* [PATCH] aarch64: fix check for SVE support in assembler
@ 2024-03-14 13:30 Szabolcs Nagy
2024-03-14 13:57 ` Florian Weimer
0 siblings, 1 reply; 3+ messages in thread
From: Szabolcs Nagy @ 2024-03-14 13:30 UTC (permalink / raw)
To: libc-alpha; +Cc: Khem Raj, Ross Burton
Due to GCC bug 110901 -mcpu can override -march setting when compiling
asm code and thus a compiler targetting a specific cpu can fail the
configure check even when binutils gas supports SVE.
The workaround is that explicit .arch directive overrides both -mcpu
and -march, and since that's what the actual SVE memcpy uses the
configure check should use that too even if the GCC issue is fixed
independently.
---
note: i found this in yocto, and i think it's a better fix than
https://git.yoctoproject.org/poky/tree/meta/recipes-core/glibc/glibc/0023-aarch64-configure-Pass-mcpu-along-with-march-to-dete.patch
sysdeps/aarch64/configure | 5 +++--
sysdeps/aarch64/configure.ac | 5 +++--
2 files changed, 6 insertions(+), 4 deletions(-)
mode change 100644 => 100755 sysdeps/aarch64/configure
diff --git a/sysdeps/aarch64/configure b/sysdeps/aarch64/configure
old mode 100644
new mode 100755
index ca57edce47..9606137e8d
--- a/sysdeps/aarch64/configure
+++ b/sysdeps/aarch64/configure
@@ -325,9 +325,10 @@ then :
printf %s "(cached) " >&6
else $as_nop
cat > conftest.s <<\EOF
- ptrue p0.b
+ .arch armv8.2-a+sve
+ ptrue p0.b
EOF
-if { ac_try='${CC-cc} -c -march=armv8.2-a+sve conftest.s 1>&5'
+if { ac_try='${CC-cc} -c conftest.s 1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac
index 27874eceb4..56d12d661d 100644
--- a/sysdeps/aarch64/configure.ac
+++ b/sysdeps/aarch64/configure.ac
@@ -90,9 +90,10 @@ LIBC_CONFIG_VAR([aarch64-variant-pcs], [$libc_cv_aarch64_variant_pcs])
# Check if asm support armv8.2-a+sve
AC_CACHE_CHECK([for SVE support in assembler], [libc_cv_aarch64_sve_asm], [dnl
cat > conftest.s <<\EOF
- ptrue p0.b
+ .arch armv8.2-a+sve
+ ptrue p0.b
EOF
-if AC_TRY_COMMAND(${CC-cc} -c -march=armv8.2-a+sve conftest.s 1>&AS_MESSAGE_LOG_FD); then
+if AC_TRY_COMMAND(${CC-cc} -c conftest.s 1>&AS_MESSAGE_LOG_FD); then
libc_cv_aarch64_sve_asm=yes
else
libc_cv_aarch64_sve_asm=no
--
2.25.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] aarch64: fix check for SVE support in assembler
2024-03-14 13:30 [PATCH] aarch64: fix check for SVE support in assembler Szabolcs Nagy
@ 2024-03-14 13:57 ` Florian Weimer
2024-03-14 17:27 ` Khem Raj
0 siblings, 1 reply; 3+ messages in thread
From: Florian Weimer @ 2024-03-14 13:57 UTC (permalink / raw)
To: Szabolcs Nagy; +Cc: libc-alpha, Khem Raj, Ross Burton
* Szabolcs Nagy:
> Due to GCC bug 110901 -mcpu can override -march setting when compiling
> asm code and thus a compiler targetting a specific cpu can fail the
> configure check even when binutils gas supports SVE.
>
> The workaround is that explicit .arch directive overrides both -mcpu
> and -march, and since that's what the actual SVE memcpy uses the
> configure check should use that too even if the GCC issue is fixed
> independently.
> ---
>
> note: i found this in yocto, and i think it's a better fix than
> https://git.yoctoproject.org/poky/tree/meta/recipes-core/glibc/glibc/0023-aarch64-configure-Pass-mcpu-along-with-march-to-dete.patch
Mechanics look reasonable.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Thanks,
Florian
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] aarch64: fix check for SVE support in assembler
2024-03-14 13:57 ` Florian Weimer
@ 2024-03-14 17:27 ` Khem Raj
0 siblings, 0 replies; 3+ messages in thread
From: Khem Raj @ 2024-03-14 17:27 UTC (permalink / raw)
To: Florian Weimer; +Cc: Szabolcs Nagy, libc-alpha, Ross Burton
On Thu, Mar 14, 2024 at 6:57 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Szabolcs Nagy:
>
> > Due to GCC bug 110901 -mcpu can override -march setting when compiling
> > asm code and thus a compiler targetting a specific cpu can fail the
> > configure check even when binutils gas supports SVE.
> >
> > The workaround is that explicit .arch directive overrides both -mcpu
> > and -march, and since that's what the actual SVE memcpy uses the
> > configure check should use that too even if the GCC issue is fixed
> > independently.
> > ---
> >
> > note: i found this in yocto, and i think it's a better fix than
> > https://git.yoctoproject.org/poky/tree/meta/recipes-core/glibc/glibc/0023-aarch64-configure-Pass-mcpu-along-with-march-to-dete.patch
>
> Mechanics look reasonable.
>
> Reviewed-by: Florian Weimer <fweimer@redhat.com>
LGTM, the yocto patch was just a workaround to wait on GCC to fix the
problem, but this solves is properly within glibc and does not
need to wait on gcc fix. I will test it out.
>
> Thanks,
> Florian
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-03-14 13:30 [PATCH] aarch64: fix check for SVE support in assembler Szabolcs Nagy
2024-03-14 13:57 ` Florian Weimer
2024-03-14 17:27 ` Khem Raj
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