linux-kernel - Re: linux-next 20220125 - build failure in objtool with gcc 12

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Date:   Thu, 27 Jan 2022 09:34:34 -0600
From:   Justin Forbes <jmforbes@...uxtx.org>
To:     Valdis Klētnieks <valdis.kletnieks@...edu>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux-next 20220125 - build failure in objtool with gcc 12

On Wed, Jan 26, 2022 at 4:57 PM Valdis Klētnieks
<valdis.kletnieks@...edu> wrote:
>
> Fedora Rawhide shipped gcc12, which apparently includes a new warning that
> causes a build failure.  Apparently, it's unable to figure out that 'ptr' remains
> valid on failed realloc(), and we only call realloc() again on failures...

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104069 explains (toward
the end) why gcc is leaving it to be fixed in the kernel.


>   CC      /usr/src/linux-next/tools/objtool/exec-cmd.o
>   CC      /usr/src/linux-next/tools/objtool/help.o
> In file included from help.c:12:
> In function 'xrealloc',
>     inlined from 'add_cmdname' at help.c:24:2:
> subcmd-util.h:56:23: error: pointer may be used after 'realloc' [-Werror=use-after-free]
>    56 |                 ret = realloc(ptr, size);
>       |                       ^~~~~~~~~~~~~~~~~~
> subcmd-util.h:52:21: note: call to 'realloc' here
>    52 |         void *ret = realloc(ptr, size);
>       |                     ^~~~~~~~~~~~~~~~~~
> subcmd-util.h:58:31: error: pointer may be used after 'realloc' [-Werror=use-after-free]
>    58 |                         ret = realloc(ptr, 1);
>       |                               ^~~~~~~~~~~~~~~
> subcmd-util.h:52:21: note: call to 'realloc' here
>    52 |         void *ret = realloc(ptr, size);
>       |                     ^~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> make[4]: *** [/usr/src/linux-next/tools/build/Makefile.build:97: /usr/src/linux-next/tools/objtool/help.o] Error 1
> make[3]: *** [Makefile:59: /usr/src/linux-next/tools/objtool/libsubcmd-in.o] Error 2
> make[2]: *** [Makefile:63: /usr/src/linux-next/tools/objtool/libsubcmd.a] Error 2
> make[1]: *** [Makefile:69: objtool] Error 2
> make: *** [Makefile:1405: tools/objtool] Error 2