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sys-libs/glibc: Add stack-realign flag for compat with old 32-bit x86 binaries

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Older 32-bit x86 binaries aligned the stack to 4 bytes, whereas modern
binaries align to 16 bytes. These older binaries sometimes segfault when
newer libraries use SSE instructions. This is becoming increasingly
common. Applying the -mstackrealign flag to the 32-bit build works
around the issue but at a performance cost. Other popular
distributions always apply this.

[sam: There's no good choices here. As Ionen pointed out (I'd missed
any reports of this), this ends up getting worse with GCC 12's
default-on vectorisation at -O2. Let's make it optional for now for
32-bit/x86 (irrelevant for other arches, it's specific to x86 ABI).

ncurses is going to need similar treatment. If we end up having
to do this for far more packages, we may revisit and e.g.
just append-flags in ebuilds for right ABI and tell users
to set -mno-stackrealign, or similar.

Another option would be to set this globally by default (again,
this is only ever for x86), but it'd possibly be a big performance
hit (and bad enough doing it in glibc, but it's unavoidable).

The only saving grace here is that there aren't _that_ many
libraries with such longevity & ABI stability from back then
that older applications are using.]

Bug: https://bugs.gentoo.org/616402
Bug: https://github.com/taviso/123elf/issues/12
Signed-off-by: James Le Cuirot <chewi@gentoo.org>
Closes: https://github.com/gentoo/gentoo/pull/25858
Signed-off-by: Sam James <sam@gentoo.org>
This commit is contained in:
James Le Cuirot
2022-06-25 22:39:28 +01:00
committed by Sam James
parent 7e5859b42a
commit 02aa6328a7
3 changed files with 37 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files
sys-libs/glibc/glibc-2.35-r7.ebuild
+18 -13
View File
@@ -44,7 +44,7 @@ SRC_URI+=" https://gitweb.gentoo.org/proj/locale-gen.git/snapshot/locale-gen-${L
SRC_URI+=" multilib-bootstrap? ( https://dev.gentoo.org/~dilfridge/distfiles/gcc-multilib-bootstrap-${GCC_BOOTSTRAP_VER}.tar.xz )"
SRC_URI+=" systemd? ( https://gitweb.gentoo.org/proj/toolchain/glibc-systemd.git/snapshot/glibc-systemd-${GLIBC_SYSTEMD_VER}.tar.gz )"
IUSE="audit caps cet +clone3 compile-locales +crypt custom-cflags doc experimental-loong gd headers-only +multiarch multilib multilib-bootstrap nscd profile selinux +ssp +static-libs suid systemd systemtap test vanilla"
IUSE="audit caps cet +clone3 compile-locales +crypt custom-cflags doc experimental-loong gd headers-only +multiarch multilib multilib-bootstrap nscd profile selinux +ssp stack-realign +static-libs suid systemd systemtap test vanilla"
# Minimum kernel version that glibc requires
MIN_KERN_VER="3.2.0"
@@ -305,22 +305,27 @@ setup_target_flags() {
export CFLAGS="-march=${t} ${CFLAGS}"
einfo "Auto adding -march=${t} to CFLAGS #185404"
fi
# For compatibility with older binaries at slight performance cost.
use stack-realign && export CFLAGS+=" -mstackrealign"
;;
amd64)
# -march needed for #185404 #199334
# TODO: See cross-compile issues listed above for x86.
[[ ${ABI} == x86 ]] &&
if ! do_compile_test "${CFLAGS_x86}" 'void f(int i, void *p) {if (__sync_fetch_and_add(&i, 1)) f(i, p);}\nint main(){return 0;}\n'; then
local t=${CTARGET_OPT:-${CTARGET}}
t=${t%%-*}
# Normally the target is x86_64-xxx, so turn that into the -march that
# gcc actually accepts. #528708
[[ ${t} == "x86_64" ]] && t="x86-64"
filter-flags '-march=*'
# ugly, ugly, ugly. ugly.
CFLAGS_x86=$(CFLAGS=${CFLAGS_x86} filter-flags '-march=*'; echo "${CFLAGS}")
export CFLAGS_x86="${CFLAGS_x86} -march=${t}"
einfo "Auto adding -march=${t} to CFLAGS_x86 #185404 (ABI=${ABI})"
if [[ ${ABI} == x86 ]]; then
if ! do_compile_test "${CFLAGS_x86}" 'void f(int i, void *p) {if (__sync_fetch_and_add(&i, 1)) f(i, p);}\nint main(){return 0;}\n'; then
