This is a version of the tcore multi-threaded core dump patch that supports
both i386 and ia64 architectures.  

Its been smoke tested on a 2 way IPF box, it doesn't seem to crash ;)

I'm new to the stack unwinding thing WRT ia64 and would love to get some
feed back on my tweaks to process.c that collect the register state data for
the thread processes in the crashing thread group.  

This multithread core dump is very similar to the patches I've been tossing
up to the LKML, only this one supports ia64 core dumps as well as i386.  

This patch applies cleanly to the 2.5.10+ia64 kernel.
It has a off by 2 line offset warnings in binfmt_elf.c for the stock 2.5.10
kernel due to some include lines added to binfmt_elf.c by the ia64 patch.  I
build this patch against the ia64 kernel.  Regardless, it works for both
architectures.

To use this patch you need to "echo 1 > /proc/sys/kernel/core_dumps_threads"
to enable the tcore code path.  Then when a multi-threaded application dumps
core, it will crate a core file with the data for all the processes in the
thread group.

This code works by "suspending" the other thread group processes, and then
adding extra note sections to the core file with the user register state
data.  GDB 5.x knows how to work with these core files with one caveat.  You
may need to "strip libpthread*" before loading up the core file and crashing
application into gdb.  GDB 5.x; x < 2,  seems to have a problem loading
symbols for libpthread in this type of use.

The process suspend design does a number of interesting things that are
worth pointing out.
1) it creates an extra run queue that has no cpu, the phantom cpu.
2) it uses process migration to migrate the processes of the thread group to
the phantom run queue.
3) it removes the down_write from elf_dump_core, to avoid any possibility of
deadlocking with one of the suspended thread processes.  This is safe to do
as the other thread process are suspended and cannot free pages while they
aren't getting any CPU time.

One last note, I would have made this patch against the 2.5.18-ia64, but I
was missing a header file (perfmon_itanium.h) and had some problems building
it. 

--mgross

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