Re: Detecting musl at compile and/or configure time

[Szabolcs Nagy <nsz@port70.net>]

* A. Wilcox <awilfox@adelielinux.org> [2019-06-29 08:27:50 -0500]:
> On 06/29/19 06:48, Chris Hall wrote:
> > 
> > Is there a supported way of detecting that one is building against the
> > musl libc ?
> > 
> > At compile time I can, of course, detect glibc because it sets __GLIBC__
> > etc.  For macOS I can see _DARWIN_FEATURE_xxx macros.  The BSDs mostly
> > give themselves away.  But for musl I have not found anything :-(
> > 
> > Chris
> 
> 
> The musl libc specifically does not have a FTM (feature test macro)
> because it aims to be an exact implementation of C11 / POSIX and
> therefore it has no "quirks" to detect.

that's not entirely true.

there are some standard macros in posix to test optional features.

and musl implements various extensions to the standard.

note that __GLIBC__ does not detect glibc: uclibc defines it too.

you really want to configure check for particular features
instead of detecting the libc (which is a moving target,
ppl can patch it or change it over time)

> 
> If there are bugs in musl libc, the authors prefer if you report them
> and have them fixed, instead of making your software look for __MUSL__
> and then assume all musl versions will always have that bug.
> 
> See here for more information:
> 
> https://wiki.musl-libc.org/faq.html#Q:-Why-is-there-no-%3Ccode%3E__MUSL__%3C/code%3E-macro?
> 
> https://www.openwall.com/lists/musl/2013/03/29/13
> 
> Is there a reason you wish to detect musl at configure/compile time?
> Perhaps if we knew the reason, we could help you make your code more
> portable and/or not require such detection.
> 
> Best to you and yours,
> --arw
> 
> 
> -- 
> A. Wilcox (awilfox)
> Project Lead, Adélie Linux
> https://www.adelielinux.org
>