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bpo-30104: Compile dtoa.c without strict aliasing #1340

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Merged
vstinner merged 1 commit into from
Apr 28, 2017
Merged

bpo-30104: Compile dtoa.c without strict aliasing #1340

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9 changes: 9 additions & 0 deletions Makefile.pre.in
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,8 @@ ARFLAGS= @ARFLAGS@
CFLAGSFORSHARED=@CFLAGSFORSHARED@
# C flags used for building the interpreter object files
PY_CORE_CFLAGS= $(PY_CFLAGS) $(PY_CFLAGS_NODIST) $(PY_CPPFLAGS) $(CFLAGSFORSHARED) -DPy_BUILD_CORE
# Strict or non-strict aliasing flags used to compile dtoa.c, see above
CFLAGS_ALIASING=@CFLAGS_ALIASING@


# Machine-dependent subdirectories
Expand Down Expand Up @@ -1536,6 +1538,13 @@ config.status: $(srcdir)/configure
.c.o:
$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<

# bpo-30104: dtoa.c uses union to cast double to unsigned long[2]. clang 4.0
# with -O2 or higher and strict aliasing miscompiles the ratio() function
# causing rounding issues. Compile dtoa.c using -fno-strict-aliasing on clang.
# https://bugs.llvm.org//show_bug.cgi?id=31928
Python/dtoa.o: Python/dtoa.c
$(CC) -c $(PY_CORE_CFLAGS) $(CFLAGS_ALIASING) -o $@ $<

# Run reindent on the library
reindent:
./$(BUILDPYTHON) $(srcdir)/Tools/scripts/reindent.py -r $(srcdir)/Lib
Expand Down
11 changes: 3 additions & 8 deletions configure
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Expand Up @@ -668,6 +668,7 @@ OTHER_LIBTOOL_OPT
UNIVERSAL_ARCH_FLAGS
CFLAGS_NODIST
BASECFLAGS
CFLAGS_ALIASING
OPT
LLVM_PROF_FOUND
target_os
Expand Down Expand Up @@ -6829,13 +6830,7 @@ then
then
# Clang also needs -fwrapv
WRAP="-fwrapv"

# bpo-30104: Python/dtoa.c requires to be build with
# -fno-strict-aliasing to fix compiler issue on the
# double/ULong[2] union using clang 4.0 and optimization level
# -O2 or higher
# https://bugs.llvm.org//show_bug.cgi?id=31928
ALIASING="-fno-strict-aliasing"
CFLAGS_ALIASING="-fno-strict-aliasing"
fi

case $ac_cv_prog_cc_g in
Expand All @@ -6857,7 +6852,7 @@ then
;;
esac

OPT="$OPT $STRICT_PROTO $ALIASING"
OPT="$OPT $STRICT_PROTO"

case $ac_sys_system in
SCO_SV*) OPT="$OPT -m486 -DSCO5"
Expand Down
13 changes: 5 additions & 8 deletions configure.ac
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Expand Up @@ -1440,6 +1440,7 @@ esac
# tweak OPT based on compiler and platform, only if the user didn't set
# it on the command line
AC_SUBST(OPT)
AC_SUBST(CFLAGS_ALIASING)
if test "${OPT-unset}" = "unset"
then
case $GCC in
Expand Down Expand Up @@ -1469,13 +1470,9 @@ then
then
# Clang also needs -fwrapv
WRAP="-fwrapv"

# bpo-30104: Python/dtoa.c requires to be build with
# -fno-strict-aliasing to fix compiler issue on the
# double/ULong[2] union using clang 4.0 and optimization level
# -O2 or higher
# https://bugs.llvm.org//show_bug.cgi?id=31928
ALIASING="-fno-strict-aliasing"
# bpo-30104: disable strict aliasing to compile correctly dtoa.c,
# see Makefile.pre.in for more information
CFLAGS_ALIASING="-fno-strict-aliasing"
fi

case $ac_cv_prog_cc_g in
Expand All @@ -1497,7 +1494,7 @@ then
;;
esac

OPT="$OPT $STRICT_PROTO $ALIASING"
OPT="$OPT $STRICT_PROTO"

case $ac_sys_system in
SCO_SV*) OPT="$OPT -m486 -DSCO5"
Expand Down