>    return (memcmp (target_mem, bpoint, len) == 0);
>>> Then remove the memcmp from program_breakpoint_here_p.
>>
>> I agree it would be cleaner, but ...
>>
>>> You’ll probably have to move the call to gdbarch_breakpoint_from_pc into here too.
>>
>> ... this depends on calling gdbarch_breakpoint_from_pc to fetch bpoint, and gdbarch_breakpoint_from_pc requires the address information so it can determine the breakpoint kind.
>>
>> Passing in the address is a bit out of scope for what the function is supposed to do (verify if a particular instruction is a breakpoint).
>>
>> I don't have a strong objection towards passing in the address (or NULL if no address) if others are OK with it.
> 
> How about replacing program_breakpoint_here_p with
> gdbarch_program_breakpoint_here_p(struct gdbarch *gdbarch, CORE_ADDR address) ?
> 
> default_program_breakpoint_here_p would be an exact copy of the existing program_breakpoint_here_p.
> 
> aarch64_program_breakpoint_here_p would do the copy to memory then the same as aarch64_insn_is_breakpoint.

It sounds interesting at first, but i'm not sure about it. We'll save a 
memory comparison but will duplicate the code to 
gdbarch_breakpoint_from_pc to every arch that sets its own 
gdbarch_program_breakpoint_here_p.

At least the old function dealt with just arch-specific bits, whereas 
the <arch>_program_breakpoint_here_p implementation will need to do a 
generic check + generic memory read as well, then do the arch-specific 
checks.

Thoughts?
Alan Hayward Jan. 10, 2020, 4:53 p.m. UTC | #6
> On 10 Jan 2020, at 14:58, Luis Machado <luis.machado@linaro.org> wrote:

> 

> 

> 

> On 1/9/20 1:25 PM, Alan Hayward wrote:

>>> On 9 Jan 2020, at 15:45, Luis Machado <luis.machado@linaro.org> wrote:

>>> 

>>> On 1/9/20 11:52 AM, Alan Hayward wrote:

>>>>> On 23 Dec 2019, at 17:34, Luis Machado <luis.machado@linaro.org> wrote:

>>>>> 

>>>>> It was reported to me that program breakpoints (permanent ones inserted into

>>>>> the code itself) other than the one GDB uses for AArch64 (0xd4200000) do not

>>>>> generate visible stops when continuing, and GDB will continue spinning

>>>>> infinitely.

>>>>> 

>>>>> This happens because GDB, upon hitting one of those program breakpoints, thinks

>>>>> the SIGTRAP came from a delayed breakpoint hit...

>>>>> 

>>>>> (gdb) x/i $pc

>>>>> => 0x4005c0 <problem_function>: brk     #0x90f

>>>>> (gdb) c

>>>>> Continuing.

>>>>> infrun: clear_proceed_status_thread (process 14198)

>>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>>>> infrun: proceed: resuming process 14198

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>>>> infrun: infrun_async(1)

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14198.14198.0 [process 14198],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: delayed software breakpoint trap, ignoring

>>>>> infrun: no stepping, continue

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14198.14198.0 [process 14198],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: delayed software breakpoint trap, ignoring

>>>>> infrun: no stepping, continue

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14198.14198.0 [process 14198],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: delayed software breakpoint trap, ignoring

>>>>> infrun: no stepping, continue

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14198.14198.0 [process 14198],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: delayed software breakpoint trap, ignoring

>>>>> infrun: no stepping, continue

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14198] at 0x4005c0

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14198.14198.0 [process 14198],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> ...

>>>>> 

>>>>> ... which is not the case.

>>>>> 

>>>>> If the program breakpoint is one GDB recognizes, then it will stop when it

>>>>> hits it.

>>>>> 

>>>>> (gdb) x/i $pc

>>>>> => 0x4005c0 <problem_function>: brk     #0x0

>>>>> (gdb) c

>>>>> Continuing.

