* glibc-hwcaps for armv7 (neon-vfpv4)
@ 2023-08-31 10:06 Mathieu Malaterre
2023-08-31 11:24 ` Florian Weimer
0 siblings, 1 reply; 6+ messages in thread
From: Mathieu Malaterre @ 2023-08-31 10:06 UTC (permalink / raw)
To: libc-help
Dear glibc maintainer,
I fail to understand the ld.so man page (Debian/sid version: man-pages
6.03) for hwcaps support. Specifically I'd like to install a shared
lib on a Debian/armhf system (baseline is neon-less) which was build
with gcc option:
-march=armv7-a -mfpu=neon-vfpv4
What subfolder should I be using ?
Thanks,
--
Conversely how should I read the following:
% sudo ldconfig -p | grep hwcap
libfoo.so.160 (libc6,x86-64, hwcap: 0x0004000000000000) =>
/lib/x86_64-linux-gnu/haswell/libfoo.so.160
libfoo.so.160 (libc6,x86-64, hwcap: 0x0000000000000004) =>
/lib/x86_64-linux-gnu/avx512_1/libfoo.so.160
What does "haswell" / "avx512_1" subfolder implies in terms of gcc
compile options ?
Thanks (again)
-M
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: glibc-hwcaps for armv7 (neon-vfpv4)
2023-08-31 10:06 glibc-hwcaps for armv7 (neon-vfpv4) Mathieu Malaterre
@ 2023-08-31 11:24 ` Florian Weimer
2023-08-31 12:08 ` Mathieu Malaterre
0 siblings, 1 reply; 6+ messages in thread
From: Florian Weimer @ 2023-08-31 11:24 UTC (permalink / raw)
To: Mathieu Malaterre; +Cc: libc-help
* Mathieu Malaterre:
> Dear glibc maintainer,
>
> I fail to understand the ld.so man page (Debian/sid version: man-pages
> 6.03) for hwcaps support. Specifically I'd like to install a shared
> lib on a Debian/armhf system (baseline is neon-less) which was build
> with gcc option:
>
> -march=armv7-a -mfpu=neon-vfpv4
>
> What subfolder should I be using ?
You can use “LD_LIBRARY_PATH=. /bin/true” to see which subdirectories
are probed. I think either neon/vfp or vfp/neon should be among the
subdirectories. This functionality has since been removed from upstream
glibc because it sometimes results in hundereds of extra openat system
calls.
> Conversely how should I read the following:
>
> % sudo ldconfig -p | grep hwcap
> libfoo.so.160 (libc6,x86-64, hwcap: 0x0004000000000000) =>
> /lib/x86_64-linux-gnu/haswell/libfoo.so.160
> libfoo.so.160 (libc6,x86-64, hwcap: 0x0000000000000004) =>
> /lib/x86_64-linux-gnu/avx512_1/libfoo.so.160
>
> What does "haswell" / "avx512_1" subfolder implies in terms of gcc
> compile options ?
It's complicated. Nowdays, on x86-64, you can use
glibc-hwcaps/x86-64-v3 and glibc-hwcaps/x86-64-v4, which are designed to
correspond to -march=x86-64-v3 and -march=x86-64-v4, and x86-64-v4 is a
superset of x86-64-v3.
Thanks,
Florian
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: glibc-hwcaps for armv7 (neon-vfpv4)
2023-08-31 11:24 ` Florian Weimer
@ 2023-08-31 12:08 ` Mathieu Malaterre
2023-08-31 15:30 ` Adhemerval Zanella Netto
2023-08-31 17:20 ` Florian Weimer
0 siblings, 2 replies; 6+ messages in thread
From: Mathieu Malaterre @ 2023-08-31 12:08 UTC (permalink / raw)
To: Florian Weimer; +Cc: libc-help
Hi Florian !
