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Date: Wed, 23 Apr 2014 04:47:55 -0400
From: "writeonce@...ipix.org" <writeonce@...ipix.org>
To: musl@...ts.openwall.com
Subject: Re: musl-llvm and crtbegin/crtend
On 04/22/2014 06:38 PM, Rich Felker wrote:
> On Tue, Apr 22, 2014 at 05:53:14PM -0400, writeonce@...ipix.org wrote:
>> Greetings,
>>
>> First issue, and probably an easy fix, is the link to crtbegin.S and
>> crtend.S on the musl wiki page entitled BuildingLLVM. The current
>> links are broken, and should (probably) point to
>> http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/csu/ (the actual files
>> are under arch/{$ARCH}
>>
>> More importantly, though: from very recent communication on the
>> clang developer list, it is my understanding that the NetBSD
>> crtbegin/crtend are the _de facto_ standard for self-hosting clang
>> toolchains. If that is the case, does anyone know of a special
>> license exception pertaining to these files? If I read the license
>> correctly, then every binary containing the resulting crtbegin.o and
>> crtend.o would have to include a copy of the license with its
>> documentation. If there is such exception, then I'd suggest that
>> the wiki page includes a link to it.
> I'm not aware of this, but you might want to check and see if this
> junk is even needed. My understanding is that these files do nothing
> useful whatsoever unless you're using the old _init/_fini based
> ctor/dtor system. GCC at least has switched to generating __init_array
> and __fini_array which are much saner and I would guess clang has too.
>
> Note that these files aren't needed at all for pure C code anyway,
> only for C++, GNU C, or other langs with static ctors/dtors.
>
> Rich
>
>
Thanks, Rich. From the sources of gcc (4.6 -- 4.8) and llvm/clang (3.4
-- trunk) it appears that gcc introduced __init_array in version 4.7;
when used, __do_global_ctors_aux is absent, however the implementation
of __do_global_dtors_aux is still there (in crtbegin.o).
When clang invokes the linker, it asks for crtbegin.o and crtend.o to be
included regardless of the executable type (c/c++), which might be worth
a patch (clang/lib/Driver/Tools.cpp). On the other hand, it does
support __init_array (by default, I believe, and also through
-fuse-init-array), and there are also relevant bits in the code for
llvm's native linker (lld).
Given that clang also supports the old ctor/dtor system (through
-fno-use-init-array), the status of crtbegin/crtend seems to be still
relevant.
zg
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