>>>>> infrun: clear_proceed_status_thread (process 14193)

>>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>>>> infrun: proceed: resuming process 14193

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 14193] at 0x4005c0

>>>>> infrun: infrun_async(1)

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   14193.14193.0 [process 14193],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: random signal (GDB_SIGNAL_TRAP)

>>>>> infrun: stop_waiting

>>>>> infrun: stop_all_threads

>>>>> infrun: stop_all_threads, pass=0, iterations=0

>>>>> infrun:   process 14193 not executing

>>>>> infrun: stop_all_threads, pass=1, iterations=1

>>>>> infrun:   process 14193 not executing

>>>>> infrun: stop_all_threads done

>>>>> 

>>>>> Program received signal SIGTRAP, Trace/breakpoint trap.

>>>>> problem_function () at brk_0.c:7

>>>>> 7        asm("brk %0\n\t" ::"n"(0x0));

>>>>> infrun: infrun_async(0)

>>>>> 

>>>>> Otherwise GDB will keep trying to resume the inferior and will keep

>>>>> seeing the SIGTRAP's, without stopping.

>>>>> 

>>>>> To the user it appears GDB has gone into an infinite loop, interruptible only

>>>>> by Ctrl-C.

>>>>> 

>>>>> Also, windbg seems to use a different variation of AArch64 breakpoint compared

>>>>> to GDB. This causes problems when debugging Windows on ARM binaries, when

>>>>> program breakpoints are being used.

>>>>> 

>>>>> The proposed patch creates a new gdbarch method (gdbarch_insn_is_breakpoint)

>>>>> that tells GDB whether the underlying instruction is a breakpoint instruction

>>>>> or not.

>>>>> 

>>>>> This is more general than only checking for the instruction GDB uses as

>>>>> breakpoint.

>>>>> 

>>>>> The existing logic is still preserved for targets that do not implement this

>>>>> new gdbarch method.

>>>>> 

>>>>> The end result is like so:

>>>>> 

>>>>> (gdb) x/i $pc

>>>>> => 0x4005c0 <problem_function>: brk     #0x90f

>>>>> (gdb) c

>>>>> Continuing.

>>>>> infrun: clear_proceed_status_thread (process 16417)

>>>>> infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)

>>>>> infrun: proceed: resuming process 16417

>>>>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 16417] at 0x4005c0

>>>>> infrun: infrun_async(1)

>>>>> infrun: prepare_to_wait

>>>>> infrun: target_wait (-1.0.0, status) =

>>>>> infrun:   16417.16417.0 [process 16417],

>>>>> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: handle_inferior_event status->kind = stopped, signal = GDB_SIGNAL_TRAP

>>>>> infrun: stop_pc = 0x4005c0

>>>>> infrun: random signal (GDB_SIGNAL_TRAP)

>>>>> infrun: stop_waiting

>>>>> infrun: stop_all_threads

>>>>> infrun: stop_all_threads, pass=0, iterations=0

>>>>> infrun:   process 16417 not executing

>>>>> infrun: stop_all_threads, pass=1, iterations=1

>>>>> infrun:   process 16417 not executing

>>>>> infrun: stop_all_threads done

>>>>> 

>>>>> Program received signal SIGTRAP, Trace/breakpoint trap.

>>>>> problem_function () at brk.c:7

>>>>> 7        asm("brk %0\n\t" ::"n"(0x900 + 0xf));

>>>>> infrun: infrun_async(0)

>>>>> 

>>>>> Does this change look ok?

>>>>> 

>>>>> gdb/ChangeLog:

>>>>> 

>>>>> 2019-12-23  Luis Machado  <luis.machado@linaro.org>

>>>>> 

>>>>> 	* aarch64-tdep.c (BRK_INSN_MASK): Define to 0xd4200000.

>>>>> 	(aarch64_insn_is_breakpoint): New function.

>>>>> 	(aarch64_gdbarch_init): Set gdbarch_insn_is_breakpoint hook.

>>>>> 	* arch-utils.c (default_insn_is_breakpoint): New function.

>>>>> 	* arch-utils.h (default_insn_is_breakpoint): New prototype.

>>>>> 	* breakpoint.c (program_breakpoint_here): Updated to use

>>>>> 	  gdbarch_insn_is_breakpoint.

