README for Red Hat Linux 9.0



There is a GNAT 3.15p incompatibility with the default pthread library that
is utilized by Red Hat 9.0 on Intel CPUs designated as i686's.  The i686
processors include the Pentium 2, 3, and 4 (for comparison, the i586
consists of the original Pentium and Pentium Pro).  Since DTraq does GNAT
compilations as part of its logging server generation, this incompatibility
affects DTraq.

The root of the problem lies with GNAT 3.15p's interaction with the Native
Posix Thread Library (NPTL) implementation of libpthread.  Any GNAT 3.15p
Ada program that employs tasking will freeze when the executable is linked
with this version of the library.

This version of libpthread is present as /lib/tls/libpthread.so.0.

To determine if your locked-up program is using this library, invoke the
ldd command on your executable:

$ ldd executable

and check the output for an appearance of the above library path.

The best alternative to the NPTL on the affected CPUs, until a new version
of GNAT is available that does not have the problem, is to use the
LinuxThreads versions of libthread.  While this version is present as
/lib/i686/libpthread.so.0, it appears that specifying the use of that
version cannot be explicitly done as part of the linking process.  However,
setting the environment variable LD_ASSUME_KERNEL for the user that does
GNAT 3.15p compilations (including the DTraq user) to the appropriate value
will cause the linker to use the LinuxThreads version of the library.

LD_ASSUME_KERNEL can be set as follows, with the specified effect:

export LD_ASSUME_KERNEL=2.4.1	(bash)
setenv LD_ASSUME_KERNEL 2.4.1	(csh, tcsh)
	"forces" LinuxThreads on i686 -- you'll get
        /lib/i686/libpthread.so.0

export LD_ASSUME_KERNEL=2.2.5	(bash)
setenv LD_ASSUME_KERNEL 2.2.5	(csh, tcsh)
	"forces" the i586 version from /lib/lipthread.so.0

For a concise summation of this issue, see the comp.programming.threads
posting by Paul Pluzhnikov at

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=uel0sqyq8.fsfYB8X%40earthlink.net


Marc A. Criley
McKae Technologies

Last updated: 7 Aug 2003