On Thu, Aug 31, 2023 at 1:24 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Mathieu Malaterre:
>
> > Dear glibc maintainer,
> >
> > I fail to understand the ld.so man page (Debian/sid version: man-pages
> > 6.03) for hwcaps support. Specifically I'd like to install a shared
> > lib on a Debian/armhf system (baseline is neon-less) which was build
> > with gcc option:
> >
> > -march=armv7-a -mfpu=neon-vfpv4
> >
> > What subfolder should I be using ?
>
> You can use “LD_LIBRARY_PATH=. /bin/true” to see which subdirectories
> are probed. I think either neon/vfp or vfp/neon should be among the
> subdirectories. This functionality has since been removed from upstream
> glibc because it sometimes results in hundereds of extra openat system
> calls.
oh, thanks for the trick. Could you confirm my conclusion below
(Debian/i386 sid system):
% file /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164
/usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164: ELF 32-bit LSB
shared object, Intel 80386, version 1 (SYSV), dynamically linked,
BuildID[sha1]=e66974d10aef77af7ed504266cde974d103484d6, stripped
However:
% /sbin/ldconfig -v 2>/dev/null | grep -A3 hwcap
-> nothing
same goes with:
% LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
3327956: find library=libc.so.6 [0]; searching
3327956: search path=. (LD_LIBRARY_PATH)
3327956: trying file=./libc.so.6
3327956: search cache=/etc/ld.so.cache
3327956: trying file=/lib/i386-linux-gnu/libc.so.6
3327956:
3327956:
3327956: calling init: /lib/ld-linux.so.2
3327956:
3327956:
3327956: calling init: /lib/i386-linux-gnu/libc.so.6
3327956:
3327956:
3327956: initialize program: /bin/true
3327956:
3327956:
3327956: transferring control: /bin/true
3327956:
3327956:
3327956: calling fini: [0]
3327956:
3327956:
3327956: calling fini: /lib/i386-linux-gnu/libc.so.6 [0]
3327956:
3327956:
3327956: calling fini: /lib/ld-linux.so.2 [0]
3327956:
If I understand correctly the file
/usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164 cannot be used on
Debian/sid/i386 system since libc used is:
% /lib/i386-linux-gnu/libc.so.6
GNU C Library (Debian GLIBC 2.37-7) stable release version 2.37.
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 12.3.0.
libc ABIs: UNIQUE IFUNC ABSOLUTE
Minimum supported kernel: 3.2.0
For bug reporting instructions, please see:
<http://www.debian.org/Bugs/>.
> > Conversely how should I read the following:
> >
> > % sudo ldconfig -p | grep hwcap
> > libfoo.so.160 (libc6,x86-64, hwcap: 0x0004000000000000) =>
> > /lib/x86_64-linux-gnu/haswell/libfoo.so.160
> > libfoo.so.160 (libc6,x86-64, hwcap: 0x0000000000000004) =>
> > /lib/x86_64-linux-gnu/avx512_1/libfoo.so.160
> >
> > What does "haswell" / "avx512_1" subfolder implies in terms of gcc
> > compile options ?
>
> It's complicated. Nowdays, on x86-64, you can use
> glibc-hwcaps/x86-64-v3 and glibc-hwcaps/x86-64-v4, which are designed to
> correspond to -march=x86-64-v3 and -march=x86-64-v4, and x86-64-v4 is a
> superset of x86-64-v3.
Ok, thanks for the update.
Could you just review what I see on my Debian/sid/armhf system:
% cat /proc/cpuinfo | grep Features | uniq
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4
idiva idivt lpae evtstrm
% LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
2964957: find library=libc.so.6 [0]; searching
2964957: search path=. (LD_LIBRARY_PATH)
2964957: trying file=./libc.so.6
2964957: search cache=/etc/ld.so.cache
2964957: trying file=/lib/arm-linux-gnueabihf/libc.so.6
2964957:
2964957:
2964957: calling init: /lib/ld-linux-armhf.so.3
2964957:
2964957:
2964957: calling init: /lib/arm-linux-gnueabihf/libc.so.6
2964957:
2964957:
2964957: initialize program: /bin/true
2964957:
2964957:
2964957: transferring control: /bin/true
2964957:
2964957:
2964957: calling fini: [0]
2964957:
2964957:
2964957: calling fini: /lib/arm-linux-gnueabihf/libc.so.6 [0]
2964957:
2964957:
2964957: calling fini: /lib/ld-linux-armhf.so.3 [0]
2964957:
Based on the above, it seems glibc is setup to never search hwcaps
optimized libraries on this system (even if neon/vfpv4 is supported by
system).
