Re: [AD] x color conversion again (w/ responsiveness patch)

[Chris <kcat@xxxxxxxxxx>]

Elias Pschernig wrote:
> Well. My theory is: *Something* in the asm-color-converters doesn't get
> preserved over an interrupting signal. I.e., the signal enters somewhere
> inside the asm, and therefore, a register or flag is modifed. Or, since
> we do no X11 locking in the signals version, the memory the asm
> converters are accessing is volatile and is invalidated when a signal
> occurs?

Hmm.. googling for 'how linux signals work', I ran across this:
http://www.linuxjournal.com/article.php?sid=3985

This quote here seems to indicate that the signal is indeed being called 
from a different context, if not a different thread:

"The occurrence of a signal may be synchronous or asynchronous to the 
process or thread, depending on the source of the signal and the 
underlying reason or cause. Synchronous signals occur as a direct result 
of the executing instruction stream, where an unrecoverable error (such 
as an illegal instruction or illegal address reference) requires an 
immediate termination of the process. Such signals are directed to the 
thread which caused the error with its execution stream. [...]

Asynchronous signals are external to (and in some cases, unrelated to) 
the current execution context. One obvious example would be the sending 
of a signal to a process from another process or thread via a kill(2), 
_lwp_kill(2) or sigsend(2) system call, or a thr_kill(3T), 
pthread_kill(3T) or sigqueue(3R) library invocation. Asynchronous 
signals are also aptly referred to as interrupts."

If SIGALRM is also asynchronous, then that means we'd definately have 
problems calling X routines from it. Also, the rest of the document 
leads me to believe that signals do indeed have the same stack trappings 
as a hardware interrupt.. ie. no FPU stack. I tried asking Bob in 
#allegro if MMX would have the same problems, but he's not around. It 
does make sense since I compiled Allegro with -mmmx which enables MMX 
usage in the produced asm, which includes the signal handlers.

I'll try building the signal version of 4.1.14 and let you guys know how 
it goes.

- Kitty Cat