local t=${CTARGET_OPT:-${CTARGET}}
t=${t%%-*}
# Normally the target is x86_64-xxx, so turn that into the -march that
# gcc actually accepts. #528708
[[ ${t} == "x86_64" ]] && t="x86-64"
filter-flags '-march=*'
# ugly, ugly, ugly. ugly.
CFLAGS_x86=$(CFLAGS=${CFLAGS_x86} filter-flags '-march=*'; echo "${CFLAGS}")
export CFLAGS_x86="${CFLAGS_x86} -march=${t}"
einfo "Auto adding -march=${t} to CFLAGS_x86 #185404 (ABI=${ABI})"
fi
# For compatibility with older binaries at slight performance cost.
use stack-realign && export CFLAGS_x86+=" -mstackrealign"
fi
;;
mips)
sys-libs/glibc/glibc-9999.ebuild
+18 -13
View File
@@ -44,7 +44,7 @@ SRC_URI+=" https://gitweb.gentoo.org/proj/locale-gen.git/snapshot/locale-gen-${L
SRC_URI+=" multilib-bootstrap? ( https://dev.gentoo.org/~dilfridge/distfiles/gcc-multilib-bootstrap-${GCC_BOOTSTRAP_VER}.tar.xz )"
SRC_URI+=" systemd? ( https://gitweb.gentoo.org/proj/toolchain/glibc-systemd.git/snapshot/glibc-systemd-${GLIBC_SYSTEMD_VER}.tar.gz )"
IUSE="audit caps cet compile-locales +crypt custom-cflags doc gd headers-only +multiarch multilib multilib-bootstrap nscd profile selinux +ssp +static-libs suid systemd systemtap test vanilla"
IUSE="audit caps cet compile-locales +crypt custom-cflags doc gd headers-only +multiarch multilib multilib-bootstrap nscd profile selinux +ssp stack-realign +static-libs suid systemd systemtap test vanilla"
# Minimum kernel version that glibc requires
MIN_KERN_VER="3.2.0"
@@ -305,22 +305,27 @@ setup_target_flags() {
export CFLAGS="-march=${t} ${CFLAGS}"
einfo "Auto adding -march=${t} to CFLAGS #185404"
fi
# For compatibility with older binaries at slight performance cost.
use stack-realign && export CFLAGS+=" -mstackrealign"
;;
amd64)
# -march needed for #185404 #199334
# TODO: See cross-compile issues listed above for x86.
[[ ${ABI} == x86 ]] &&
if ! do_compile_test "${CFLAGS_x86}" 'void f(int i, void *p) {if (__sync_fetch_and_add(&i, 1)) f(i, p);}\nint main(){return 0;}\n'; then
local t=${CTARGET_OPT:-${CTARGET}}
t=${t%%-*}
# Normally the target is x86_64-xxx, so turn that into the -march that
# gcc actually accepts. #528708
[[ ${t} == "x86_64" ]] && t="x86-64"
filter-flags '-march=*'
# ugly, ugly, ugly. ugly.
CFLAGS_x86=$(CFLAGS=${CFLAGS_x86} filter-flags '-march=*'; echo "${CFLAGS}")
export CFLAGS_x86="${CFLAGS_x86} -march=${t}"
einfo "Auto adding -march=${t} to CFLAGS_x86 #185404 (ABI=${ABI})"
if [[ ${ABI} == x86 ]]; then
if ! do_compile_test "${CFLAGS_x86}" 'void f(int i, void *p) {if (__sync_fetch_and_add(&i, 1)) f(i, p);}\nint main(){return 0;}\n'; then
local t=${CTARGET_OPT:-${CTARGET}}
t=${t%%-*}
# Normally the target is x86_64-xxx, so turn that into the -march that
# gcc actually accepts. #528708
[[ ${t} == "x86_64" ]] && t="x86-64"
filter-flags '-march=*'
# ugly, ugly, ugly. ugly.
CFLAGS_x86=$(CFLAGS=${CFLAGS_x86} filter-flags '-march=*'; echo "${CFLAGS}")
export CFLAGS_x86="${CFLAGS_x86} -march=${t}"
einfo "Auto adding -march=${t} to CFLAGS_x86 #185404 (ABI=${ABI})"
fi
# For compatibility with older binaries at slight performance cost.
use stack-realign && export CFLAGS_x86+=" -mstackrealign"
fi
;;
mips)
sys-libs/glibc/metadata.xml
+1
View File
@@ -17,6 +17,7 @@
<flag name="multilib-bootstrap">Provide prebuilt libgcc.a and crt files if missing. Only needed for ABI switch.</flag>
<flag name="nscd">Build, and enable support for, the Name Service Cache Daemon</flag>
<flag name="ssp">protect stack of glibc internals</flag>
<flag name="stack-realign">Realign the stack in the 32-bit build for compatibility with older binaries at slight performance cost</flag>
<flag name="static-pie">Enable static PIE support (runtime files for -static-pie gcc option).</flag>
<flag name="suid">Make internal pt_chown helper setuid -- not needed if using Linux and have /dev/pts mounted with gid=5</flag>
<flag name="systemtap">enable systemtap static probe points</flag>