On Thu, 26 Oct 2023 15:20:22 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> Anyway, I changed the code to use:
> 
> static inline unsigned clrbit(volatile unsigned *ptr)
> {
> 	unsigned ret;
> 
> 	asm volatile("andb %b1,%0"
> 		     : "+m" (*(volatile char *)ptr)
> 		     : "iq" (0x2)
> 		     : "memory");
> 
> 	ret = *ptr;
> 	*ptr = 0;
> 
> 	return ret;
> }

Mathieu also told me that glibc's rseq has some extra padding at the end,
that happens to be big enough to hold this feature. That means you can run
the code without adding:

  GLIBC_TUNABLES=glibc.pthread.rseq=0

Attached is the updated test program.

-- Steve