Thanks again for your kind help
-M
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: glibc-hwcaps for armv7 (neon-vfpv4)
2023-08-31 12:08 ` Mathieu Malaterre
@ 2023-08-31 15:30 ` Adhemerval Zanella Netto
2023-09-01 7:18 ` Mathieu Malaterre
2023-08-31 17:20 ` Florian Weimer
1 sibling, 1 reply; 6+ messages in thread
From: Adhemerval Zanella Netto @ 2023-08-31 15:30 UTC (permalink / raw)
To: Mathieu Malaterre, Florian Weimer; +Cc: libc-help
On 31/08/23 09:08, Mathieu Malaterre wrote:
> Hi Florian !
>
> On Thu, Aug 31, 2023 at 1:24 PM Florian Weimer <fweimer@redhat.com> wrote:
>>
>> * Mathieu Malaterre:
>>
>>> Dear glibc maintainer,
>>>
>>> I fail to understand the ld.so man page (Debian/sid version: man-pages
>>> 6.03) for hwcaps support. Specifically I'd like to install a shared
>>> lib on a Debian/armhf system (baseline is neon-less) which was build
>>> with gcc option:
>>>
>>> -march=armv7-a -mfpu=neon-vfpv4
>>>
>>> What subfolder should I be using ?
>>
>> You can use “LD_LIBRARY_PATH=. /bin/true” to see which subdirectories
>> are probed. I think either neon/vfp or vfp/neon should be among the
>> subdirectories. This functionality has since been removed from upstream
>> glibc because it sometimes results in hundereds of extra openat system
>> calls.
>
> oh, thanks for the trick. Could you confirm my conclusion below
> (Debian/i386 sid system):
>
> % file /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164
> /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164: ELF 32-bit LSB
> shared object, Intel 80386, version 1 (SYSV), dynamically linked,
> BuildID[sha1]=e66974d10aef77af7ed504266cde974d103484d6, stripped
>
> However:
>
> % /sbin/ldconfig -v 2>/dev/null | grep -A3 hwcap
> -> nothing
>
> same goes with:
>
> % LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
> 3327956: find library=libc.so.6 [0]; searching
> 3327956: search path=. (LD_LIBRARY_PATH)
> 3327956: trying file=./libc.so.6
> 3327956: search cache=/etc/ld.so.cache
> 3327956: trying file=/lib/i386-linux-gnu/libc.so.6
> 3327956:
> 3327956:
> 3327956: calling init: /lib/ld-linux.so.2
> 3327956:
> 3327956:
> 3327956: calling init: /lib/i386-linux-gnu/libc.so.6
> 3327956:
> 3327956:
> 3327956: initialize program: /bin/true
> 3327956:
> 3327956:
> 3327956: transferring control: /bin/true
> 3327956:
> 3327956:
> 3327956: calling fini: [0]
> 3327956:
> 3327956:
> 3327956: calling fini: /lib/i386-linux-gnu/libc.so.6 [0]
> 3327956:
> 3327956:
> 3327956: calling fini: /lib/ld-linux.so.2 [0]
> 3327956:
>
>
> If I understand correctly the file
> /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164 cannot be used on
> Debian/sid/i386 system since libc used is:
>
> % /lib/i386-linux-gnu/libc.so.6
> GNU C Library (Debian GLIBC 2.37-7) stable release version 2.37.
> Copyright (C) 2023 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.
> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
> PARTICULAR PURPOSE.
