[v2] Only build libm with -fno-math-errno
Commit Message
Commit 1294b1892e ("Add support for sqrt asm redirects") added the
-fno-math-errno flag to build most of the glibc in order to enable GCC
to inline math functions. Due to GCC bug #88576, saving and restoring
errno around calls to malloc are optimized-out. In turn this causes
strerror to set errno to ENOMEM if it get passed an invalid error number
and if malloc sets errno to ENOMEM (which might happen even if it
succeeds). This is not allowed by POSIX.
This patch changes the build flags, building only libm with
-fno-math-errno and all the remaining code with -fno-math-errno. This
should be safe as libm doesn't contain any code saving and restoring
errno around malloc. This patch can probably be reverted once the GCC
bug is fixed and available in stable releases.
Tested on x86-64, no regression in the testsuite.
Changelog:
* Makeconfig: Build libm with -fno-math-errno but build the remaining
code with -fmath-errno.
---
ChangeLog | 6 ++++++
Makeconfig | 4 ++--
2 files changed, 8 insertions(+), 2 deletions(-)
v1 -> v2: improved the commit message with a better description of the
issue and the GCC bug number. No code change.
Comments
On Sat, 22 Dec 2018, Aurelien Jarno wrote:
> v1 -> v2: improved the commit message with a better description of the
> issue and the GCC bug number. No code change.
I think the comment, not just the commit message should explain the issue
(i.e., that only libnldbl nonlib testsuite should logically be using
-fmath-errno, but everything apart from libm is currently using
-fmath-errno because of that GCC bug).
(I would say that the comment should give the GCC version in which the bug
is fixed to make it obvious when we can change the code back, but that
doesn't work when the GCC bug isn't yet fixed.)
Could you add a testcase to the testsuite (that appropriately interposes
malloc to demonstrate the bug as in the one attached to the bug, thus
failing before the Makeconfig fix and passing after it)?
@@ -1,3 +1,9 @@
+2018-12-22 Aurelien Jarno <aurelien@aurel32.net>
+
+ [BZ #24024]
+ * Makeconfig: Build libm with -fno-math-errno but build the remaining
+ code with -fmath-errno.
+
2018-12-21 Joseph Myers <joseph@codesourcery.com>
[BZ #24023]
@@ -831,8 +831,8 @@ endif
# disable any optimization that assume default rounding mode.
+math-flags = -frounding-math
-# Build libc/libm using -fno-math-errno, but run testsuite with -fmath-errno.
-+extra-math-flags = $(if $(filter libnldbl nonlib testsuite,$(in-module)),-fmath-errno,-fno-math-errno)
+# Build libm using -fno-math-errno
++extra-math-flags = $(if $(filter libm,$(in-module)),-fno-math-errno,-fmath-errno)
# We might want to compile with some stack-protection flag.
ifneq ($(stack-protector),)