[Bug string/24024] strerror() might set errno to ENOMEM due to -fno-math-error

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https://sourceware.org/bugzilla/show_bug.cgi?id=24024

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=198bfee8085fcc63d6401fec0c542b62aea711a5

commit 198bfee8085fcc63d6401fec0c542b62aea711a5
Author: Aurelien Jarno <aurelien@aurel32.net>
Date:   Thu Jan 3 15:51:37 2019 +0100

    Only build libm with -fno-math-errno (bug 24024)

    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:
        [BZ #24024]
        * Makeconfig: Build libm with -fno-math-errno but build the remaining
        code with -fmath-errno.
        * string/Makefile [$(build-shared)] (tests): Add test-strerror-errno.
        [$(build-shared)] (LDLIBS-test-strerror-errno): New variable.
        * string/test-strerror-errno.c: New file.

    (cherry picked from commit 2ef427168818ce04b03cecb7b739f9db0156e3e4)

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                    |    9 ++++++
 Makeconfig                   |    6 +++-
 NEWS                         |    1 +
 string/Makefile              |    6 ++++
 string/test-strerror-errno.c |   61 ++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 81 insertions(+), 2 deletions(-)
 create mode 100644 string/test-strerror-errno.c

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