* __thread_pointer on powerpc
@ 2021-12-15 2:16 Mathieu Desnoyers
2021-12-15 9:01 ` Florian Weimer
0 siblings, 1 reply; 2+ messages in thread
From: Mathieu Desnoyers @ 2021-12-15 2:16 UTC (permalink / raw)
To: Florian Weimer; +Cc: libc-alpha
Hi Florian,
In the recent patchset introducing rseq support in glibc, __thread_pointer
is wired up for powerpc.
Based on my interpretation of
https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/Local-Register-Variables.html
it appears that using "register void *__result asm ("r2")" is not sufficient
to guarantee that the compiler will indeed use this register. It's documented
as being just a hint that the compiler is free to optimize away.
I suspect we may want to add something like:
asm ("" : "=r" (__result));
just after the variable definition, to force the compiler to use this variable
as output to an inline asm.
Thoughts ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: __thread_pointer on powerpc
2021-12-15 2:16 __thread_pointer on powerpc Mathieu Desnoyers
@ 2021-12-15 9:01 ` Florian Weimer
0 siblings, 0 replies; 2+ messages in thread
From: Florian Weimer @ 2021-12-15 9:01 UTC (permalink / raw)
To: Mathieu Desnoyers; +Cc: libc-alpha
* Mathieu Desnoyers:
> Hi Florian,
>
> In the recent patchset introducing rseq support in glibc, __thread_pointer
> is wired up for powerpc.
>
> Based on my interpretation of
>
> https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/Local-Register-Variables.html
>
> it appears that using "register void *__result asm ("r2")" is not sufficient
> to guarantee that the compiler will indeed use this register. It's documented
> as being just a hint that the compiler is free to optimize away.
>
> I suspect we may want to add something like:
>
> asm ("" : "=r" (__result));
>
> just after the variable definition, to force the compiler to use this variable
> as output to an inline asm.
Good point. I think we should use a global register variable instead.
I will try to fix this.
Thanks,
Florian
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