Re: [PATCH] nptl: x86_64: Use same code for CURRENT_STACK_FRAME and stackinfo_get_sp

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

On 30/08/22 15:54, Noah Goldstein wrote:
> On Tue, Aug 30, 2022 at 5:08 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>> It avoids the possible warning of uninitialized 'frame' variable when
>> building with clang:
>>
>>   ../sysdeps/nptl/jmp-unwind.c:27:42: error: variable 'frame' is
>>   uninitialized when used here [-Werror,-Wuninitialized]
>>     __pthread_cleanup_upto (env->__jmpbuf, CURRENT_STACK_FRAME);
>>
>> The resulting code is similar to CURRENT_STACK_FRAME.
>>
>> Checked on x86_64-linux-gnu.
>> ---
>>  sysdeps/x86/nptl/pthreaddef.h | 4 +++-
>>  sysdeps/x86_64/stackinfo.h    | 4 +++-
>>  2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/sysdeps/x86/nptl/pthreaddef.h b/sysdeps/x86/nptl/pthreaddef.h
>> index 63fdbcb27c..7df65931a3 100644
>> --- a/sysdeps/x86/nptl/pthreaddef.h
>> +++ b/sysdeps/x86/nptl/pthreaddef.h
>> @@ -42,7 +42,9 @@
>>  #ifdef __x86_64__
>>  /* The frame pointer is not usable.  */
>>  # define CURRENT_STACK_FRAME \
>> -  ({ register char *frame __asm__("rsp"); frame; })
>> +  ({ register void * p__ __asm__(RSP_REG); \
>> +     asm volatile("" : "=r" (p__)); \
>> +     p__; })
>>  #else
>>  # define CURRENT_STACK_FRAME   __builtin_frame_address (0)
>>  #endif
>> diff --git a/sysdeps/x86_64/stackinfo.h b/sysdeps/x86_64/stackinfo.h
>> index 34c9d0b576..7354632132 100644
>> --- a/sysdeps/x86_64/stackinfo.h
>> +++ b/sysdeps/x86_64/stackinfo.h
>> @@ -40,7 +40,9 @@
>>     for which they need to act as barriers as well, hence the additional
>>     (unnecessary) parameters.  */
>>  #define stackinfo_get_sp() \
>> -  ({ void *p__; asm volatile ("mov %%" RSP_REG ", %0" : "=r" (p__)); p__; })
>> +  ({ register void * p__ __asm__(RSP_REG); \
>> +     asm volatile("" : "=r" (p__)); \
>> +     p__; })
> 
> This change addresses a different issue. Maybe two separate commits?

I am not sure this characterizes as an 'issue', since code does work as is,
the idea is to have the same definition.

> 
> Otherwise LGTM.
>>  #define stackinfo_sub_sp(ptr) \
>>    ({ ptrdiff_t d__;                                            \
>>       asm volatile ("sub %%" RSP_REG " , %0" : "=r" (d__) : "0" (ptr)); \
>> --
>> 2.34.1
>>