Re: [PATCH 1/3] glibc: Perform rseq registration at C startup and thread creation (v21)

[Mathieu Desnoyers]

----- On Jun 24, 2020, at 3:11 PM, Florian Weimer fweimer@xxxxxxxxxx wrote:

> * Mathieu Desnoyers:
> 
>>> I'm still worried that __rseq_static_assert and __rseq_alignof will show
>>> up in the UAPI with textually different definitions.  (This does not
>>> apply to __rseq_tls_model_ie.)
>>
>> What makes this worry not apply to __rseq_tls_model_ie ?
> 
> It's not needed by the kernel header because it doesn't contain a
> __rseq_abi declaration.
> 
>>> 
>>> Is my worry unfounded?
>>
>> So AFAIU you worry that eventually sys/rseq.h and linux/rseq.h carry different
>> definitions of __rseq_static_assert and __rseq_alignof.
>>
>> Indeed, I did not surround those #define with #ifndef/#endif. Maybe we should ?
>>
>> Just in case the definitions end up being different (worse case scenario), we
>> should expect their behavior to be pretty much equivalent. So going for the
>> following should address your concern I think:
> 
> I think we should keep things simple on the glibc side for now and do
> this changes to the kernel headers first.

Just to be sure I understand what you mean by "keep things simple", do you
recommend removing the following lines completely for now from sys/rseq.h ?

/* Ensure the compiler supports rseq_align.  */
__rseq_static_assert (__rseq_alignof (struct rseq_cs) >= 32, "alignment");
__rseq_static_assert (__rseq_alignof (struct rseq) >= 32, "alignment");

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com