Date: Sun, 20 Sep 2020 13:14:46 -0400 From: Rich Felker <dalias@...c.org> To: Bruno Haible <bruno@...sp.org>, "Dmitry V. Levin" <ldv@...linux.org>, config-patches@....org, musl@...ts.openwall.com Subject: Re: Re: OS detection wrong on Alpine Linux 3.10 On Sun, Sep 20, 2020 at 03:56:29PM +0200, Szabolcs Nagy wrote: > * Bruno Haible <bruno@...sp.org> [2020-09-20 13:19:13 +0200]: > > Dmitry V. Levin wrote: > > > Is this __DEFINED_va_list macro the official way of detecting musl? > > > > No, but in a world where the musl people don't want to provide an official > > way  and the Alpine Linux people break their previously working way of > > detecting musl , we (GNU) need to use our own heuristics to fulfil the > > practical need of programs (especially test suites) to distinguish musl > > systems from glibc systems. > > we have not seen a "practical need of programs > to distinguish musl systems from glibc systems". > > instead we have seen a practical need to detect > specific c runtime behaviours and extensions. > > even in the glibc world using __GLIBC__ to detect > features is not reliable since there are heavily > patched glibcs out there. (though the way glibc > handles api and abi stability means it mostly > works, but this is unreasonable to expect across > different implementations) There is one kinda legitimate purpose for detecting specifically musl: when setting $target to match $host for the purpose of a host-targeting compiler toolchain. That does not seem to be the topic at hand here, though. Please note that __DEFINED_* are bits/alltypes.h-internal macros, and are not public interfaces for detecting musl or definition status of any particular type. They are not even "public within musl" -- i.e. musl source files or public headers outside bits/alltypes.h are not allowed to use or poke at them. Their naming or the entire mechanism is subject to change at any time. Rich
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