[v3] Fix inferior memory reading in GDBServer for arm/aarch32
Commit Message
In this v3:
* Stack reads are now done with ->read_memory
* Note tha this invalidated PATH 3/3 about sparc, since it's also a read from stack..
Before this patch, some functions would read the inferior memory with
(*the_target)->read_memory, which returns the raw memory, rather than the
shadowed memory.
This is wrong since these functions do not expect to read a breakpoint
instruction and can lead to invalid behavior.
Use of raw memory in get_next_pcs_read_memory_unsigned_integer for example
could lead to get_next_pc returning an invalid pc.
Here's how this would happen:
In non-stop:
the user issues:
thread 1
step&
thread 2
step&
thread 3
step&
In a similar way as non-stop-fair-events.exp (threads are looping).
GDBServer:
linux_resume is called
GDBServer has pending events,
threads are not resumed and single-step breakpoint for thread 1 not installed.
linux_wait_1 is called with a pending event on thread 2 at pc A
GDBServer handles the event and calls proceed_all_lwps
This calls proceed_one_lwp and installs single-step breakpoints on all
the threads that need one.
Now since thread 1 needs to install a single-step breakpoint and is at pc B
(different than thread 2), a step-over is not initiated and get_next_pc
is called to figure out the next instruction from pc B.
However it may just be that thread 3 as a single step breakpoint at pc
B. And thus get_next_pc fails.
This situation is tested with non-stop-fair-events.exp.
In other words, single-step breakpoints are installed in proceed_one_lwp
for each thread. GDBserver proceeds two threads for resume_step, as
requested by GDB, and the thread proceeded later may see the single-step
breakpoints installed for the thread proceeded just now.
Tested on gdbserver-native/-m{thumb,arm} no regressions.
gdb/gdbserver/ChangeLog:
* linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
target_read_memory.
* linux-arm-low.c (get_next_pcs_read_memory_unsigned_integer): Likewise.
(get_next_pcs_syscall_next_pc): Likewise.
---
gdb/gdbserver/linux-aarch32-low.c | 4 ++--
gdb/gdbserver/linux-arm-low.c | 5 +++--
2 files changed, 5 insertions(+), 4 deletions(-)
Comments
Ping. (Sorry I had a mistake in Yao's email on 1st post)
Antoine Tremblay writes:
> In this v3:
> * Stack reads are now done with ->read_memory
> * Note tha this invalidated PATH 3/3 about sparc, since it's also a read from stack..
>
> Before this patch, some functions would read the inferior memory with
> (*the_target)->read_memory, which returns the raw memory, rather than the
> shadowed memory.
>
> This is wrong since these functions do not expect to read a breakpoint
> instruction and can lead to invalid behavior.
>
> Use of raw memory in get_next_pcs_read_memory_unsigned_integer for example
> could lead to get_next_pc returning an invalid pc.
>
> Here's how this would happen:
>
> In non-stop:
>
> the user issues:
>
> thread 1
> step&
> thread 2
> step&
> thread 3
> step&
>
> In a similar way as non-stop-fair-events.exp (threads are looping).
>
> GDBServer:
>
> linux_resume is called
> GDBServer has pending events,
> threads are not resumed and single-step breakpoint for thread 1 not installed.
>
> linux_wait_1 is called with a pending event on thread 2 at pc A
> GDBServer handles the event and calls proceed_all_lwps
> This calls proceed_one_lwp and installs single-step breakpoints on all
> the threads that need one.
>
> Now since thread 1 needs to install a single-step breakpoint and is at pc B
> (different than thread 2), a step-over is not initiated and get_next_pc
> is called to figure out the next instruction from pc B.
>
> However it may just be that thread 3 as a single step breakpoint at pc
> B. And thus get_next_pc fails.
>
> This situation is tested with non-stop-fair-events.exp.
>
> In other words, single-step breakpoints are installed in proceed_one_lwp
> for each thread. GDBserver proceeds two threads for resume_step, as
> requested by GDB, and the thread proceeded later may see the single-step
> breakpoints installed for the thread proceeded just now.
>
> Tested on gdbserver-native/-m{thumb,arm} no regressions.
>
> gdb/gdbserver/ChangeLog:
>
> * linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
> target_read_memory.
> * linux-arm-low.c (get_next_pcs_read_memory_unsigned_integer): Likewise.
> (get_next_pcs_syscall_next_pc): Likewise.
