On Fri, Apr 4, 2025 at 9:00 AM Ard Biesheuvel <ardb+...@google.com> wrote:
>
> From: Ard Biesheuvel <a...@kernel.org>
>
> Commit bde21de1205 ("i386: Honour -mdirect-extern-access when calling
> __fentry__") updated the logic that emits mcount() / __fentry__() calls
> into function prologues when profiling is enabled, to avoid GOT-based
> indirect calls when a direct call would suffice.
>
> There are two problems with that change:
> - it relies on -mdirect-extern-access rather than -fno-plt to decide
> whether or not a direct [PLT based] call is appropriate;
> - for the PLT case, it falls through to x86_print_call_or_nop(), which
> does not emit the @PLT suffix, resulting in the wrong relocation to be
> used (R_X86_64_PC32 instead of R_X86_64_PLT32)
>
> Fix this by testing flag_plt instead of ix86_direct_extern_access, and
> updating x86_print_call_or_nop() to take flag_pic and flag_plt into
> account. This ensures that -mnop-mcount works as expected when emitting
> the PLT based profiling calls.
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119386
>
> Signed-off-by: Ard Biesheuvel <a...@kernel.org>
>
> gcc/ChangeLog:
>
> * config/i386/i386.cc (x86_function_profiler): Take
> ix86_direct_extern_access into account when generating calls
> to __fentry__()
I'm not a specialist in this part of the compiler, but all relevant
people took part in the (long) discussion in the PR and came to the
above consensus.
So, I'm rubber-stamping this patch OK.
Ard, are you able to commit the patch yourself, or I should commit it for you?
Thanks,
Uros.
