database/postgres
database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-04-18 13:44:19 +03:00
Code

jit: Use -mno-outline-atomics for bitcode on ARM.

Browse Source 
If the executable's .o files were produced by a compiler (probably gcc)
not using -moutline-atomics, and the corresponding .bc files were
produced by clang using -moutline-atomics (probably by default), then
the generated bitcode functions would have the target attribute
"+outline-atomics", and could fail at runtime when inlined.  If the
target ISA at bitcode generation time was armv8-a (the most conservative
aarch64 target, no LSE), then LLVM IR atomic instructions would generate
calls to functions in libgcc.a or libclang_rt.*.a that switch between
LL/SC and faster LSE instructions depending on a runtime AT_HWCAP check.
Since the corresponding .o files didn't need those functions, they
wouldn't have been included in the executable, and resolution would
fail.

At least Debian and Ubuntu are known to ship gcc and clang compilers
that 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 in
bitcode 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 functions
using atomics that are inlined by JIT must be rare in the wild given how
long it took for a bug report to arrive.  The reported case could be
reduced to:

postgres=# set jit_inline_above_cost = 0;
SET
postgres=# set jit_above_cost = 0;
SET
postgres=# select pg_last_wal_receive_lsn();
WARNING:  failed to resolve name __aarch64_swp4_acq_rel
FATAL:  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
This commit is contained in:
Thomas Munro 2024-11-22 14:53:21 +13:00
parent c06e71d1ac
commit 78c09bd9f9
2 changed files with 112 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

105
configure vendored
View File

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

7
configure.ac
View File

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