> Compiled by GNU CC version 12.3.0.
> libc ABIs: UNIQUE IFUNC ABSOLUTE
> Minimum supported kernel: 3.2.0
> For bug reporting instructions, please see:
> <http://www.debian.org/Bugs/>.
From your system configuration, it seems so. On a ubuntu22 I see:
$ find /usr/ -iname libx264.so*
/usr/lib/i386-linux-gnu/libx264.so.163
/usr/lib/i386-linux-gnu/i686/sse2/libx264.so.163
/usr/lib/x86_64-linux-gnu/libx264.so.163
$ /sbin/ldconfig -v 2>/dev/null | grep -A3 hwcap
/lib/i386-linux-gnu/i686: (hwcap: 0x0002000000000000) (from /etc/ld.so.conf.d/i386-linux-gnu.conf:3)
/lib/i386-linux-gnu/i686/sse2: (hwcap: 0x0002000000000001) (from /etc/ld.so.conf.d/i386-linux-gnu.conf:3)
libx264.so.163 -> libx264.so.163
$ cat /etc/ld.so.conf.d/i386-linux-gnu.conf
# Multiarch support
/usr/local/lib/i386-linux-gnu
/lib/i386-linux-gnu
/usr/lib/i386-linux-gnu
/usr/local/lib/i686-linux-gnu
/lib/i686-linux-gnu
/usr/lib/i686-linux-gnu
$ /lib/ld-linux.so.2 --help
[...]
Shared library search path:
(libraries located via /etc/ld.so.cache)
/lib/i386-linux-gnu (system search path)
/usr/lib/i386-linux-gnu (system search path)
/lib (system search path)
/usr/lib (system search path)
No subdirectories of glibc-hwcaps directories are searched.
Legacy HWCAP subdirectories under library search path directories:
i686 (AT_PLATFORM; supported, searched)
tls (supported, searched)
sse2 (supported, searched)
So if you have '/usr/lib/i386-linux-gnu' add on your ld.so.cache, the
<path>/i686/see will be search through legacy hwcap support.
>
>>> Conversely how should I read the following:
>>>
>>> % sudo ldconfig -p | grep hwcap
>>> libfoo.so.160 (libc6,x86-64, hwcap: 0x0004000000000000) =>
>>> /lib/x86_64-linux-gnu/haswell/libfoo.so.160
>>> libfoo.so.160 (libc6,x86-64, hwcap: 0x0000000000000004) =>
>>> /lib/x86_64-linux-gnu/avx512_1/libfoo.so.160
>>>
>>> What does "haswell" / "avx512_1" subfolder implies in terms of gcc
>>> compile options ?
>>
>> It's complicated. Nowdays, on x86-64, you can use
>> glibc-hwcaps/x86-64-v3 and glibc-hwcaps/x86-64-v4, which are designed to
>> correspond to -march=x86-64-v3 and -march=x86-64-v4, and x86-64-v4 is a
>> superset of x86-64-v3.
>
> Ok, thanks for the update.
>
> Could you just review what I see on my Debian/sid/armhf system:
>
> % cat /proc/cpuinfo | grep Features | uniq
> Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4
> idiva idivt lpae evtstrm
> % LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
> 2964957: find library=libc.so.6 [0]; searching
> 2964957: search path=. (LD_LIBRARY_PATH)
> 2964957: trying file=./libc.so.6
> 2964957: search cache=/etc/ld.so.cache
> 2964957: trying file=/lib/arm-linux-gnueabihf/libc.so.6
> 2964957:
> 2964957:
> 2964957: calling init: /lib/ld-linux-armhf.so.3
> 2964957:
> 2964957:
> 2964957: calling init: /lib/arm-linux-gnueabihf/libc.so.6
> 2964957:
> 2964957:
> 2964957: initialize program: /bin/true
> 2964957:
> 2964957:
> 2964957: transferring control: /bin/true
> 2964957:
> 2964957:
> 2964957: calling fini: [0]
> 2964957:
> 2964957:
> 2964957: calling fini: /lib/arm-linux-gnueabihf/libc.so.6 [0]
> 2964957:
> 2964957:
> 2964957: calling fini: /lib/ld-linux-armhf.so.3 [0]
> 2964957:
>
> Based on the above, it seems glibc is setup to never search hwcaps
> optimized libraries on this system (even if neon/vfpv4 is supported by
> system).
