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Message-ID: <20150924151536.GJ10551@port70.net>
Date: Thu, 24 Sep 2015 17:15:36 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: Problems? compiling musl toolchain
* Rich Felker <dalias@...c.org> [2015-09-24 11:00:01 -0400]:
> On Thu, Sep 24, 2015 at 04:23:58PM +0200, Ruben Winistörfer wrote:
> > First: Compiling GCC 5.2.0 (and also 4.9.3) with musl 1.1.11
> > toolchain I get a lot of warnings about missing sentinels in
> > function calls. Compiling GCC (same versions) with glibc toolchain
> > there's no such warning at all.
> > Replacing the function call sentinels 'NULL' with '(char *)NULL' in
> > the affected source code of GCC makes the warnings disappear.
>
> This warning is correct; the GCC code is wrong. NULL is not a valid
> way to pass a null pointer to a variadic function, especially not in
> C++ code.
>
> > My question: Does the reason for these warnings have some impact on
> > the health of the toolchain (is there something wrong?) or are they
> > just a byproduct of the correctness and standards-conformance of
> > musl?
>
> musl has arranged things so that this will work ok (and won't blow up)
> at runtime, but what GCC's source is doing formally incorrect and
> should be fixed.
>
the glibc definition, __null (gcc builtin), is not strictly conforming.
in c++11 it is possible to define NULL in such a way that it does
not warn, std::nullptr, but even that's not correct to use in
variadic functions unless the argument type is (void*) or (char*),
so probably the warning is a good thing.
> > Second: Compiling with a musl 1.1.11, GCC 5.2.0 (and 4.9.3),
> > Binutils 2.25.1 toolchain I get the following info (warning) over an
> > over again:
> >
> > ....ld: copy reloc against protected `stdout' is dangerous
> > ....ld: copy reloc against protected `stdin' is dangerous
> > ....ld: copy reloc against protected `stderr' is dangerous
> >
> > Same can be seen in Alpine Linux build logs: e.g. http://build.alpinelinux.org/buildlogs/build-edge-x86_64/main/patchutils/patchutils-0.3.4-r0.log
> >
> > Reason for these "warnings" seems to be a change in the linker from
> > binutils version 2.25 to 2.25.1.
> > Lines 2677 to 2680 in 'binutils-2.25.1/bfd/elflink.c' are new and in
> > my opinion the source of the issued warning.
> > My C knowledge is minimal but as far as I can tell this means that
> > the problem - if there is one at all - was already there before
> > binutils version 2.25.1, the linker just did not print the
> > "warning".
> >
> > I haven't seen this warning before using glibc. So i guess it has to
> > be musl-related.
> >
> > What do you think? Is there a problem or can I ignore these warnings?
>
> You can safely ignore them. I do plan to find a way to make them go
> away in the next release though, since they're confusing and
> concerning to many users.
the warning is disabled on targets that has extern_protected_data
handling since
http://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=889c2a67967f7047c245779a0a0fd8ba8796846e
but binutils has a yearly release cycle so we will have to wait.
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