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Date: Wed, 18 Dec 2024 19:35:43 +0100
To: cygwin AT cygwin DOT com
Subject: Re: Atomic mmap replacement
Message-ID: <Z2MV__BG-IdmtGvc@calimero.vinschen.de>
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Cc: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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On Dec 18 10:45, Ken Brown via Cygwin wrote:
> On 12/18/2024 9:28 AM, Corinna Vinschen via Cygwin wrote:
> > Hi Ken,
> > 
> > On Dec 17 15:23, Ken Brown via Cygwin wrote:
> > > Hi Corinna,
> > > 
> > > On 12/17/2024 11:38 AM, Corinna Vinschen via Cygwin wrote:
> > > > Ideally a separate patch.  If you see a chance to send it to cygwin-patches
> > > > this week, we can even merge it into 3.5.5, which I'm planning to release
> > > > end of this week (after that --> vacation :)))
> > > That should be no problem.  By the way, I think I found a second bug.
> > > Shouldn't mmap:649 be
> > > 
> > > (*)  if (u_addr > (caddr_t) addr || u_len < len
> > > 
> > > instead of
> > > 
> > > (**)  if (u_addr > (caddr_t) addr || u_addr + len < (caddr_t) addr + len
> > > 
> > > ?
> > > 
> > > If the first condition in (**) fails, then u_addr == addr, so the second
> > > condition is automatically false.  But what we want to be testing at this
> > > point is whether the matched region is big enough, as in (*).  Or am I
> > > confused?
> > 
> > u_addr could be < addr.  We have two areas, the free area in u_addr and
> > u_len, and the requested area in addr and len.
> > 
> > So we have to check that addr is >= u_addr and addr + len is <= u_len:
> > 
> >    |----------------------------------------------------|
> >   u_addr                                           u_addr + u_len
> > 
> >             |--------------------|
> >            addr             addr + len
> > 
> > Make sense?
> No, I'm still confused.  I thought that the interval determined by u_addr
> and u_len was the intersection of the requested interval and the whole
> interval of the mmap_record; this implies u_addr >= addr.  Back in the
> definition of mmap_record::match, we set low = max (addr, get_address ()),
> and then on success we set m_addr = low.  Doesn't that imply m_addr >= addr?
> Sorry if I'm just being dense.

Apologies, I didn't check mmap_record::match().  You're right of course.
So, yeah, just go ahead.


Thanks,
Corinna

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