Date: Mon, 6 Dec 1999 16:40:49 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: freebsd-hackers@freebsd.org Subject: Is part of user stack always mapped? Message-ID: <14412.10798.476867.196687@grasshopper.cs.duke.edu>
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I've been getting the osf1ulator (alpha/osf1 abi ported from NetBSD
over a year ago) on its feet again after this fall's signal changes.
When looking closely at the emulators which are currently in the tree,
I notice that they are they directly dereferencing memory which was
allocated on the user's stack via stackgap_alloc() from within the
kernel.
stackgap_init()
{
#define szsigcode (*(curproc->p_sysent->sv_szsigcode))
return (caddr_t)(((caddr_t)PS_STRINGS) - szsigcode - SPARE_USRSPACE);
}
static __inline void *
stackgap_alloc(sgp, sz)
caddr_t *sgp;
size_t sz;
{
void *p = (void *) *sgp;
*sgp += ALIGN(sz);
return p;
}
<...>
sigset_t *set;
caddr_t sg;
sg = stackgap_init();
set = stackgap_alloc(&sg, sizeof(sigset_t));
*set = p->p_sigmask;
<..>
I was under the impression that this was a no-no & one should use
copyin/copout & friends to access memory on users's stacks. Although
this appears to work on the i386, if I try this on the alpha I take a
fatal trap when accessing *set.
So -- how does this work on the i386? Is the user's stack always
mappeped into the kernel's address space? Should it also work on the
alpha?
Apologies for wasting your time if I'm missing something obvious,
------------------------------------------------------------------------------
Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin
Duke University Email: gallatin@cs.duke.edu
Department of Computer Science Phone: (919) 660-6590
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