Re: [PATCH v5 1/1] gdb: avoid conversion of SIGSEGV to SIGTRAP on user breakpoints

[Simon Marchi <simark@simark.ca>]

On 2026-09-02 15:20, Tom Tromey wrote:
>>>>>> Klaus Gerlicher <klaus.gerlicher@intel.com> writes:
> 
>> From: "Gerlicher, Klaus" <klaus.gerlicher@intel.com>
>> GDB converts signals GDB_SIGNAL_ILL, GDB_SIGNAL_SEGV and GDB_SIGNAL_EMT to
>> GDB_SIGNAL_TRAP if a breakpoint is inserted at the fault location.  This
>> conversion logic assumes that when these signals occur at a breakpoint
>> location, the signal was actually caused by hitting the breakpoint rather
>> than a genuine fault.
> 
> Thanks for the patch.
> 
>> Add a new gdbarch function, imprecise_pagefault_reporting, that allows the
>> signal conversion from GDB_SIGNAL_SEGV to GDB_SIGNAL_TRAP to be skipped for
>> an architecture.  The default is false (conversion enabled), preserving
>> existing behavior.  Architectures with imprecise fault reporting should
>> override this to return true.
> 
> My first thought was that, without an implementation in the tree, this
> will cause gdb/check-gdbarch.py to complain.  However, I saw that the
> plan is a follow-up patch to use this.
> 
> Maybe temporarily marking this 'unused' would be good, provided that is
> removed in the follow-up.
> 
> Also I was wondering, why a Function and not a Value?
> 
>> +    predefault="[] () -> bool {return false;}",
> 
> This doesn't take arguments, so presumably just a value would be
> sufficient?

Yeah if it can be a value, let's make it a value.

My only comment would be that here:

  if (ecs->ws.kind () == TARGET_WAITKIND_STOPPED
      && (ecs->ws.sig () == GDB_SIGNAL_ILL
	  || (ecs->ws.sig () == GDB_SIGNAL_SEGV
	      && !gdbarch_imprecise_pagefault_reporting
		  (target_thread_architecture (ecs->event_thread->ptid)))
	  || ecs->ws.sig () == GDB_SIGNAL_EMT))

You would need some extra parentheses to make emacs happy:

  if (ecs->ws.kind () == TARGET_WAITKIND_STOPPED
      && (ecs->ws.sig () == GDB_SIGNAL_ILL
	  || (ecs->ws.sig () == GDB_SIGNAL_SEGV
	      && !(gdbarch_imprecise_pagefault_reporting
		   (target_thread_architecture (ecs->event_thread->ptid))))
	  || ecs->ws.sig () == GDB_SIGNAL_EMT))

With that and Tom's two suggestions (make it a value and temporarily
mark unused), the patch LGTM.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon