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