Re: [FFmpeg-devel] aarch64: Implement support for elf_aux_info(3) on FreeBSD and OpenBSD

["Martin Storsjö" <martin@martin.st>]

On Sun, 28 Jul 2024, Rémi Denis-Courmont wrote:

> Le 28 juillet 2024 07:37:51 GMT+03:00, Brad Smith <brad-at-comstyle.com@ffmpeg.org> a écrit :
>> On 2024-07-26 7:56 a.m., Rémi Denis-Courmont wrote:
>>> 
>>> Le 26 juillet 2024 13:58:34 GMT+03:00, Brad Smith <brad-at-comstyle.com@ffmpeg.org> a écrit :
>>>> aarch64: Implement support for elf_aux_info(3) on FreeBSD and OpenBSD
>>>> 
>>>> FreeBSD 12.0+, OpenBSD -current and what will be OpenBSD 7.6 support
>>>> elf_aux_info(3).
>>>> 
>>>> Signed-off-by: Brad Smith <brad@comstyle.com>
>>>> ---
>>>> configure               |  2 ++
>>>> libavutil/aarch64/cpu.c | 23 ++++++++++++++++++++++-
>>>> 2 files changed, 24 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/configure b/configure
>>>> index f6f5c29fea..e80b549582 100755
>>>> --- a/configure
>>>> +++ b/configure
>>>> @@ -2366,6 +2366,7 @@ SYSTEM_FUNCS="
>>>>      clock_gettime
>>>>      closesocket
>>>>      CommandLineToArgvW
>>>> +    elf_aux_info
>>>>      fcntl
>>>>      getaddrinfo
>>>>      getauxval
>>>> @@ -6565,6 +6566,7 @@ check_func_headers mach/mach_time.h mach_absolute_time
>>>> check_func_headers stdlib.h getenv
>>>> check_func_headers sys/stat.h lstat
>>>> check_func_headers sys/auxv.h getauxval
>>>> +check_func_headers sys/auxv.h elf_aux_info
>>>> check_func_headers sys/sysctl.h sysctlbyname
>>>> 
>>>> check_func_headers windows.h GetModuleHandle
>>>> diff --git a/libavutil/aarch64/cpu.c b/libavutil/aarch64/cpu.c
>>>> index cfa9306663..05272b4db4 100644
>>>> --- a/libavutil/aarch64/cpu.c
>>>> +++ b/libavutil/aarch64/cpu.c
>>>> @@ -42,6 +42,27 @@ static int detect_flags(void)
>>>>      return flags;
>>>> }
>>>> 
>>>> +#elif (defined(__FreeBSD__) || defined(__OpenBSD__)) && HAVE_ELF_AUX_INFO
>>>> +#include <stdint.h>
>>>> +#include <sys/auxv.h>
>>>> +
>>>> +static int detect_flags(void)
>>>> +{
>>>> +    int flags = 0;
>>>> +
>>>> +    unsigned long hwcap = 0;
>>>> +    elf_aux_info(AT_HWCAP, &hwcap, sizeof hwcap);
>>>> +    unsigned long hwcap2 = 0;
>>>> +    elf_aux_info(AT_HWCAP2, &hwcap2, sizeof hwcap2);
>>>> +
>>>> +    if (hwcap & HWCAP_ASIMDDP)
>>>> +        flags |= AV_CPU_FLAG_DOTPROD;
>>>> +    if (hwcap2 & HWCAP2_I8MM)
>>>> +        flags |= AV_CPU_FLAG_I8MM;
>>>> +
>>>> +    return flags;
>>>> +}
>>>> +
>>> Can't getauxval() be implemented with elf_aux_info(), or vice versa? It seems that otherwise the code should be identical to that from Linux.
>>
>> QEMU has qemu_getauxval() for example as a wrapper. I will be using this elsewhere for arm, ppc and riscv.
>>
>> I could split this up, but I am not sure where to place such a function.
>
> I don't personally have a strong opinion on the details, I just don't fancy unnecessary duplication.

I don't have a very strong opinion on it either, but if it's reasonable to 
make this a static inline function in a header, it could e.g. be in the 
compat directory, or just as a private header in libavutil.

// Martin
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