Re: [PATCH] support: arm: Add libc_do_syscall function to libsupport routines

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 16/03/2021 02:10, Florian Weimer wrote:
> * Lukasz Majewski:
> 
>> Hi Florian,
>>
>>> * Lukasz Majewski:
>>>
>>>> It fixes the following error on ARM 32 bit port:
>>>>
>>>> y2038-glibc/support/support_path_support_time64.c:34: undefined
>>>> reference to `__libc_do_syscall'
>>>> collect2: error: ld returned 1 exit status  
>>>
>>> Should libsupport use syscall for direct system calls?
>>
>> I'm not sure what is the correct approach here.
>>
>> In my case - armv7, 32 bit - in support/support_path_support_time64.c
>> the utimensat_time64 syscall is called, which is wrapped to
>> INLINE_SYSCALL_CALL(), which calls __libc_do_syscall ASM ARM function.
>>
>> This function is only defined for i386 and 32 bit ARM (in e.g.
>> sysdeps/unix/sysv/linux/{arm|i386}/libc-do-syscall.S)
> 
> Yes, and using the syscall function would avoid this issue.
> 
> So the question is, why INLINE_SYSCALL_CALL?

The __libc_do_syscall is in fact only used thumb mode used as default,
and the direct syscall is used because there is no direct support
for using 64 bit types on ABI with default 32 bit time.  We might 
eventually remove the INLINE_SYSCALL_CALL once 64 bit time support is 
implemented (so we build the file with _TIME_SIZE=64).

The patch itself looks ok.