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Commit78c09bd

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jit: Use -mno-outline-atomics for bitcode on ARM.
If the executable's .o files were produced by a compiler (probably gcc)not using -moutline-atomics, and the corresponding .bc files wereproduced by clang using -moutline-atomics (probably by default), thenthe generated bitcode functions would have the target attribute"+outline-atomics", and could fail at runtime when inlined. If thetarget ISA at bitcode generation time was armv8-a (the most conservativeaarch64 target, no LSE), then LLVM IR atomic instructions would generatecalls to functions in libgcc.a or libclang_rt.*.a that switch betweenLL/SC and faster LSE instructions depending on a runtime AT_HWCAP check.Since the corresponding .o files didn't need those functions, theywouldn't have been included in the executable, and resolution wouldfail.At least Debian and Ubuntu are known to ship gcc and clang compilersthat target armv8-a but differ on the use of outline atomics by default.Fix, by suppressing the outline atomics attribute in bitcode explicitly.Inline LL/SC instructions will be generated for atomic operations inbitcode built for armv8-a. Only configure scripts are adjusted for now,because the meson build system doesn't generate bitcode yet.This doesn't seem to be a new phenomenon, so real cases of functionsusing atomics that are inlined by JIT must be rare in the wild given howlong it took for a bug report to arrive. The reported case could bereduced to:postgres=# set jit_inline_above_cost = 0;SETpostgres=# set jit_above_cost = 0;SETpostgres=# select pg_last_wal_receive_lsn();WARNING: failed to resolve name __aarch64_swp4_acq_relFATAL: fatal llvm error: Program used external function'__aarch64_swp4_acq_rel' which could not be resolved!The change doesn't affect non-ARM systems or later target ISAs.Back-patch to all supported releases.Reported-by: Alexander Kozhemyakin <a.kozhemyakin@postgrespro.ru>Discussion:https://postgr.es/m/18610-37bf303f904fede3%40postgresql.org
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2 files changed

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‎configure

Lines changed: 105 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7283,6 +7283,111 @@ if test x"$pgac_cv_prog_CLANGXX_cxxflags__fexcess_precision_standard" = x"yes";
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fi
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# Ideally bitcode should perhaps match $CC's use, or not, of outline atomic
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# functions, but for now we err on the side of suppressing them in bitcode,
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# because we can't assume they're available at runtime. This affects aarch64
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# builds using the basic armv8-a ISA without LSE support.
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -mno-outline-atomics, for BITCODE_CFLAGS" >&5
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$as_echo_n "checking whether ${CLANG} supports -mno-outline-atomics, for BITCODE_CFLAGS... " >&6; }
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if ${pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics+:} false; then :
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$as_echo_n "(cached) " >&6
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else
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pgac_save_CXXFLAGS=$CXXFLAGS
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pgac_save_CXX=$CXX
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CXX=${CLANG}
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CXXFLAGS="${BITCODE_CFLAGS} -mno-outline-atomics"
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ac_save_cxx_werror_flag=$ac_cxx_werror_flag
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ac_cxx_werror_flag=yes
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ac_ext=cpp
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ac_cpp='$CXXCPP $CPPFLAGS'
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ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
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ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
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ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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int
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main ()
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{
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;
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return 0;
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}
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_ACEOF
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if ac_fn_cxx_try_compile "$LINENO"; then :
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pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics=yes
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else
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pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics=no
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fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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ac_ext=c
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ac_cpp='$CPP $CPPFLAGS'
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ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
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ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
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ac_compiler_gnu=$ac_cv_c_compiler_gnu
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ac_cxx_werror_flag=$ac_save_cxx_werror_flag
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CXXFLAGS="$pgac_save_CXXFLAGS"
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CXX="$pgac_save_CXX"
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" >&5
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$as_echo "$pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" >&6; }
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if test x"$pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" = x"yes"; then
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BITCODE_CFLAGS="${BITCODE_CFLAGS} -mno-outline-atomics"
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -mno-outline-atomics, for BITCODE_CXXFLAGS" >&5
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$as_echo_n "checking whether ${CLANG} supports -mno-outline-atomics, for BITCODE_CXXFLAGS... " >&6; }
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if ${pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics+:} false; then :
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$as_echo_n "(cached) " >&6
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else
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pgac_save_CXXFLAGS=$CXXFLAGS
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pgac_save_CXX=$CXX
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CXX=${CLANG}
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CXXFLAGS="${BITCODE_CXXFLAGS} -mno-outline-atomics"
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ac_save_cxx_werror_flag=$ac_cxx_werror_flag
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ac_cxx_werror_flag=yes
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ac_ext=cpp
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ac_cpp='$CXXCPP $CPPFLAGS'
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ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
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ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
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ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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int
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main ()
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{
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;
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return 0;
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}
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_ACEOF
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if ac_fn_cxx_try_compile "$LINENO"; then :
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pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics=yes
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else
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pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics=no
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fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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ac_ext=c
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ac_cpp='$CPP $CPPFLAGS'
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ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
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ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
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ac_compiler_gnu=$ac_cv_c_compiler_gnu
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ac_cxx_werror_flag=$ac_save_cxx_werror_flag
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CXXFLAGS="$pgac_save_CXXFLAGS"
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CXX="$pgac_save_CXX"
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" >&5
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$as_echo "$pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" >&6; }
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if test x"$pgac_cv_prog_CLANG_cxxflags__mno_outline_atomics" = x"yes"; then
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BITCODE_CXXFLAGS="${BITCODE_CXXFLAGS} -mno-outline-atomics"
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fi
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NOT_THE_CFLAGS=""
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS" >&5
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$as_echo_n "checking whether ${CLANG} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS... " >&6; }

‎configure.ac

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -633,6 +633,13 @@ if test "$with_llvm" = yes ; then
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PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, BITCODE_CFLAGS,[-fexcess-precision=standard])
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PGAC_PROG_VARCXX_VARFLAGS_OPT(CLANGXX, BITCODE_CXXFLAGS,[-fexcess-precision=standard])
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# Ideally bitcode should perhaps match $CC's use, or not, of outline atomic
637+
# functions, but for now we err on the side of suppressing them in bitcode,
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# because we can't assume they're available at runtime. This affects aarch64
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# builds using the basic armv8-a ISA without LSE support.
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PGAC_PROG_VARCXX_VARFLAGS_OPT(CLANG, BITCODE_CFLAGS,[-mno-outline-atomics])
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PGAC_PROG_VARCXX_VARFLAGS_OPT(CLANG, BITCODE_CXXFLAGS,[-mno-outline-atomics])
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NOT_THE_CFLAGS=""
637644
PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, NOT_THE_CFLAGS,[-Wunused-command-line-argument])
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if test -n "$NOT_THE_CFLAGS"; then

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