[Bug target/70210] -march=native and -mcpu=native do not detect ARM cortex-a53 in 32 bit mode on Linux

[Bug target/70210] -march=native and -mcpu=native do not detect ARM cortex-a53 in 32 bit mode on Linux

[Viktor.Engelmann at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70210

Viktor Engelmann <Viktor.Engelmann at googlemail dot com> changed:

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                 CC|                            |Viktor.Engelmann@googlemail
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--- Comment #3 from Viktor Engelmann <Viktor.Engelmann at googlemail dot com> ---
I see a (probably related) problem in gcc 9.3 on docker image alpine:latest on
raspberry pi 3. There, Makefiles generated by autoconf pass -mcpu=armv7l.
And you can't just force it to use a different cpu by passing --host= to
./configure in your Dockerfile, because that would break the Dockerfiles'
cross-platform compatibility. This breaks all autoconf projects in docker on
raspberry pi 3.

This shouldn't be that hard IMHO, because -mcpu=armv7l only needs to be
reinterpreted as -mcpu=cortex-a53.

[Bug target/70210] -march=native and -mcpu=native do not detect ARM cortex-a53 in 32 bit mode on Linux

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70210

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |ktkachov at gcc dot gnu.org

--- Comment #4 from ktkachov at gcc dot gnu.org ---
(In reply to Viktor Engelmann from comment #3)
> I see a (probably related) problem in gcc 9.3 on docker image alpine:latest
> on raspberry pi 3. There, Makefiles generated by autoconf pass -mcpu=armv7l.
> And you can't just force it to use a different cpu by passing --host= to
> ./configure in your Dockerfile, because that would break the Dockerfiles'
> cross-platform compatibility. This breaks all autoconf projects in docker on
> raspberry pi 3.
> 
> This shouldn't be that hard IMHO, because -mcpu=armv7l only needs to be
> reinterpreted as -mcpu=cortex-a53.

That's not correct usage though. -mcpu isn't documented to accepted
architecture names (see
https://gcc.gnu.org/onlinedocs/gcc-9.3.0/gcc/ARM-Options.html#ARM-Options for
the accepted list of arguments accepted by mcpu/mtune)

There is the option -march that accepts architecture names, but armv7l isn't a
valid architecture either. I'm not familiar with what Docker does here, but
from the aarch32 GCC backend perspective the architecture for Cortex-A53 is
-march=armv8-a+crc+simd

BTW, I believe the original bug in this report has been fixed for some time.
All currently supported GCC versions (GCC 8.4 onwards) have the right part
number for Cortex-A53

[Bug target/70210] -march=native and -mcpu=native do not detect ARM cortex-a53 in 32 bit mode on Linux

[Viktor.Engelmann at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70210

--- Comment #5 from Viktor Engelmann <Viktor.Engelmann at googlemail dot com> ---
Hmmm the problem isn't related to docker - I get the same problem when I run
gcc on the raspberry directly with -mcpu=armv7l as autoconf does in docker.

When I run gcc manually with -mcpu=cortex-a53, everything is fine.
lscpu says

Architecture:        armv7l
Byte Order:          Little Endian
CPU(s):              4
On-line CPU(s) list: 0-3
Thread(s) per core:  1
Core(s) per socket:  4
Socket(s):           1
Vendor ID:           ARM
Model:               4
Model name:          Cortex-A53
Stepping:            r0p4
CPU max MHz:         1200.0000
CPU min MHz:         600.0000
BogoMIPS:            38.40
Flags:               half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva
idivt vfpd32 lpae evtstrm crc32

and /proc/cpuinfo is basically the same as the one Andrew Roberts had posted.
Maybe it's a problem in autoconf for passing armv7l (the "Architecture:" line)
to -mcpu.

[Bug target/70210] -march=native and -mcpu=native do not detect ARM cortex-a53 in 32 bit mode on Linux

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70210

--- Comment #6 from ktkachov at gcc dot gnu.org ---
(In reply to Viktor Engelmann from comment #5)
> Hmmm the problem isn't related to docker - I get the same problem when I run
> gcc on the raspberry directly with -mcpu=armv7l as autoconf does in docker.
> 

yep, armv7l is not a valid argument to -mcpu by design.

> When I run gcc manually with -mcpu=cortex-a53, everything is fine.
> lscpu says
> 
> Architecture:        armv7l
> Byte Order:          Little Endian
> CPU(s):              4
> On-line CPU(s) list: 0-3
> Thread(s) per core:  1
> Core(s) per socket:  4
> Socket(s):           1
> Vendor ID:           ARM
> Model:               4
> Model name:          Cortex-A53
> Stepping:            r0p4
> CPU max MHz:         1200.0000
> CPU min MHz:         600.0000
> BogoMIPS:            38.40
> Flags:               half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva
> idivt vfpd32 lpae evtstrm crc32
> 
> and /proc/cpuinfo is basically the same as the one Andrew Roberts had posted.
> Maybe it's a problem in autoconf for passing armv7l (the "Architecture:"
> line) to -mcpu.