Re: Saving all register of Boehm's Stop-World of hypermodern i686, is it reliable?

["J.C." <jc-nospam at jr-pizarro dot jazztel dot es>]

| J.C. writes:
| > In boehm-gc/pthread_stop_world.c from GCJ-4.3,
| > i don't see any specific information of a modern CPU like AMD Athlon64 
| > AM2 or Intel Pentium-M CoreDuo.
| > 
| > ( to see GC_with_callee_saves_pushed() )
| > 
| > In my opinion, the registers & flags that must to be saved are:
| > 
| > * GP registers & flags (like eax,ebx,..,ebp,esp)
| > * FP registers & flags (like ST(0),..,ST(7))
| > * MMX registers & flags (from MMX)
| > * XMM registers & flags (from SSE, SSE2, SSE3, SSE4, ..)
| > * 3DNow+ registers & flags (very specific from AMD)
| > * future registers & flags of extensions of new microprocessors.
| > 
| > If not all register of a hypermodern i686 is saved then it can 
| > soft-crash the application with a certain probability, and it won't be 
| > good for future searching of unknown bugs.
|
| I think you need to explain to us where you see a vulnerability.  In
| particular, do you expect pointers to be saved in XMM registers?  If
| so, please explain why you expect this.

To imagine a theatre of 2 actors,
the main actor "M" and the Stop-World actor "SW":

M : i'm calling to e.g. app_quick_memcpy that it uses instructions of cache's
prefetching and XMM registers to accelerate the copy, thanks to the e.g.
AMD Athlon Optimization manual. Inside of app_quick_memcpy, it does callings
to several functions.

SW: now, i stop your world and start to collect information of your world,
and i suppose that this traced information will be full.

M: i've unexpected result of app_quick_memcpy, why? why? i don't find the
app_quick_memcpy's BUG. It's harmful for my brain.

SW: I no, no, no, ...

Eleven months after ...

SW: yes, yes, the guilty is me, i'm sorry, i didn't collect the new and
unknown registers of the new microprocessors. The new times are bad for me.

| > Too, if any SIMD register can't be used because of it (the
| > application or library doesn't support), then the GCC compiler
| > doesn't should use SIMD flags, but the GCC can do it.
| > 
| > Then, why are we infra-using the SIMD registers?
|
| What do you mean by "infra-using" ?
|
| Andrew.

Hehehe, i mean "infra-using" as "using less this important thing".

E.g., if the dog has 4 legs because of his existence then,
for optimum performance, the dog uses their 4 legs to walk.

No dog infra-uses his 4th leg unless is ill or joking,
it's mysterious, hahaha.

J.C.