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Date: Tue, 30 Aug 2016 16:54:28 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: assert_fail without Noreturn
On Mon, Aug 29, 2016 at 08:05:00PM -0400, Assaf Gordon wrote:
> Hello,
>
> It seems "assert_fail()" does not have a "noreturn" attribute - it was removed in this commit:
>
> commit 2c1f8fd5da3306fd7c8a2267467e44eb61f12dd4
> Author: rofl0r <retnyg@....net>
> Date: Tue Jan 1 07:59:11 2013 +0100
>
> __assert_fail(): remove _Noreturn, to get proper stack traces
>
> for _Noreturn functions, gcc generates code that trashes the
> stack frame, and so it makes it impossible to inspect the causes
> of an assert error in gdb.
>
> abort() is not affected (i have not yet investigated why).
>
>
> However, in recent GCC versions (at least 5.2.0) this causes a compiler warning (or error with -Werror).
>
> A contrived example:
>
> $ cat 2.c
>
> #include <assert.h>
> #include <stdio.h>
>
> FILE* foo (int i)
> {
> FILE *f;
> if (i>0)
> f = fopen("foo.bar","r");
> else
> assert(!"error");
> return f;
> }
>
> $ musl-gcc -O2 -Wall -Wextra -c 2.c
> 2.c: In function ‘foo’:
> 2.c:12:11: error: ‘f’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> return f;
> ^
> cc1: some warnings being treated as errors
>
> Using 'gcc' instead of 'musl-gcc' shows no warnings.
>
> The compiler is:
>
> $ musl-gcc -v
> Using built-in specs.
> Reading specs from /usr/local/musl/lib/musl-gcc.specs
> rename spec cpp_options to old_cpp_options
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/5.2.0/lto-wrapper
> Target: x86_64-unknown-linux-gnu
> Configured with: ../gcc-5.2.0/configure --enable-languages=c,c++
> Thread model: posix
> gcc version 5.2.0 (GCC)
>
> Using musk-libc version 1.1.15 from tarball.
>
> Perhaps putting "_Noreturn" in "assert_fail" can be reconsidered ?
> Or perhaps there's another way to avoid this warning ?
I'm reverting commit 2c1f8fd5da3306fd7c8a2267467e44eb61f12dd4 based on
discussion with the patch contributor and testing. Further details
will be in the commit message. Thanks!
Rich
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