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Error out for clang on x86-32 without SSE2 support, no -fexcess-precision. 

As clang currently doesn't support -fexcess-precision=standard,
compiling x86-32 code with SSE2 disabled, can lead to problems with
floating point overflow checks and the like.

This issue was noticed because clang, on at least some BSDs, defaults
to i386 compatibility, whereas it defaults to pentium4 on Linux.  Our
forced usage of __builtin_isinf() lead to some overflow checks not
triggering when compiling for i386, e.g. when the result of the
calculation didn't overflow in 80bit registers, but did so in 64bit.

While we could just fall back to a non-builtin isinf, it seems likely
that the use of 80bit registers leads to other problems (which is why
we force the flag for GCC already).  Therefore error out when
detecting clang in that situation.

Reported-By: Victor Wagner
Analyzed-By: Andrew Gierth and Andres Freund
Author: Andres Freund
Discussion: https://postgr.es/m/20180905005130.ewk4xcs5dgyzcy45@alap3.anarazel.de
Backpatch: 9.3-, all supported versions are affected
This commit is contained in:
Andres Freund 2018-09-13 14:18:43 -07:00
parent 925673f27b
commit bd1463e348
2 changed files with 51 additions and 0 deletions
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33
configure vendored
View File

@ -7023,6 +7023,39 @@ fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
# Defend against clang being used on x86-32 without SSE2 enabled. As current
# versions of clang do not understand -fexcess-precision=standard, the use of
# x87 floating point operations leads to problems like isinf possibly returning
# false for a value that is infinite when converted from the 80bit register to
# the 8byte memory representation.
#
# Only perform the test if the compiler doesn't understand
# -fexcess-precision=standard, that way a potentially fixed compiler will work
# automatically.
if test "$pgac_cv_prog_CC_cflags__fexcess_precision_standard" = no; then
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int
main ()
{
#if defined(__clang__) && defined(__i386__) && !defined(__SSE2_MATH__)
choke me
#endif
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
else
as_fn_error $? "Compiling PostgreSQL with clang, on 32bit x86, requires SSE2 support. Use -msse2 or use gcc." "$LINENO" 5
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
ac_ext=c
ac_cpp='$CPP $CPPFLAGS'
ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'

18
configure.in
View File

@ -624,6 +624,24 @@ choke me
@%:@endif])], [], [AC_MSG_ERROR([do not put -ffast-math in CFLAGS])])
fi
# Defend against clang being used on x86-32 without SSE2 enabled. As current
# versions of clang do not understand -fexcess-precision=standard, the use of
# x87 floating point operations leads to problems like isinf possibly returning
# false for a value that is infinite when converted from the 80bit register to
# the 8byte memory representation.
#
# Only perform the test if the compiler doesn't understand
# -fexcess-precision=standard, that way a potentially fixed compiler will work
# automatically.
if test "$pgac_cv_prog_CC_cflags__fexcess_precision_standard" = no; then
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
@%:@if defined(__clang__) && defined(__i386__) && !defined(__SSE2_MATH__)
choke me
@%:@endif
])], [],
[AC_MSG_ERROR([Compiling PostgreSQL with clang, on 32bit x86, requires SSE2 support. Use -msse2 or use gcc.])])
fi
AC_PROG_CPP
AC_SUBST(GCC)