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Date: Fri, 10 Feb 2006 19:06:00 -0000
From: Daniel Jacobowitz <drow@false.org>
To: Andreas Schwab <schwab@suse.de>
Cc: David Lecomber <david@lecomber.net>, gdb <gdb@sources.redhat.com>
Subject: Re: Whacky ia64: linux_proc_xfer_partial and lseek vs pread64
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On Fri, Feb 10, 2006 at 08:00:23PM +0100, Andreas Schwab wrote:
> Daniel Jacobowitz <drow@false.org> writes:
> 
> > On Fri, Feb 10, 2006 at 07:04:51PM +0100, Andreas Schwab wrote:
> >> pread and lseek with SEEK_SET do not allow negative offsets.  lseek on
> >> /proc/$$/mem is a special exception.
> >
> > Uh-oh.  Should pread have the same exception, or must we fall back to
> > lseek?
> 
> pread fails upfront with offset < 0, whereas lseek lets the filesystem
> llseek function decide.  But a fallback wouldn't help here anyway, because
> you can't read the vdso memory with read, only with ptrace.

Fascinating.  That definitely seems like a kernel bug to me; why not?

I see some magic bits in the kernel ptrace support to read backing
stores, which are obviously going to get fouled up by pread support.
But I don't see anything that would affect the vDSO.

-- 
Daniel Jacobowitz
CodeSourcery