RE: [Linux-ia64] determining read or write on a page fault

["Boehm, Hans" <hans_boehm@hp.com>]

The code for retrieving the address is identical to what I use in our
garbage collector.

According to David Mosberger, there is currently no way to distinguish
between a read and a write fault.  This is nontrivial to change because a
SIGSEGV is sometimes generated in cases in which it is not clear which would
be appropriate.

I suspect the best solution is to decode the faulting instruction
sufficiently to distinguish loads from stores.  I haven't written that code
for Itanium, but my guess is that it's actually not that hard.  David points
out that this will fail if the code is not readable, e.g. if the fault
occurred in the signal trampoline.  (In any case, you need to deal with page
faults in system calls separately, e.g. by avoiding them.)

Hans

> -----Original Message-----
> From: Hoeflinger, Jay P [mailto:jay.p.hoeflinger@intel.com]
> Sent: Thursday, February 21, 2002 1:10 PM
> To: 'linux-ia64@linuxia64.org'
> Subject: [Linux-ia64] determining read or write on a page fault
> 
> 
> We are writing software that handles page faults on an 
> Itanium system, and
> so have registered a SIGSEGV
> handler.  We think we know how to determine the address being 
> referenced,
> but don't know how to determine
> whether the access was a read or a write.
> 
> We believe that the handler entry point should be:
> 
> void
> segv_handler(
>         int                  sig,
>        siginfo_t *sip, 
>         struct sigcontext *scp)
> 
> and the address of the access therefore should be:
> 
> ((caddr_t)sip->si_addr)
> 
> but how do we determine READ vs WRITE?
> 
> In IA-32 linux, we could check the PF_ERR bit.  Is there an 
> equivalent for
> IA-64?
> 
> Thanks
> 
> Naveen Neelakantam and Jay Hoeflinger
> 
> 
> Jay Hoeflinger, jay.p.hoeflinger@intel.com
> KAI Software, A Division of Intel Americas, Inc., http://www.kai.com
> Phone 217/356-2288, Direct 217/356-5052 x 140, Fax 217/356-5199
> 
> 
> 
> _______________________________________________
> Linux-IA64 mailing list
> Linux-IA64@linuxia64.org
> http://lists.linuxia64.org/lists/listinfo/linux-ia64
>