On Thursday 19 January 2006 01:08, Jeff Dike wrote:
> On Wed, Jan 18, 2006 at 05:42:56PM +0100, Blaisorblade wrote:
> > What about this? Inserting an asm volatile clobbering all unsaved
> > registers (what I thought for long time)?
> The gcc doc is somewhat confusing. I read your description as saying
> that locals may be totally smashed to random numbers (and the first
> sentence in the gcc description implies that as well).
I agree with that.
> However, the
> example they give is a pathological case where a local may have one of
> two (well-defined) values, and it's not defined which of those two
> well-defined values it will end up with.
It's confusing. Standard conformance page says that:
* On some rare x86 targets, `setjmp' doesn't save the registers
in all circumstances. In those cases, GCC doesn't allocate
any variables in registers unless they are marked `register'.
But we know it's totally wrong.
The example under "Incompatibilities of GCC" is what you say. However, it's
just because it's a little example. If the var is placed in a register, and
after a lot you longjmp there, that register is totally smashed.
> > Or taking the libc implementation and suiting
> > it for our use, solving the above problem?
> Yuck. But how big is it?
Don't know... I suggested this mainly for the volatile vars problem, more than
for the "access stack" problem.
> Another possibility is to do the magic wakeup thing we do with
> mconsole stack, and have it tell us what it registers are. Not sure
> if that's any better.
You mean mconsole_kern.c:do_stack()? Hmm, ugly too, but more reliable, and not
relying on glibc at least.
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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