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

[Tom de Vries <tdevries@suse.de>]

On 11/2/21 5:26 PM, Simon Marchi wrote:
> 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.
> 

The only mention I found in gdb/MAINTAINERS related to powerpc is Kevin,
and he approved it.

> 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.

Ack, good suggestion, done and committed.

Thanks,
- Tom