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__()
---
gcc/config/i386/i386.cc | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index be5e27fc391..6be6ddcbb3c 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -23154,6 +23154,8 @@ x86_print_call_or_nop (FILE *file, const char *target)
if (flag_nop_mcount || !strcmp (target, "nop"))
/* 5 byte nop: nopl 0(%[re]ax,%[re]ax,1) */
fprintf (file, "1:" ASM_BYTE "0x0f, 0x1f, 0x44, 0x00, 0x00\n");
+ else if (!TARGET_PECOFF && flag_pic && flag_plt)
+ fprintf (file, "1:\tcall\t%s@PLT\n", target);
else
fprintf (file, "1:\tcall\t%s\n", target);
}
@@ -23317,7 +23319,7 @@ x86_function_profiler (FILE *file, int labelno
ATTRIBUTE_UNUSED)
break;
case CM_SMALL_PIC:
case CM_MEDIUM_PIC:
- if (!ix86_direct_extern_access)
+ if (!flag_plt)
{
if (ASSEMBLER_DIALECT == ASM_INTEL)
fprintf (file, "1:\tcall\t[QWORD PTR %s@GOTPCREL[rip]]\n",
--
2.49.0.504.g3bcea36a83-goog
