Re: mmap use in linuxthreads

[Wolfram Gloger <wmglo at dent dot med dot uni-muenchen dot de>]

Hello,

> I was pointed at a problem with the way we are using mmap() within
> libpthread. It seems that the Linux kernel will kill an existing mapping
> silently if you try to mmap(MAP_FIXED) on a range overlaying an existing
> mapping for a task. According to SUSv2 this seems to be within spec
> (http://www.opengroup.org/public/pubs/online/7908799/xsh/mmap.html):

Yes, this is perfectly OK, I'm pretty sure most if not all Unices do this.

> However linuxthreads/manager.c seems to rely on mmap() returning
> MAP_FAILED in case you have a conflict, for instance this part:
..
> Hence the question is what to do here, should one try to fix
> linuxthreads to check for a conflict before trying a mapping or lobby
> for the kernel to be changed?

I'm currently looking into this.  It has been pointed out on bug-glibc
that Linux obeys the hint given by specifying an addr argument without
MAP_FIXED as long as the area is unmapped, which is very useful here.
So I'm working on a patch that makes use of this fact.

Regards,
Wolfram.