glibc/sysdeps/powerpc/powerpc64/configure.ac
Adhemerval Zanella aac54dcd37 powerpc: Define USE_PPC64_NOTOC iff compiler supports it
The @notoc usage only yields an advantage on ISA 3.1+ machine (power10)
and for ld.bfd also when it sees pcrel relocations used on the code
(generated if compiler targets ISA 3.1+).  On bfd case ISA 3.1+
instruction on stubs are used iff linker also sees the new pc-relative
relocations (for instance R_PPC64_D34), otherwise it generates default
stubs (ppc64_elf_check_relocs:4700).

This patch also help on linkers that do not implement this optimization,
since building for older ISA (such as 3.0 / power9) will also trigger
power10 stubs generation in the assembly code uses the NOTOC imacro.

Checked on powerpc64le-linux-gnu.

Reviewed-by: Fangrui Song <maskray@google.com>
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
2021-11-22 14:49:11 -03:00

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GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
# Local configure fragment for sysdeps/powerpc/powerpc64.
AC_CACHE_CHECK(for support for overlapping .opd entries,
libc_cv_overlapping_opd, [dnl
libc_cv_overlapping_opd=no
echo 'void foo (void) {}' > conftest.c
if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -S conftest.c -o conftest.s 1>&AS_MESSAGE_LOG_FD); then
changequote(,)dnl
if grep '\.TOC\.@tocbase' conftest.s > /dev/null; then
if grep '\.TOC\.@tocbase[ ]*,[ ]*0' conftest.s > /dev/null; then
:
else
libc_cv_overlapping_opd=yes
fi
fi
changequote([,])dnl
fi
rm -f conftest.c conftest.s
])
if test x$libc_cv_overlapping_opd = xyes; then
AC_DEFINE(USE_PPC64_OVERLAPPING_OPD)
fi
# We check if compiler supports @notoc generation since there is no
# gain by enabling it if it will be optimized away by the linker.
# It also helps linkers that might not optimize it and end up
# generating stubs with ISA 3.1 instruction even targetting older ISA.
AC_CACHE_CHECK([if the compiler supports @notoc],
libc_cv_ppc64_notoc, [dnl
cat > conftest.c <<EOF
int bar (void);
int foo (void) { return bar () + 1; }
EOF
libc_cv_ppc64_notoc=no
if AC_TRY_COMMAND([${CC-cc} $libc_cv_cc_submachine $CFLAGS $CPPFLAGS -S -o conftest.s conftest.c]) \
&& AC_TRY_COMMAND([grep -q -E 'bar@notoc' conftest.s])
then
libc_cv_ppc64_notoc=yes
fi
rm -rf conftest.*])
AS_IF([test x$libc_cv_ppc64_notoc = xyes],
[AC_DEFINE(USE_PPC64_NOTOC)])