path: root/configure
diff options
authorRich Felker <>2014-07-16 21:32:06 -0400
committerRich Felker <>2014-07-16 21:32:06 -0400
commita6adb2bcd8145353943377d6119c1d7a4242bae1 (patch)
tree0ea88fa60243c6ac696917cbb4264da0f59b786b /configure
parentc463e11eda8326aacee2ac1d516954a9574a2dcd (diff)
work around constant folding bug 61144 in gcc 4.9.0 and 4.9.1
previously we detected this bug in configure and issued advice for a workaround, but this turned out not to work. since then gcc 4.9.0 has appeared in several distributions, and now 4.9.1 has been released without a fix despite this being a wrong code generation bug which is supposed to be a release-blocker, per gcc policy. since the scope of the bug seems to affect only data objects (rather than functions) whose definitions are overridable, and there are only a very small number of these in musl, I am just changing them from const to volatile for the time being. simply removing the const would be sufficient to make gcc 4.9.1 work (the non-const case was inadvertently fixed as part of another change in gcc), and this would also be sufficient with 4.9.0 if we forced -O0 on the affected files or on the whole build. however it's cleaner to just remove all the broken compiler detection and use volatile, which will ensure that they are never constant-folded. the quality of a non-broken compiler's output should not be affected except for the fact that these objects are no longer const and thus possibly add a few bytes to data/bss. this change can be reconsidered and possibly reverted at some point in the future when the broken gcc versions are no longer relevant.
Diffstat (limited to 'configure')
1 files changed, 0 insertions, 21 deletions
diff --git a/configure b/configure
index b1cf9980..7436210f 100755
--- a/configure
+++ b/configure
@@ -495,27 +495,6 @@ printf "no\n"
fail "$0: error: unsupported long double type"
-# Check for known bug in GCC 4.9.0 that results in a broken libc.
-if test "$cc_is_gcc" = yes ; then
-printf "checking for gcc constant folding bug with weak aliases... "
-echo 'static int x = 0;' > "$tmpc"
-echo 'extern int y __attribute__((__weak__, __alias__("x")));' >> "$tmpc"
-echo 'extern int should_appear;' >> "$tmpc"
-echo 'int foo() { return y ? should_appear : 0; }' >> "$tmpc"
-case "$($CC $CFLAGS_C99FSE -I./arch/$ARCH -I./include \
- $CPPFLAGS $CFLAGS_AUTO $CFLAGS -S -o - "$tmpc" 2>/dev/null)" in
-printf "no\n"
-printf "yes\n"
-fail "$0: error: broken compiler; try CFLAGS=-fno-toplevel-reorder"
printf "creating config.mak... "
cmdline=$(quote "$0")