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Subject: Re: warning: unsequenced modification and access to 'sa_avail'
Date: Sat, 27 Mar 2021 18:17:04 +0100
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Archived-At:
> Am 27.03.2021 um 18:10 schrieb Jeffrey Walton :
>=20
> On Sat, Mar 27, 2021 at 1:01 PM Philipp wrote:
>>=20
>>> Am 27.03.2021 um 17:05 schrieb Jeffrey Walton :
>>>=20
>>> I'm building Emacs 27.2 on the Apple M1 machine. I think the =
compiler
>>> is complaining about undefined behavior:
>>>=20
>>> sa_avail -=3D (size), alloca (size)
>>>=20
>>> I think it is equivalent to something like this:
>>>=20
>>> data[i] =3D data[i++];
>>>=20
>>> /usr/bin/clang -c -I/usr/local/include -DNDEBUG -Demacs -I. -I.
>>> -I../lib -I../lib -I/usr/local/include/libxml2
>>> -I/usr/local/include -MMD -MF deps/doc.d -MP
>>> -I/usr/local/include -I/usr/local/include/p11-kit-1 -Wno-switch
>>> -Wno-pointer-sign -Wno-string-plus-int -Wno-unknown-attributes
>>> -Wno-initializer-overrides -Wno-tautological-compare
>>> -Wno-tautological-constant-out-of-range-compare -g2 -O2 -fno-common
>>> -arch arm64 -fPIC -pthread doc.c
>>> /usr/bin/clang -c -I/usr/local/include -DNDEBUG -Demacs -I. -I.
>>> -I../lib -I../lib -I/usr/local/include/libxml2
>>> -I/usr/local/include -MMD -MF deps/editfns.d -MP
>>> -I/usr/local/include -I/usr/local/include/p11-kit-1 -Wno-switch
>>> -Wno-pointer-sign -Wno-string-plus-int -Wno-unknown-attributes
>>> -Wno-initializer-overrides -Wno-tautological-compare
>>> -Wno-tautological-constant-out-of-range-compare -g2 -O2 -fno-common
>>> -arch arm64 -fPIC -pthread editfns.c
>>> editfns.c:2063:18: warning: unsequenced modification and access to =
'sa_avail'
>>> [-Wunsequenced]
>>> .deletions =3D SAFE_ALLOCA (del_bytes),
>>> ^
>>> ./lisp.h:4817:9: note: expanded from macro 'SAFE_ALLOCA'
>>> ? AVAIL_ALLOCA (size) =
\
>>> ^
>>> ./lisp.h:4812:38: note: expanded from macro 'AVAIL_ALLOCA'
>>> #define AVAIL_ALLOCA(size) (sa_avail -=3D (size), alloca (size))
>>> ^
>>>=20
>>=20
>> This has already been fixed by commit =
6a4ed891d84b1ca1e4d68a6de9dd374f1fadd971, which hasn't made it into the =
release though.
>=20
> Thanks Philipp.
>=20
> Forgive my ignorance... Where is that commit? I can't seem to find it
> at https://git.savannah.gnu.org/cgit/emacs.git/log/?h=3Demacs-27.
> Searching the logs for your name, and searching for
> 6a4ed891d84b1ca1e4d68a6de9dd374f1fadd971 (and 6a4ed891d84b) returns 0
> hits.
>=20
Try 'git show 6a4ed891d84b1ca1e4d68a6de9dd374f1fadd971'. Right now it's =
the ninth-most recent commit on the emacs-27 branch.