Re: RFC: Bug 60749 - Do not need to link against -lm for fabs*()

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Walter,

On 09/16/2013 04:57 PM, walter harms wrote:
> 
> 
> Am 14.09.2013 14:05, schrieb walter harms:
>>
>>
>> Am 13.09.2013 20:20, schrieb Michael Kerrisk (man-pages):
>>> Walter,
>>>
>>> On Fri, Sep 13, 2013 at 6:46 PM, walter harms <wharms-fPG8STNUNVg@public.gmane.org> wrote:
>>>> hi list,
>>>> i was investigating this and the good news it that you still need a libm.
>>>> On the other side the reporter is right he does not need to specify that.
>>>> Obviously this depends on the linker script used.
>>>>
>>>> The math man pages say: "Link with -lm".
>>>> Perhaps it is better to say 'You may need to Link with -lm".
>>>>
>>>> any comments on that ?
>>>
>>>
>>> Thanks for looking at this bug. Could you elaborate a little more on
>>> what it/sin't in the linker script that makes the difference?
>>>
>>
>> I have no clue what linker magic is needed.
>>
> I know what it going on. the is no linker magic required.
> The point is gcc build-ins. Some functions are replaced with
> build-ins. That happens e.g. with fabs() what the original poster noted.
> Disabling the build-ins with gcc -fno-builtin shows that the -lm is still
> a requirement.

Thanks! I hadn't thought of that. I see there is a list available in
the gcc documentation at http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html

> next problem, who will do the bugzilla-entry ?

I will add something to https://bugzilla.kernel.org/show_bug.cgi?id=60749
Fundamentally, this is a gcc feature, and I don't think there's much that
can be sensibly said about it in man-pages.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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