GNU bug report logs - #29600
Emacs port to gcc -fcheck-pointer-bounds

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Emacs bug reports and feature requests <bug-gnu-emacs <at> gnu.org>
Subject: Emacs port to gcc -fcheck-pointer-bounds
Date: Wed, 6 Dec 2017 23:18:35 -0800

[Message part 1 (text/plain, inline)]

Attached is a series of three patches to port Emacs to 'gcc 
-fcheck-pointer-bounds'. This feature enables hardware bounds checking for some 
internal pointers of the Emacs interpreter, and I've used it to find a bug in 
Emacs itself. It's intended primarily for debugging Emacs internals, and is off 
by default. I would like to install these patches soon unless some problems turn 
up, and am submitting this as a bug report in case others who care about Emacs 
low-level internals would like to review the patches.

The first patch changes the basic Emacs internal type from an integer to a 
pointer of the same width. Although this doesn't significantly affect ordinary 
builds it's essential for -fcheck-pointer-type, where the C compiler must be 
told the location of every pointer (including tagged pointers) for the checking 
to work well. (No doubt I'm partial, but I think this patch also cleans up Emacs 
internals a bit even for typical platforms.) The patch should not change the 
behavior of the Emacs interpreter; it's mostly just treating some intptr_t 
values as pointer values instead.

The second patch builds on the first to fix Emacs so that it doesn't crash when 
-fcheck-pointer-bounds is used.

The third patch enables more pointer bounds checking. Not every pointer access 
is checked, just the ones for which -fcheck-pointer-bounds is easy. Although 
this doesn't catch every pointer-bounds error, it does catch some of them. 
Perhaps more checking could be added later.

[0001-Reimplement-Lisp_Object-as-pointer-to-incomplete.patch (text/x-patch, attachment)]

[0002-Port-to-gcc-fcheck-pointer-bounds.patch (text/x-patch, attachment)]

[0003-Narrow-pointer-bounds-when-appropriate.patch (text/x-patch, attachment)]

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