This is a ubuntu22 armhf chroot on aarch64:
$ /lib/ld-linux-armhf.so.3 --help
[...]
Shared library search path:
(libraries located via /etc/ld.so.cache)
/lib/arm-linux-gnueabihf (system search path)
/usr/lib/arm-linux-gnueabihf (system search path)
/lib (system search path)
/usr/lib (system search path)
No subdirectories of glibc-hwcaps directories are searched.
Legacy HWCAP subdirectories under library search path directories:
v8l (AT_PLATFORM; supported, searched)
tls (supported, searched)
neon (supported, searched)
vfp (supported, searched)
So both neon and vfp; I can not say exactly how debian is configured since both
ubuntu and debian carry out of tree patches; but I would expect them to be
similar regarding libc.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: glibc-hwcaps for armv7 (neon-vfpv4)
2023-08-31 12:08 ` Mathieu Malaterre
2023-08-31 15:30 ` Adhemerval Zanella Netto
@ 2023-08-31 17:20 ` Florian Weimer
1 sibling, 0 replies; 6+ messages in thread
From: Florian Weimer @ 2023-08-31 17:20 UTC (permalink / raw)
To: Mathieu Malaterre; +Cc: libc-help
* Mathieu Malaterre:
> If I understand correctly the file
> /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164 cannot be used on
> Debian/sid/i386 system since libc used is:
>
> % /lib/i386-linux-gnu/libc.so.6
> GNU C Library (Debian GLIBC 2.37-7) stable release version 2.37.
> Copyright (C) 2023 Free Software Foundation, Inc.
Yes, glibc 2.37 was the first upstream version that removed aggressive
HWCAP subdirectory probing.
Thanks,
Florian
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: glibc-hwcaps for armv7 (neon-vfpv4)
2023-08-31 15:30 ` Adhemerval Zanella Netto
@ 2023-09-01 7:18 ` Mathieu Malaterre
0 siblings, 0 replies; 6+ messages in thread
From: Mathieu Malaterre @ 2023-09-01 7:18 UTC (permalink / raw)
To: Adhemerval Zanella Netto; +Cc: Florian Weimer, libc-help
Hi !
On Thu, Aug 31, 2023 at 5:30 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 31/08/23 09:08, Mathieu Malaterre wrote:
> > Hi Florian !
> >
> > On Thu, Aug 31, 2023 at 1:24 PM Florian Weimer <fweimer@redhat.com> wrote:
> >>
> >> * Mathieu Malaterre:
> >>
> >>> Dear glibc maintainer,
> >>>
> >>> I fail to understand the ld.so man page (Debian/sid version: man-pages
> >>> 6.03) for hwcaps support. Specifically I'd like to install a shared
> >>> lib on a Debian/armhf system (baseline is neon-less) which was build
> >>> with gcc option:
> >>>
> >>> -march=armv7-a -mfpu=neon-vfpv4
> >>>
> >>> What subfolder should I be using ?
> >>
> >> You can use “LD_LIBRARY_PATH=. /bin/true” to see which subdirectories
> >> are probed. I think either neon/vfp or vfp/neon should be among the
> >> subdirectories. This functionality has since been removed from upstream
> >> glibc because it sometimes results in hundereds of extra openat system
> >> calls.
