[Libunwind-devel] mincore is potentially unsafe on kernel's older than 2.6.21

[Don Maghrak]

Hello,
I recently installed the latest git sources on one of the lab
systems we support which runs a 2.6.18 kernel.  The code
autoreconfed and compiled fine.  But make check yielded 20
failures out of 26 tests. After reviewing the recent commits
I saw that mincore is used over msync in Ginit.c for x86 and
x86_64 systems.

According to the BUGS section in the manpage for mincore on
my fedora 13 laptop):
BUGS
Before kernel 2.6.21, mincore() did not return correct  informa-
tion  for  MAP_PRIVATE  mappings,  or  for  non-linear  mappings
(established using remap_file_pages(2)).

The manpage on the affected linux 2.6.18 system states:
BUGS
Up to now (Linux 2.6.5), mincore() does not return correct information
for MAP_PRIVATE mappings.

I edited include/config.h to undefine HAVE_MINCORE and rebuilt
libunwind. With that the only 4 tests fail (which is what I believe
is the expected failure count for x86_64).

Is there a way to have configure ensure that mincore is only
used at linux 2.6.21 or later?
For now we are undefining HAVE_MINCORE in our builds but that makes
deployment on multiple systems difficult.

thanks,
Don