> ---
> gdb/gdbserver/linux-aarch32-low.c | 4 ++--
> gdb/gdbserver/linux-arm-low.c | 5 +++--
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/gdbserver/linux-aarch32-low.c b/gdb/gdbserver/linux-aarch32-low.c
> index 5547cf6491..4ff34b626b 100644
> --- a/gdb/gdbserver/linux-aarch32-low.c
> +++ b/gdb/gdbserver/linux-aarch32-low.c
> @@ -237,11 +237,11 @@ arm_breakpoint_kind_from_pc (CORE_ADDR *pcptr)
> *pcptr = UNMAKE_THUMB_ADDR (*pcptr);
>
> /* Check whether we are replacing a thumb2 32-bit instruction. */
> - if ((*the_target->read_memory) (*pcptr, buf, 2) == 0)
> + if (target_read_memory (*pcptr, buf, 2) == 0)
> {
> unsigned short inst1 = 0;
>
> - (*the_target->read_memory) (*pcptr, (gdb_byte *) &inst1, 2);
> + target_read_memory (*pcptr, (gdb_byte *) &inst1, 2);
> if (thumb_insn_size (inst1) == 4)
> return ARM_BP_KIND_THUMB2;
> }
> diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
> index ed9b3562a8..930cc34f71 100644
> --- a/gdb/gdbserver/linux-arm-low.c
> +++ b/gdb/gdbserver/linux-arm-low.c
> @@ -263,7 +263,8 @@ get_next_pcs_read_memory_unsigned_integer (CORE_ADDR memaddr,
> ULONGEST res;
>
> res = 0;
> - (*the_target->read_memory) (memaddr, (unsigned char *) &res, len);
> + target_read_memory (memaddr, (unsigned char *) &res, len);
> +
> return res;
> }
>
> @@ -804,7 +805,7 @@ get_next_pcs_syscall_next_pc (struct arm_get_next_pcs *self)
> unsigned long this_instr;
> unsigned long svc_operand;
>
> - (*the_target->read_memory) (pc, (unsigned char *) &this_instr, 4);
> + target_read_memory (pc, (unsigned char *) &this_instr, 4);
> svc_operand = (0x00ffffff & this_instr);
>
> if (svc_operand) /* OABI. */
On 16-12-09 07:46:25, Antoine Tremblay wrote:
>
> This situation is tested with non-stop-fair-events.exp.
>
> In other words, single-step breakpoints are installed in proceed_one_lwp
> for each thread. GDBserver proceeds two threads for resume_step, as
> requested by GDB, and the thread proceeded later may see the single-step
> breakpoints installed for the thread proceeded just now.
>
> Tested on gdbserver-native/-m{thumb,arm} no regressions.
I assume this patch fixes fails in non-stop-fair-events.exp.
>
> gdb/gdbserver/ChangeLog:
>
> * linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
> target_read_memory.
> * linux-arm-low.c (get_next_pcs_read_memory_unsigned_integer): Likewise.
> (get_next_pcs_syscall_next_pc): Likewise.
Patch is good to me.
Yao Qi writes:
> On 16-12-09 07:46:25, Antoine Tremblay wrote:
>>
>> This situation is tested with non-stop-fair-events.exp.
>>
>> In other words, single-step breakpoints are installed in proceed_one_lwp
>> for each thread. GDBserver proceeds two threads for resume_step, as
>> requested by GDB, and the thread proceeded later may see the single-step
>> breakpoints installed for the thread proceeded just now.
>>
>> Tested on gdbserver-native/-m{thumb,arm} no regressions.
>
> I assume this patch fixes fails in non-stop-fair-events.exp.
No, it helps but fails are still present, to fix things you need
https://sourceware.org/ml/gdb-patches/2016-11/msg00939.html
and
https://sourceware.org/ml/gdb-patches/2016-11/msg00940.html
If you can take a look at those too it would be nice ?
>
>>
>> gdb/gdbserver/ChangeLog:
>>
>> * linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
>> target_read_memory.
>> * linux-arm-low.c (get_next_pcs_read_memory_unsigned_integer): Likewise.
>> (get_next_pcs_syscall_next_pc): Likewise.
>
> Patch is good to me.
Patch is pushed in.
@@ -237,11 +237,11 @@ arm_breakpoint_kind_from_pc (CORE_ADDR *pcptr)
*pcptr = UNMAKE_THUMB_ADDR (*pcptr);
/* Check whether we are replacing a thumb2 32-bit instruction. */
- if ((*the_target->read_memory) (*pcptr, buf, 2) == 0)
+ if (target_read_memory (*pcptr, buf, 2) == 0)
{
unsigned short inst1 = 0;
- (*the_target->read_memory) (*pcptr, (gdb_byte *) &inst1, 2);
+ target_read_memory (*pcptr, (gdb_byte *) &inst1, 2);
if (thumb_insn_size (inst1) == 4)
return ARM_BP_KIND_THUMB2;
}
@@ -263,7 +263,8 @@ get_next_pcs_read_memory_unsigned_integer (CORE_ADDR memaddr,
ULONGEST res;
res = 0;
- (*the_target->read_memory) (memaddr, (unsigned char *) &res, len);
+ target_read_memory (memaddr, (unsigned char *) &res, len);
+
return res;
}
@@ -804,7 +805,7 @@ get_next_pcs_syscall_next_pc (struct arm_get_next_pcs *self)
unsigned long this_instr;
unsigned long svc_operand;
- (*the_target->read_memory) (pc, (unsigned char *) &this_instr, 4);
+ target_read_memory (pc, (unsigned char *) &this_instr, 4);
svc_operand = (0x00ffffff & this_instr);
if (svc_operand) /* OABI. */