> >
> > oh, thanks for the trick. Could you confirm my conclusion below
> > (Debian/i386 sid system):
> >
> > % file /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164
> > /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164: ELF 32-bit LSB
> > shared object, Intel 80386, version 1 (SYSV), dynamically linked,
> > BuildID[sha1]=e66974d10aef77af7ed504266cde974d103484d6, stripped
> >
> > However:
> >
> > % /sbin/ldconfig -v 2>/dev/null | grep -A3 hwcap
> > -> nothing
> >
> > same goes with:
> >
> > % LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
> > 3327956: find library=libc.so.6 [0]; searching
> > 3327956: search path=. (LD_LIBRARY_PATH)
> > 3327956: trying file=./libc.so.6
> > 3327956: search cache=/etc/ld.so.cache
> > 3327956: trying file=/lib/i386-linux-gnu/libc.so.6
> > 3327956:
> > 3327956:
> > 3327956: calling init: /lib/ld-linux.so.2
> > 3327956:
> > 3327956:
> > 3327956: calling init: /lib/i386-linux-gnu/libc.so.6
> > 3327956:
> > 3327956:
> > 3327956: initialize program: /bin/true
> > 3327956:
> > 3327956:
> > 3327956: transferring control: /bin/true
> > 3327956:
> > 3327956:
> > 3327956: calling fini: [0]
> > 3327956:
> > 3327956:
> > 3327956: calling fini: /lib/i386-linux-gnu/libc.so.6 [0]
> > 3327956:
> > 3327956:
> > 3327956: calling fini: /lib/ld-linux.so.2 [0]
> > 3327956:
> >
> >
> > If I understand correctly the file
> > /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.164 cannot be used on
> > Debian/sid/i386 system since libc used is:
> >
> > % /lib/i386-linux-gnu/libc.so.6
> > GNU C Library (Debian GLIBC 2.37-7) stable release version 2.37.
> > Copyright (C) 2023 Free Software Foundation, Inc.
> > This is free software; see the source for copying conditions.
> > There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
> > PARTICULAR PURPOSE.
> > Compiled by GNU CC version 12.3.0.
> > libc ABIs: UNIQUE IFUNC ABSOLUTE
> > Minimum supported kernel: 3.2.0
> > For bug reporting instructions, please see:
> > <http://www.debian.org/Bugs/>.
>
> From your system configuration, it seems so. On a ubuntu22 I see:
>
> $ find /usr/ -iname libx264.so*
> /usr/lib/i386-linux-gnu/libx264.so.163
> /usr/lib/i386-linux-gnu/i686/sse2/libx264.so.163
> /usr/lib/x86_64-linux-gnu/libx264.so.163
> $ /sbin/ldconfig -v 2>/dev/null | grep -A3 hwcap
> /lib/i386-linux-gnu/i686: (hwcap: 0x0002000000000000) (from /etc/ld.so.conf.d/i386-linux-gnu.conf:3)
> /lib/i386-linux-gnu/i686/sse2: (hwcap: 0x0002000000000001) (from /etc/ld.so.conf.d/i386-linux-gnu.conf:3)
> libx264.so.163 -> libx264.so.163
>
> $ cat /etc/ld.so.conf.d/i386-linux-gnu.conf
> # Multiarch support
> /usr/local/lib/i386-linux-gnu
> /lib/i386-linux-gnu
> /usr/lib/i386-linux-gnu
> /usr/local/lib/i686-linux-gnu
> /lib/i686-linux-gnu
> /usr/lib/i686-linux-gnu
>
> $ /lib/ld-linux.so.2 --help
> [...]
> Shared library search path:
> (libraries located via /etc/ld.so.cache)
> /lib/i386-linux-gnu (system search path)
> /usr/lib/i386-linux-gnu (system search path)
> /lib (system search path)
> /usr/lib (system search path)
>
> No subdirectories of glibc-hwcaps directories are searched.
^very neat trick. I was not aware of this command.
> Legacy HWCAP subdirectories under library search path directories:
> i686 (AT_PLATFORM; supported, searched)
> tls (supported, searched)
> sse2 (supported, searched)
>
> So if you have '/usr/lib/i386-linux-gnu' add on your ld.so.cache, the
> <path>/i686/see will be search through legacy hwcap support.
