On Thu, Jul 3, 2025 at 12:01 PM H.J. Lu <hjl.to...@gmail.com> wrote: > > When profiling is enabled with shrink wrapping, the mcount call may not > be placed at the function entry after > > pushq %rbp > movq %rsp,%rbp > > As the result, the profile data may be skewed which makes PGO less > effective. > > Add --enable-x86-64-mfentry to enable -mfentry by default to use > __fentry__, added to glibc in 2010 by: > > commit d22e4cc9397ed41534c9422d0b0ffef8c77bfa53 > Author: Andi Kleen <a...@linux.intel.com> > Date: Sat Aug 7 21:24:05 2010 -0700 > > x86: Add support for frame pointer less mcount > > instead of mcount, which is placed before the prologue so that -pg can > be used with -fshrink-wrap-separate enabled at -O1. This option is > 64-bit only because __fentry__ doesn't support PIC in 32-bit mode. > > Also warn -pg without -mfentry with shrink wrapping enabled. The warning > is disable for PIC in 32-bit mode. > > gcc/ > > PR target/120881 > * config.in: Regenerated. > * configure: Likewise. > * configure.ac: Add --enable-x86-64-mfentry. > * config/i386/i386-options.cc (ix86_option_override_internal): > Enable __fentry__ in 64-bit mode if ENABLE_X86_64_MFENTRY is set > to 1. Warn -pg without -mfentry with shrink wrapping enabled. > * doc/install.texi: Document --enable-x86-64-mfentry. > > gcc/testsuite/ > > PR target/120881 > * gcc.target/i386/pr120881-1a.c: New test. > * gcc.target/i386/pr120881-1b.c: Likewise. > * gcc.target/i386/pr120881-1c.c: Likewise. > * gcc.target/i386/pr120881-1d.c: Likewise. > * gcc.target/i386/pr120881-2a.c: Likewise. > * gcc.target/i386/pr120881-2b.c: Likewise. > * lib/target-supports.exp (check_effective_target_fentry): New. > > OK for master?
OK in principle, but please allow some time for distro maintainers (CC'd) to voice their opinion. Thanks, Uros.
