Re: aarch64 clone() man page omission

[Colin Ian King <colin.king-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>]

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On 09/05/16 22:31, Mike Frysinger wrote:
> On 25 Apr 2016 20:42, Colin Ian King wrote:
>> currently, the aarch64 clone() system call requires the stack to be
>> aligned at a 16 byte boundary, see arch/arm64/kernel/process.c,
>> copy_thread():
>>
>>                 if (stack_start) {
>>                         if (is_compat_thread(task_thread_info(p)))
>>                                 childregs->compat_sp = stack_start;
>>                         /* 16-byte aligned stack mandatory on AArch64 */
>>                         else if (stack_start & 15)
>>                                 return -EINVAL;
>>                         else
>>                                 childregs->sp = stack_start;
>>                 }
>>
>>
>> ..and returns -EINVAL if not aligned correctly.  This should be added to
>> the manual page clone(2) as it took me a while to figure out why clone()
>> was failing with -EINVAL for aarch64 but not on x86.
> 
> seems weird for the kernel to be enforcing this.  is it just because of
> the stated ABI ?  or is there some weird requirement in the kernel itself
> that requires this ?  it's not like other arches have this check, and
> there are def ABI requirements about stack alignments in C.
> -mike
> 
The article here indicates it is an aarch64 convention:

https://community.arm.com/groups/processors/blog/2015/11/19/using-the-stack-in-aarch32-and-aarch64





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