[PATCH v15 6/8] nptl: Move the rseq area to the 'extra TLS' block

[Michael Jeanson]

On 2025-01-08 04:40, Florian Weimer wrote:
> * Michael Jeanson:
> 
>> +#if TLS_TCB_AT_TP
>> +  /* The rseq area block should come before the thread pointer and be at least
>> +     32 bytes. */
>> +  TEST_VERIFY (__rseq_offset <= -RSEQ_AREA_SIZE_INITIAL);
>> +#elif TLS_DTV_AT_TP
>> +  /* The rseq area block should come after the thread pointer. */
>> +  TEST_VERIFY (__rseq_offset + TLS_TP_OFFSET >= 0);
> 
> I think the TLS_TP_OFFSET is redudant here.  It's supposed have already
> been folded into __rseq_offset.  It certainly was before because a
> pointer difference was used to compute it.

I should have updated the comment here, I'm testing that the rseq area
comes after the TCB on TLS_DTV_AT_TP architectures, my first iteration
looked like this:

  TEST_VERIFY (__rseq_offset >= -TLS_TP_OFFSET);

but I felt it was not very readable.

Would this be better?

 +  /* The rseq area block should come after the TCB, add the TLS block
 +     offset to the rseq offset to get a value relative to the TCB and
 +     test that it's positive.  */
 +  TEST_VERIFY (__rseq_offset + TLS_TP_OFFSET >= 0);

Thanks,
Michael