stack_used() not accurate?

[Frank Ch. Eigler]

Jim Keniston <jkenisto@us.ibm.com> writes:

> That's certainly a reasonable interpretation of what REG_SP is supposed
> to mean.

This makes sense to me.

> Another reasonable interpretation is "the stack-pointer member
> of pt_regs."  

If they knew the member per se, they could just use it.

> The latter interpretation actually has more subscribers in the
> SystemTap source, as indicated by the use of &REG_SP(regs) in
> stack-*.c.

I don't understand these.  Do ia64, ppc64, and s390 have the same
peculiarity as x86 in the pt_regs->*sp not actually containing the
trap-time stack pointer value?  Or is it just a coincidence that it
works, as in having the pt_regs structure itself be physically
allocated/placed on the probe context stack, so that the address
of any field will point somewhere into the stack?

- FChE