sourceware [BZ #4822].

$ echo 'int main() {}' | gcc -o /dev/null -static -x c -
/usr/lib/gcc/i486-gnu/4.4.5/../../../libcrt.a(malloc.o): In function `_int_free':
(.text+0xdc3): warning: warning: madvise is not implemented and will always fail

This is correct, but it does confuse GNU Autoconf, for example, which then thinks that static linking is not supported and sets a flag accordingly, which luckly no / not many packages use.

This call does not influence the semantics of the application (except in the case of MADV_DONTNEED), but may influence its performance. The kernel is free to ignore the advice. (man madvise), so we may simply want to turn it into a no-op in glibc, avoiding the link-time warning.

GCC c5db973fdab3db3e13db575e5650c0bcfd3630f4 (2011-10-17) makes use of this. As we now export the symbol (and MADV_DONTNEED, too), GCC will no longer munmap pages, but will keep them mapped for later re-use. This may increase memory usage. The discussion in id:"20120720162519.734e02eb@spoyarek" touches related topics.

2011-07: This is what Samuel has done for Debian glibc.

IRC, freenode, #hurd, 2012-02-16

<tschwinge> youpi: With Roland's fix the situation will be that just using
  gcc -static doesn't emit the stub warning, but still will do so in case
  that the source code itself links in madvise.  Is this acceptable for
<youpi> packages with -Werror will still bug out
<youpi> not that I consider -Werror to be a good idea, though :)
<tschwinge> youpi: Indeed.  Compiler warnings can be caused by all kinds of
  things.  -Werror is good for development, but not for releases.