>>>>> 	Update documentation to clarify behavior.

>>>>> 	* gdbarch.c: Regenerate.

>>>>> 	* gdbarch.h: Regenerate.

>>>>> 	* gdbarch.sh (gdbarch_insn_is_breakpoint): New method.

>>>>> 

>>>>> Change-Id: I96eb27151442f435560a58c87eac48b0f68432bc

>>>>> ---

>>>>> gdb/aarch64-tdep.c | 25 +++++++++++++++++++++++++

>>>>> gdb/arch-utils.c   |  7 +++++++

>>>>> gdb/arch-utils.h   |  3 +++

>>>>> gdb/breakpoint.c   | 19 ++++++++++++++-----

>>>>> gdb/gdbarch.c      | 23 +++++++++++++++++++++++

>>>>> gdb/gdbarch.h      |  7 +++++++

>>>>> gdb/gdbarch.sh     |  4 ++++

>>>>> 7 files changed, 83 insertions(+), 5 deletions(-)

>>>>> 

>>>> Do you have a test case for this? It could go in the gdb.arch/ directory.

>>>> It’d be fairly easy to check all the different brk patterns.

>>> 

>>> I'll work on this. I'm thinking we could auto-generate a number of brk patterns and verify we can continue and hit each of them.

>>> 

>>>>> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c

>>>>> index 1d5fb2001d..c69361d4ea 100644

>>>>> --- a/gdb/aarch64-tdep.c

>>>>> +++ b/gdb/aarch64-tdep.c

>>>>> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,

>>>>>   return false;

>>>>> }

>>>>> 

>>>>> +#define BRK_INSN_MASK 0xd4200000

>>>>> +

>>>>> +/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */

>>>>> +

>>>>> +static bool

>>>>> +aarch64_insn_is_breakpoint (gdbarch *gdbarch,

>>>>> +			    const gdb_byte *insn,

>>>>> +			    unsigned int insn_size)

>>>>> +{

>>>>> +  gdb_assert (insn != nullptr);

>>>>> +

>>>>> +  uint32_t i;

>>>>> +

>>>>> +  i = (uint32_t) extract_unsigned_integer (insn, insn_size,

>>>>> +					   gdbarch_byte_order (gdbarch));

>>>>> +

>>>>> +  /* Check if INSN is a BRK instruction pattern.  There are multiple choices

>>>>> +     of such instructions with different immediate values.  Different OS' may

>>>>> +     use a different variation, but they have the same outcome.  */

>>>>> +  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;

>>>>> +}

>>>>> +

>>>>> /* When arguments must be pushed onto the stack, they go on in reverse

>>>>>    order.  The code below implements a FILO (stack) to do this.  */

>>>>> 

>>>>> @@ -3357,6 +3379,9 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)

>>>>>   set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,

>>>>> 					   aarch64_execute_dwarf_cfa_vendor_op);

>>>>> 

>>>>> +  /* Permanent/Program breakpoint handling.  */

>>>>> +  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);

>>>>> +

>>>>>   /* Add some default predicates.  */

>>>>>   frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);

>>>>>   dwarf2_append_unwinders (gdbarch);

>>>>> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c

>>>>> index a1a003f91f..99c9f281be 100644

>>>>> --- a/gdb/arch-utils.c

>>>>> +++ b/gdb/arch-utils.c

>>>>> @@ -876,6 +876,13 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)

>>>>>   return 0;

>>>>> }

>>>> Add "/* See arch-utils.h.  */" ...

>>> 

>>> Fixed.

>>> 

>>>>> 

>>>>> +bool default_insn_is_breakpoint (struct gdbarch *gdbarch,

>>>>> +				 const gdb_byte  *insn,

>>>>> +				 unsigned int insn_size)

>>>>> +{

>>>>> +  return false;

>>>> I don’t like that this is just returning false, as it’s not really doing what the function name says.

>>>> How about if the function did this:

>>>>   return (memcmp (target_mem, bpoint, len) == 0);

>>>> Then remove the memcmp from program_breakpoint_here_p.

