[5/8] Step over fork/vfork syscall insn in gdbserver

  We can also extend disp-step-syscall.exp to test GDBserver step over
breakpoint on syscall instruction.  That is, we set a breakpoint
with a false condition on syscall instruction, so that GDBserver will
step over it.

This test triggers a GDBserver internal error, which can be fixed by
this series.

(gdb) PASS: gdb.base/disp-step-syscall.exp: fork: break cond on target: break on syscall insns
continue^M
Continuing.^M
Remote connection closed^M
(gdb) FAIL: gdb.base/disp-step-syscall.exp: fork: break cond on target: continue to fork again

In GDBserver, there is an internal error,

/home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been detected.
unsuspend LWP 25554, suspended=-1

the simplified reproducer is like,

$ ./gdb ./testsuite/outputs/gdb.base/disp-step-syscall/disp-step-fork
(gdb) b main
(gdb) c
(gdb) disassemble fork // in order to find the address of insn 'syscall'
....
   0x00007ffff7ad6023 <+179>:	syscall
(gdb) b *0x00007ffff7ad6023 if main == 0
(gdb) c

gdb/testsuite:

2016-02-19  Yao Qi  <yao.qi@linaro.org>

	* gdb.base/disp-step-fork.c (main): Increase loop boundary.
	* gdb.base/disp-step-vfork.c (main): Likewise.
	* gdb.base/disp-step-syscall.exp (disp_step_cross_syscall): Test
	breakpoint condition evaluated on the target side.
---
 gdb/testsuite/gdb.base/disp-step-fork.c      |  2 +-
 gdb/testsuite/gdb.base/disp-step-syscall.exp | 38 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/disp-step-vfork.c     |  2 +-
 3 files changed, 40 insertions(+), 2 deletions(-)
  

Just one comment nit.

On 02/19/2016 12:36 PM, Yao Qi wrote:
> We can also extend disp-step-syscall.exp to test GDBserver step over
> breakpoint on syscall instruction.  That is, we set a breakpoint
> with a false condition on syscall instruction, so that GDBserver will
> step over it.
>
> This test triggers a GDBserver internal error, which can be fixed by
> this series.
>
> (gdb) PASS: gdb.base/disp-step-syscall.exp: fork: break cond on target: break on syscall insns
> continue^M
> Continuing.^M
> Remote connection closed^M
> (gdb) FAIL: gdb.base/disp-step-syscall.exp: fork: break cond on target: continue to fork again
>
> In GDBserver, there is an internal error,
>
> /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been detected.
> unsuspend LWP 25554, suspended=-1
>
> the simplified reproducer is like,
>
> $ ./gdb ./testsuite/outputs/gdb.base/disp-step-syscall/disp-step-fork
> (gdb) b main
> (gdb) c
> (gdb) disassemble fork // in order to find the address of insn 'syscall'
> ....
>     0x00007ffff7ad6023 <+179>:	syscall
> (gdb) b *0x00007ffff7ad6023 if main == 0
> (gdb) c
>
> gdb/testsuite:
>
> 2016-02-19  Yao Qi  <yao.qi@linaro.org>
>
> 	* gdb.base/disp-step-fork.c (main): Increase loop boundary.
> 	* gdb.base/disp-step-vfork.c (main): Likewise.
> 	* gdb.base/disp-step-syscall.exp (disp_step_cross_syscall): Test
> 	breakpoint condition evaluated on the target side.
> ---
>   gdb/testsuite/gdb.base/disp-step-fork.c      |  2 +-
>   gdb/testsuite/gdb.base/disp-step-syscall.exp | 38 ++++++++++++++++++++++++++++
>   gdb/testsuite/gdb.base/disp-step-vfork.c     |  2 +-
>   3 files changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.base/disp-step-fork.c b/gdb/testsuite/gdb.base/disp-step-fork.c
> index d8d602f..6d477ea 100644
> --- a/gdb/testsuite/gdb.base/disp-step-fork.c
> +++ b/gdb/testsuite/gdb.base/disp-step-fork.c
> @@ -26,7 +26,7 @@ main (void)
>   {
>     int i, pid;
>
> -  for (i = 0; i < 4; i++)
> +  for (i = 0; i < 6; i++)
>       {
>         pid = fork ();
>         if (pid == 0) /* child */
> diff --git a/gdb/testsuite/gdb.base/disp-step-syscall.exp b/gdb/testsuite/gdb.base/disp-step-syscall.exp
> index 9e43fbb..53ac1e1 100644
> --- a/gdb/testsuite/gdb.base/disp-step-syscall.exp
> +++ b/gdb/testsuite/gdb.base/disp-step-syscall.exp
> @@ -153,6 +153,44 @@ proc disp_step_cross_syscall { syscall } {
>       }
>   	}
>
> +	with_test_prefix "break cond on target" {
> +	    set cond_bp_target 1
> +
> +	    set test "set breakpoint condition-evaluation target"
> +	    gdb_test_multiple $test $test {
> +		-re "warning: Target does not support breakpoint condition evaluation.\r\nUsing host evaluation mode instead.\r\n$gdb_prompt $" {
> +		    # Target doesn't support breakpoint condition
> +		    # evaluation on its side.
> +		    set cond_bp_target 0
> +		}
> +		-re "^$test\r\n$gdb_prompt $" {
> +		}
> +	    }
> +
> +	    if { $cond_bp_target } {
> +		gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
> +		    "continue to $syscall"
> +
> +		# Create a breakpoint with the condition which is false.
> +		set syscall_insn_bp 0
> +		gdb_test_multiple "break \*$syscall_insn_addr if main == 0" \
> +		    "break on syscall insns" {
> +			-re "Breakpoint (\[0-9\]*) at .*$gdb_prompt $" {
> +			    set syscall_insn_bp $expect_out(1,string)
> +			    pass "break on syscall insns"
> +			}
> +		    }
> +
> +		gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
> +		    "continue to $syscall again"
> +
> +		# Delete breakpoint syscall insns to avoid interference to

"... interference with..."?
  

LGTM.

On 02/19/2016 02:36 PM, Yao Qi wrote:

> +		# Create a breakpoint with the condition which is false.

Suggest:

   # Create a breakpoint with a condition that evals false.

Thanks,
Pedro Alves