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From: Lei Zhang <zhanglei.april@gmail.com>
Date: Wed, 15 Jun 2016 09:45:19 +0800
Message-ID: <CAOYuCc3ZyA0SS1EUpVMGYmNrTUSX3k69d4Jz7dz2iYW1fQkF_A@mail.gmail.com>
Subject: Re: [gentoo-musl] [GSoC] _GNU_SOURCE in C++
To: Luca Barbato <lu_zero@gentoo.org>
Cc: gentoo-musl@lists.gentoo.org
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This issue is probably not as simple as I thought. Supposing C++
header iostream depends on some non-standard functions from stdio.h,
it may look like:
// iostream
#define _BSD_SOURCE
#include <stdio.h>
#undef _BSD_SOURCE
...
But if a user writes some code like:
// user code
#include <stdio.h>
#include <iostream> // stdio.h already expanded before this point
...
then iostream never has the chance to get those non-standard symbols,
*unless* the compiler predefines _BSD_SOURCE for it. So simply
patching libc++/libstdc++ doesn't work; you have to carefully choose
which visibility macros to predefine in the compiler. And predefining
_GNU_SOURCE is just the safest bet.
I don't see any easy fix for this at the moment :(
Lei
2016-06-14 20:03 GMT+08:00 Luca Barbato <lu_zero@gentoo.org>:
> On 14/06/16 13:48, Lei Zhang wrote:
>> 2016-06-14 19:18 GMT+08:00 Luca Barbato <lu_zero@gentoo.org>:
>>> On 14/06/16 11:35, Lei Zhang wrote:
>>>> I agree. It seems libstdc++ is also taking the lazy route, and someone
>>>> intended to fix it:
>>>>
>>>> https://lwn.net/Articles/590504/
>>>>
>>>> but I see no progress so far.
>>>>
>>>
>>> make -k and let's try to extract the list of missing symbols from it.
>>
>> A quick test with libc++:
>>
>> aligned_alloc
>
> aligned_alloc(): _ISOC11_SOURCE
>
>> atoll
>
> atoll():
> _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
> _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
>
>> _Exit
>
> _Exit():
> _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >=
> 200112L;
>
>> fwide
>
> fwide():
> _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE ||
> _POSIX_C_SOURCE >= 200112L;
>
> etc etc etc
>
> try to figure out which defines correctly enable those and send patches
> to be precise =)
>
> lu
>
>
>