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powerpc: Define USE_PPC64_NOTOC iff compiler supports it

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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>
This commit is contained in:
Adhemerval Zanella 2021-11-06 09:38:09 -03:00
parent bc801b3a40
commit aac54dcd37
2 changed files with 43 additions and 24 deletions
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42
sysdeps/powerpc/powerpc64/configure vendored
View File

@ -32,26 +32,36 @@ if test x$libc_cv_overlapping_opd = xyes; then
fi
# @notoc started to be supported in GNU Binutils 2.31.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the assembler supports @notoc" >&5
$as_echo_n "checking if the assembler supports @notoc... " >&6; }
# 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.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the compiler supports @notoc" >&5
$as_echo_n "checking if the compiler supports @notoc... " >&6; }
if ${libc_cv_ppc64_notoc+:} false; then :
$as_echo_n "(cached) " >&6
else
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
void foo (void) {asm("b foo@notoc");}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
libc_cv_ppc64_notoc=yes
else
cat > conftest.c <<EOF
int bar (void);
int foo (void) { return bar () + 1; }
EOF
libc_cv_ppc64_notoc=no
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
if { ac_try='${CC-cc} $libc_cv_cc_submachine $CFLAGS $CPPFLAGS -S -o conftest.s conftest.c'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; } \
&& { ac_try='grep -q -E 'bar@notoc' conftest.s'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
then
libc_cv_ppc64_notoc=yes
fi
rm -rf conftest.*
fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ppc64_notoc" >&5
$as_echo "$libc_cv_ppc64_notoc" >&6; }

25
sysdeps/powerpc/powerpc64/configure.ac
View File

@ -22,13 +22,22 @@ if test x$libc_cv_overlapping_opd = xyes; then
AC_DEFINE(USE_PPC64_OVERLAPPING_OPD)
fi
# @notoc started to be supported in GNU Binutils 2.31.
AC_CACHE_CHECK([if the assembler supports @notoc],
libc_cv_ppc64_notoc, [
AC_COMPILE_IFELSE([AC_LANG_SOURCE([
void foo (void) {asm("b foo@notoc");}
])],
[libc_cv_ppc64_notoc=yes],
[libc_cv_ppc64_notoc=no])])
# We check if compiler supports @notoc generation since there is no
# gain by enabling it if it will be optimized away by the linker.
# It also helps linkers that might not optimize it and end up
# generating stubs with ISA 3.1 instruction even targetting older ISA.
AC_CACHE_CHECK([if the compiler supports @notoc],
libc_cv_ppc64_notoc, [dnl
cat > conftest.c <<EOF
int bar (void);
int foo (void) { return bar () + 1; }
EOF
libc_cv_ppc64_notoc=no
if AC_TRY_COMMAND([${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)])