From: Roland McGrath <roland@redhat.com>

gdb really needs some way to know the AT_SYSINFO_EHDR value for a process
being debugged or for the dead process described by a core file.  Without
this value, it can't find the information necessary to show backtraces of
threads waiting in system calls.  There are any number of ways this
information could be made available.  Here is one solution that provides
more debugging information in a clean and general fashion.

I've added access to the AT_* values passed to a process for third parties
to examine for debugging purposes.  The same data passed on the stack at
startup is made available in /proc/PID/auxv and is written in an NT_AUXV
note in core dumps.  (Both of these are consistent with what Solaris does
using the same names.)

Here are two different patches that implement the same thing differently.
The first patch uses a ref-counted data structure to copy the aux vector
and shares among forked mm's until they exec and get a new one.  The second
patch avoids the complexity of that data structure by simply expanding the
mm_struct with space to hold a copy of the data.  Both patches work
correctly; I have examined the new /proc/PID/auxv file and core dumps.

I hope you will consider including one of these patches, or at least some
way of getting at this information from the debugger.  I am certainly open
to other suggestions on implementing this feature, and to suggestions on
alternative interfaces for getting the AT_SYSINFO_EHDR value cleanly.