>>> 

>>> I agree it would be cleaner, but ...

>>> 

>>>> You’ll probably have to move the call to gdbarch_breakpoint_from_pc into here too.

>>> 

>>> ... this depends on calling gdbarch_breakpoint_from_pc to fetch bpoint, and gdbarch_breakpoint_from_pc requires the address information so it can determine the breakpoint kind.

>>> 

>>> Passing in the address is a bit out of scope for what the function is supposed to do (verify if a particular instruction is a breakpoint).

>>> 

>>> I don't have a strong objection towards passing in the address (or NULL if no address) if others are OK with it.

>> How about replacing program_breakpoint_here_p with

>> gdbarch_program_breakpoint_here_p(struct gdbarch *gdbarch, CORE_ADDR address) ?

>> default_program_breakpoint_here_p would be an exact copy of the existing program_breakpoint_here_p.

>> aarch64_program_breakpoint_here_p would do the copy to memory then the same as aarch64_insn_is_breakpoint.

> 

> It sounds interesting at first, but i'm not sure about it. We'll save a memory comparison but will duplicate the code to gdbarch_breakpoint_from_pc to every arch that sets its own gdbarch_program_breakpoint_here_p.

> 

> At least the old function dealt with just arch-specific bits, whereas the <arch>_program_breakpoint_here_p implementation will need to do a generic check + generic memory read as well, then do the arch-specific checks.

> 

> Thoughts?



It should be rare that any other architecture needs to define their own
gdbarch_program_breakpoint_here_p function.

However, let's rewind a little. My concern was that in the existing code, the common
program_breakpoint_here_p is assuming that the target has a single breakpoint instruction,
which it obtains by calling gdbarch_breakpoint_from_pc. On AArch64, we have multiple patterns
to match. With your patch, program_breakpoint_here_p now checks both the single pattern and
multiple pattern cases, which feels wrong. Instead the common code should just ask the target
code “does this address contain a breakpoint?”

I suggested creating gdbarch_program_breakpoint_here_p as that would reduce the number of
functions called, which helps when trying to follow the code logic.
However, I’m happy for the target_read_memory to remain in common code, then pass that down
to the arch specific versions.

I’m not sure if anything else uses it, but maybe the call to set_gdbarch_breakpoint_kind_from_pc
in aarch64-tdep.c should probably be removed too.


Alan.
Luis Machado Jan. 13, 2020, 12:50 p.m. UTC | #7
On 1/9/20 12:59 PM, Aktemur, Tankut Baris wrote:
> On Monday, December 23, 2019 6:35 PM, Luis Machado wrote:
>> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
>> index 1d5fb2001d..c69361d4ea 100644
>> --- a/gdb/aarch64-tdep.c
>> +++ b/gdb/aarch64-tdep.c
>> @@ -1201,6 +1201,28 @@ aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,
>>     return false;
>>   }
>>
>> +#define BRK_INSN_MASK 0xd4200000
> 
> I have a general question here.  Given that GDB is using C++11, would it
> make more sense to have this as
> 
>    static constexpr uint32_t BRK_INSN_MASK = 0xd4200000;
> 
> for more type-safety for the uses of this #define?
> 

I guess so. I have no problem with it, so i went ahead and fixed it and 
the other nits.

Thanks!
diff mbox

Patch

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index 1d5fb2001d..c69361d4ea 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -1201,6 +1201,28 @@  aarch64_execute_dwarf_cfa_vendor_op (struct gdbarch *gdbarch, gdb_byte op,
   return false;
 }
 
+#define BRK_INSN_MASK 0xd4200000
+
+/* Implementation of gdbarch_insn_is_breakpoint for aarch64.  */
+
+static bool
+aarch64_insn_is_breakpoint (gdbarch *gdbarch,
+			    const gdb_byte *insn,
+			    unsigned int insn_size)
+{
+  gdb_assert (insn != nullptr);
+
+  uint32_t i;
+
+  i = (uint32_t) extract_unsigned_integer (insn, insn_size,
+					   gdbarch_byte_order (gdbarch));
+
+  /* Check if INSN is a BRK instruction pattern.  There are multiple choices
+     of such instructions with different immediate values.  Different OS' may
+     use a different variation, but they have the same outcome.  */
+  return (i & BRK_INSN_MASK) == BRK_INSN_MASK;
+}
+
 /* When arguments must be pushed onto the stack, they go on in reverse
    order.  The code below implements a FILO (stack) to do this.  */
 
