Re: [PATCH][gdb/tdep, rs6000] Don't skip system call in skip_prologue

[Simon Marchi <simark@simark.ca>]

On 2021-11-02 7:33 a.m., Tom de Vries via Gdb-patches wrote:
> Hi,
> 
> I ran into a case where a breakpoint on _exit never triggered, because it was
> set past the end of the _exit prologue, past the end of the exit_group system
> call (which does not return).
> 
> Fix this by treating system calls the same as branches in skip_prologue:
> by default, don't skip.
> 
> Tested on ppc64le-linux, on a power 8 machine.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28527
> 
> Any comments?
> 
> Thanks,
> - Tom
> 
> [gdb/tdep, rs6000] Don't skip system call in skip_prologue
> 
> ---
>  gdb/rs6000-tdep.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index 78b4fd1a913..4830ed22593 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -2137,6 +2137,12 @@ skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc, CORE_ADDR lim_pc,
>  	    /* Never skip branches.  */
>  	    break;
>  
> +	  /* Test based on opcode and mask values of
> +	     powerpc_opcodes[svc..svcla] in opcodes/ppc-opc.c.  */
> +	  if ((op & 0xffff0000) == 0x44000000)
> +	    /* Never skip system calls.  */
> +	    break;
> +
>  	  if (num_skip_non_prologue_insns++ > max_skip_non_prologue_insns)
>  	    /* Do not scan too many insns, scanning insns is expensive with
>  	       remote targets.  */
> 


The explanation makes sense, but I think a powerpc maintainer should ack the
patch.

And I think it would be useful to paste the "disassembly /r" of the _exit
function in the commit message, showing where the breakpoint used to be
placed, and where it is placed now.

Simon