GNU bug report logs - #49261
28.0.50; File Locking Breaks Presumptuous Toolchains

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Package: emacs;

Reported by: Mallchad Skeghyeph <ncaprisunfan <at> gmail.com>

Date: Mon, 28 Jun 2021 18:28:02 UTC

Severity: normal

Found in version 28.0.50

Fixed in version 28.1

Done: Lars Ingebrigtsen <larsi <at> gnus.org>

Bug is archived. No further changes may be made.

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Message #230 received at 49261 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: larsi <at> gnus.org, 49261 <at> debbugs.gnu.org
Subject: Re: bug#49261: Segfault during loadup
Date: Mon, 12 Jul 2021 00:16:07 -0700

[Message part 1 (text/plain, inline)]
On 7/11/21 8:25 AM, Eli Zaretskii wrote:

>>    lisp.h:251:18: warning: unsigned conversion from 'long long int' to 'uintptr_t' {aka 'unsigned int'} changes value from '2305843009213693951' to '4294967295' [-Woverflow]
>>      251 | # define VALMASK (USE_LSB_TAG ? - (1 << GCTYPEBITS) : VAL_MAX)
>> 	|                  ^
>>    alloc.c:4767:24: note: in expansion of macro 'VALMASK'
>>     4767 |       uintptr_t mask = VALMASK;
>> 	|                        ^~~~~~~
> I tried to fix this on master, please take a look.

Yes that GCC warning was bogus, and your pacification of GCC is valid 
now that we no longer tag the MSB of pointers. Still, there should be a 
simpler way to pacify GCC so I installed a further fix that I hope does 
that (see first attached patch). This fix simply uses a cast (uintptr_t) 
VALMASK to pacify GCC; if GCC issues a bogus warning even for that cast, 
we could substitute (uintptr_t) (VALMASK & UINTPTR_MAX) though this is 
starting to get a little ridiculous.

The version of GCC that I tried (11.1.1 20210531 (Red Hat 11.1.1-3)) 
don't warn about the original code, so perhaps the bogus warning that 
you saw is a GCC bug that's been fixed in later GCC versions. However, 
GCC 11.1.1 does warn about some other stuff so I installed the remaining 
patches to pacify it. Some of these patches fix real (albeit unlikely) 
bugs in Emacs. Some work around what are evidently flaws in GCC 11.1.1. 
Oh well.

[0001-Pacify-gcc-Woverflow-more-nicely.patch (text/x-patch, attachment)]
[0002-Pacify-gcc-11.1.1-Wanalyzer-null-argument.patch (text/x-patch, attachment)]
[0003-Pacify-gcc-11.1.1-Wanalyzer-possible-null-dereferenc.patch (text/x-patch, attachment)]
[0004-Pacify-gcc-11.1.1-Wclobbered.patch (text/x-patch, attachment)]
[0005-Port-test-module-to-glibc-2.33.patch (text/x-patch, attachment)]
This bug report was last modified 3 years and 306 days ago.

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