Where/how is T_STKFLT handled? [OpenBSD/TECH]

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02-22-2008, 11:27 AM

Jason W. Kim

Posts: n/a

Where/how is T_STKFLT handled? [OpenBSD/TECH]

Hi all,

yet another question from yours truly.

I've been trying to figure out how OpenBSD handles stack growth for user
processes.

Near arch/i386/i386/trap.c:368
case T_SEGNPFLT|T_USER:
case T_STKFLT|T_USER:
sv.sival_int = frame.tf_eip;
KERNEL_PROC_LOCK(p);
trapsignal(p, SIGSEGV, vftype, SEGV_MAPERR, sv);
KERNEL_PROC_UNLOCK(p);
goto out;

Ok, so trapsignal() gets called to handle the error.
But near sys/kern/kern_sig.c:779

(*p->p_emul->e_sendsig)(ps->ps_sigact[signum], signum,

Where is the p_emul->e_sendsig set? What is it set to?

I did a recursive grep, but no luck - is it set in an assembly file
somewhere disguised as a different offset name or something?
Or is this only used when running execs from different OS's?

Without any additional detail, I'll make a guess that somewhere,
somehow, a uvm_map() gets called which will add new stack mappings to
the offending process - is this accurate? if not, can anyone point me to
the right place to look?

Thanks,
-Jason Kim

« Re: strtonum(3) in FreeBSD? | Re: Where/how is T_STKFLT handled? [OpenBSD/TECH] »

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Where/how is T_STKFLT handled? [OpenBSD/TECH]