bpo-36618: Add -fmax-type-align=8 flag for clang (GH-12809)
Add -fmax-type-align=8 to CFLAGS when clang compiler is detected.
The pymalloc memory allocator aligns memory on 8 bytes. On x86-64,
clang expects alignment on 16 bytes by default and so uses MOVAPS
instruction which can lead to segmentation fault. Instruct clang that
Python is limited to alignemnt on 8 bytes to use MOVUPS instruction
instead: slower but don't trigger a SIGSEGV if the memory is not
aligned on 16 bytes.
Sadly, the flag must be expected to CFLAGS and not just
CFLAGS_NODIST, since third party C extensions can have the same
issue.
diff --git a/configure b/configure
index 72589fd..ac1e66a 100755
--- a/configure
+++ b/configure
@@ -6813,6 +6813,19 @@
# compiler and platform. BASECFLAGS tweaks need to be made even if the
# user set OPT.
+case $CC in
+ *clang*)
+ cc_is_clang=1
+ ;;
+ *)
+ if $CC --version 2>&1 | grep -q clang
+ then
+ cc_is_clang=1
+ else
+ cc_is_clang=
+ fi
+esac
+
# tweak OPT based on compiler and platform, only if the user didn't set
# it on the command line
@@ -6826,19 +6839,6 @@
WRAP="-fwrapv"
fi
- case $CC in
- *clang*)
- cc_is_clang=1
- ;;
- *)
- if $CC --version 2>&1 | grep -q clang
- then
- cc_is_clang=1
- else
- cc_is_clang=
- fi
- esac
-
if test -n "${cc_is_clang}"
then
# Clang also needs -fwrapv
@@ -6879,6 +6879,21 @@
esac
fi
+if test -n "${cc_is_clang}"
+then
+ # bpo-36618: Add -fmax-type-align=8 to CFLAGS when clang compiler is
+ # detected. The pymalloc memory allocator aligns memory on 8 bytes. On
+ # x86-64, clang expects alignment on 16 bytes by default and so uses MOVAPS
+ # instruction which can lead to segmentation fault. Instruct clang that
+ # Python is limited to alignemnt on 8 bytes to use MOVUPS instruction
+ # instead: slower but don't trigger a SIGSEGV if the memory is not aligned
+ # on 16 bytes.
+ #
+ # Sadly, the flag must be expected to CFLAGS and not just CFLAGS_NODIST,
+ # since third party C extensions can have the same issue.
+ CFLAGS="$CFLAGS -fmax-type-align=8"
+fi
+
@@ -10200,6 +10215,7 @@
+
if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
if test -n "$ac_tool_prefix"; then
# Extract the first word of "${ac_tool_prefix}pkg-config", so it can be a program name with args.