@@ -3357,6 +3379,9 @@  aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_execute_dwarf_cfa_vendor_op (gdbarch,
 					   aarch64_execute_dwarf_cfa_vendor_op);
 
+  /* Permanent/Program breakpoint handling.  */
+  set_gdbarch_insn_is_breakpoint (gdbarch, aarch64_insn_is_breakpoint);
+
   /* Add some default predicates.  */
   frame_unwind_append_unwinder (gdbarch, &aarch64_stub_unwind);
   dwarf2_append_unwinders (gdbarch);
diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index a1a003f91f..99c9f281be 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -876,6 +876,13 @@  int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)
   return 0;
 }
 
+bool default_insn_is_breakpoint (struct gdbarch *gdbarch,
+				 const gdb_byte  *insn,
+				 unsigned int insn_size)
+{
+  return false;
+}
+
 void
 default_skip_permanent_breakpoint (struct regcache *regcache)
 {
diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index 48ff3bb9a1..77ffe8190c 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -227,6 +227,9 @@  extern int default_return_in_first_hidden_param_p (struct gdbarch *,
 extern int default_insn_is_call (struct gdbarch *, CORE_ADDR);
 extern int default_insn_is_ret (struct gdbarch *, CORE_ADDR);
 extern int default_insn_is_jump (struct gdbarch *, CORE_ADDR);
+extern bool default_insn_is_breakpoint (struct gdbarch *gdbarch,
+					const gdb_byte *insn,
+					unsigned int insn_size);
 
 /* Do-nothing version of vsyscall_range.  Returns false.  */
 
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 904abda8db..ffb7f7f8be 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -8599,14 +8599,23 @@  program_breakpoint_here_p (struct gdbarch *gdbarch, CORE_ADDR address)
   target_mem = (gdb_byte *) alloca (len);
 
   /* Enable the automatic memory restoration from breakpoints while
-     we read the memory.  Otherwise we could say about our temporary
-     breakpoints they are permanent.  */
+     we read the memory.  Otherwise we may find temporary breakpoints, ones
+     inserted by GDB, and flag them as permanent breakpoints.  */
   scoped_restore restore_memory
     = make_scoped_restore_show_memory_breakpoints (0);
 
-  if (target_read_memory (address, target_mem, len) == 0
-      && memcmp (target_mem, bpoint, len) == 0)
-    return 1;
+  if (target_read_memory (address, target_mem, len) == 0)
+    {
+      /* Check if this is a breakpoint instruction for this architecture,
+	 including ones used by GDB. 
+
+	 Some architectures have more than one possible breakpoint
+	 instruction, but GDB does not use all of them.  We should detect those
+	 as well.  */
+      if (gdbarch_insn_is_breakpoint (gdbarch, target_mem, len)
+	  ||  memcmp (target_mem, bpoint, len) == 0)
+	return 1;
+    }
 
