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[[!tag open_issue_glibc]]
[[!sourceware_PR 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 [[!message-id
"20120720162519.734e02eb@spoyarek"]] touches related topics.
2011-07: This is what Samuel has [done for Debian
glibc](http://anonscm.debian.org/viewvc/pkg-glibc/glibc-package/trunk/debian/patches/hurd-i386/local-madvise_warn.diff).
# 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
you/Debian/...?
<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.
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