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From: "stsp at users dot sourceforge.net"
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To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/30007] rfe: dlopen to specified address
Date: Sun, 19 Mar 2023 09:47:02 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D30007

--- Comment #18 from Stas Sergeev <stsp at users dot sourceforge.net> ---
(In reply to Stas Sergeev from comment #16)
> I am not even sure why the first segment
> should be at the beginning, does it
> always have the vaddr=3D=3D0? But so do the
> comments in the present code suggest.

Actually it doesn't suggest that and
all segments are over-mapped over the
initial mapping. I'll need to re-check
my changes to _dl_map_segment() to see
if I got the things right.
But given that all segments are over-mapped,
certainly there is no reason to trap
the first mmap call.
Of course now I have some very bad feeling
that your next proposal will be "trap
all mmaps, not just the first one"...
Well, before you do that, consider the
following:
1. Some mappings are converted from
   file-based to anonymous via mprotect+memset.
2. _dl_map_segment() handles the "large
   alignment" case with 2 mmaps. The first
   large one is done only for alignment, and
   should I share with VM also that?
3. Do you really think that trapping all
   mmaps and trying to hack around the
   aforementioned problems, is a good idea?

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