   return 0;
 }
diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index 59c97da985..9e21ba7eca 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -345,6 +345,7 @@  struct gdbarch
   gdbarch_insn_is_call_ftype *insn_is_call;
   gdbarch_insn_is_ret_ftype *insn_is_ret;
   gdbarch_insn_is_jump_ftype *insn_is_jump;
+  gdbarch_insn_is_breakpoint_ftype *insn_is_breakpoint;
   gdbarch_auxv_parse_ftype *auxv_parse;
   gdbarch_print_auxv_entry_ftype *print_auxv_entry;
   gdbarch_vsyscall_range_ftype *vsyscall_range;
@@ -464,6 +465,7 @@  gdbarch_alloc (const struct gdbarch_info *info,
   gdbarch->insn_is_call = default_insn_is_call;
   gdbarch->insn_is_ret = default_insn_is_ret;
   gdbarch->insn_is_jump = default_insn_is_jump;
+  gdbarch->insn_is_breakpoint = default_insn_is_breakpoint;
   gdbarch->print_auxv_entry = default_print_auxv_entry;
   gdbarch->vsyscall_range = default_vsyscall_range;
   gdbarch->infcall_mmap = default_infcall_mmap;
@@ -708,6 +710,7 @@  verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of insn_is_call, invalid_p == 0 */
   /* Skip verify of insn_is_ret, invalid_p == 0 */
   /* Skip verify of insn_is_jump, invalid_p == 0 */
+  /* Skip verify of insn_is_breakpoint, invalid_p == 0 */
   /* Skip verify of auxv_parse, has predicate.  */
   /* Skip verify of print_auxv_entry, invalid_p == 0 */
   /* Skip verify of vsyscall_range, invalid_p == 0 */
@@ -1137,6 +1140,9 @@  gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   fprintf_unfiltered (file,
                       "gdbarch_dump: inner_than = <%s>\n",
                       host_address_to_string (gdbarch->inner_than));
+  fprintf_unfiltered (file,
+                      "gdbarch_dump: insn_is_breakpoint = <%s>\n",
+                      host_address_to_string (gdbarch->insn_is_breakpoint));
   fprintf_unfiltered (file,
                       "gdbarch_dump: insn_is_call = <%s>\n",
                       host_address_to_string (gdbarch->insn_is_call));
@@ -4928,6 +4934,23 @@  set_gdbarch_insn_is_jump (struct gdbarch *gdbarch,
   gdbarch->insn_is_jump = insn_is_jump;
 }
 
+bool
+gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->insn_is_breakpoint != NULL);
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_insn_is_breakpoint called\n");
+  return gdbarch->insn_is_breakpoint (gdbarch, insn, insn_size);
+}
+
+void
+set_gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch,
+                                gdbarch_insn_is_breakpoint_ftype insn_is_breakpoint)
+{
+  gdbarch->insn_is_breakpoint = insn_is_breakpoint;
+}
+
 int
 gdbarch_auxv_parse_p (struct gdbarch *gdbarch)
 {
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 78e05ecdcb..d94950b8f2 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -1545,6 +1545,13 @@  typedef int (gdbarch_insn_is_jump_ftype) (struct gdbarch *gdbarch, CORE_ADDR add
 extern int gdbarch_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr);
 extern void set_gdbarch_insn_is_jump (struct gdbarch *gdbarch, gdbarch_insn_is_jump_ftype *insn_is_jump);
 
+/* Return true if INSN of size INSN_SIZE acts like a permanent breakpoint and
+   false otherwise. */
+
+typedef bool (gdbarch_insn_is_breakpoint_ftype) (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size);
+extern bool gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, const gdb_byte *insn, unsigned int insn_size);
+extern void set_gdbarch_insn_is_breakpoint (struct gdbarch *gdbarch, gdbarch_insn_is_breakpoint_ftype *insn_is_breakpoint);
+
 /* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
    Return 0 if *READPTR is already at the end of the buffer.
    Return -1 if there is insufficient buffer for a whole entry.
diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index 331eb39278..dbf31ee8ae 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -1152,6 +1152,10 @@  m;int;insn_is_ret;CORE_ADDR addr;addr;;default_insn_is_ret;;0
 # Return non-zero if the instruction at ADDR is a jump; zero otherwise.
 m;int;insn_is_jump;CORE_ADDR addr;addr;;default_insn_is_jump;;0
 
+# Return true if INSN of size INSN_SIZE acts like a permanent breakpoint and
+# false otherwise.
+m;bool;insn_is_breakpoint;const gdb_byte *insn, unsigned int insn_size;insn, insn_size;;default_insn_is_breakpoint;;0
+
 # Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
 # Return 0 if *READPTR is already at the end of the buffer.
 # Return -1 if there is insufficient buffer for a whole entry.