This has been confirmed by Florian since: you'd need glibc 2.37 to
reproduce the behavior I am seeing in Debian/sid.
> >
> >>> Conversely how should I read the following:
> >>>
> >>> % sudo ldconfig -p | grep hwcap
> >>> libfoo.so.160 (libc6,x86-64, hwcap: 0x0004000000000000) =>
> >>> /lib/x86_64-linux-gnu/haswell/libfoo.so.160
> >>> libfoo.so.160 (libc6,x86-64, hwcap: 0x0000000000000004) =>
> >>> /lib/x86_64-linux-gnu/avx512_1/libfoo.so.160
> >>>
> >>> What does "haswell" / "avx512_1" subfolder implies in terms of gcc
> >>> compile options ?
> >>
> >> It's complicated. Nowdays, on x86-64, you can use
> >> glibc-hwcaps/x86-64-v3 and glibc-hwcaps/x86-64-v4, which are designed to
> >> correspond to -march=x86-64-v3 and -march=x86-64-v4, and x86-64-v4 is a
> >> superset of x86-64-v3.
> >
> > Ok, thanks for the update.
> >
> > Could you just review what I see on my Debian/sid/armhf system:
> >
> > % cat /proc/cpuinfo | grep Features | uniq
> > Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4
> > idiva idivt lpae evtstrm
> > % LD_DEBUG=libs LD_LIBRARY_PATH=. /bin/true
> > 2964957: find library=libc.so.6 [0]; searching
> > 2964957: search path=. (LD_LIBRARY_PATH)
> > 2964957: trying file=./libc.so.6
> > 2964957: search cache=/etc/ld.so.cache
> > 2964957: trying file=/lib/arm-linux-gnueabihf/libc.so.6
> > 2964957:
> > 2964957:
> > 2964957: calling init: /lib/ld-linux-armhf.so.3
> > 2964957:
> > 2964957:
> > 2964957: calling init: /lib/arm-linux-gnueabihf/libc.so.6
> > 2964957:
> > 2964957:
> > 2964957: initialize program: /bin/true
> > 2964957:
> > 2964957:
> > 2964957: transferring control: /bin/true
> > 2964957:
> > 2964957:
> > 2964957: calling fini: [0]
> > 2964957:
> > 2964957:
> > 2964957: calling fini: /lib/arm-linux-gnueabihf/libc.so.6 [0]
> > 2964957:
> > 2964957:
> > 2964957: calling fini: /lib/ld-linux-armhf.so.3 [0]
> > 2964957:
> >
> > Based on the above, it seems glibc is setup to never search hwcaps
> > optimized libraries on this system (even if neon/vfpv4 is supported by
> > system).
>
> This is a ubuntu22 armhf chroot on aarch64:
>
> $ /lib/ld-linux-armhf.so.3 --help
> [...]
> Shared library search path:
> (libraries located via /etc/ld.so.cache)
> /lib/arm-linux-gnueabihf (system search path)
> /usr/lib/arm-linux-gnueabihf (system search path)
> /lib (system search path)
> /usr/lib (system search path)
>
> No subdirectories of glibc-hwcaps directories are searched.
>
> Legacy HWCAP subdirectories under library search path directories:
> v8l (AT_PLATFORM; supported, searched)
> tls (supported, searched)
> neon (supported, searched)
> vfp (supported, searched)
>
> So both neon and vfp; I can not say exactly how debian is configured since both
> ubuntu and debian carry out of tree patches; but I would expect them to be
> similar regarding libc.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-09-01 7:18 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-08-31 10:06 glibc-hwcaps for armv7 (neon-vfpv4) Mathieu Malaterre
2023-08-31 11:24 ` Florian Weimer
2023-08-31 12:08 ` Mathieu Malaterre
2023-08-31 15:30 ` Adhemerval Zanella Netto
2023-09-01 7:18 ` Mathieu Malaterre
2023-08-31 17:20 ` Florian Weimer
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