prgregset_t vs gdb_gregset_t on Linux: not the same!

Daniel Jacobowitz
Fri Jun 8 13:27:00 GMT 2001

In proc-service.c, we call fill_gregset and supply_gregset with a
prgregset_t cast to a gdb_gregset_t *.  The problem is, they really are
different.  We can mostly get away with this, because in almost all cases
glibc won't do anything with the gregset except pass it back to gdb again
(if the process has terminated, it will memset something the size of a
prgregset_t, though...).

Now for the reason it's a problem: I don't have any idea where this
definition came from, but a prgregset_t on Linux/MIPS is smaller than an
elf_gregset_t by a considerable amount.  This caused me no end of confusion
while I was trying to add threads support to the MIPS port (which I've just
started feeding back patches for today).

Of course, the thread_db functions are defined to take a prgregset_t, so
it's unclear what we really can do.  Make sure we always allocate the size
of the larger one, perhaps, and assume glibc won't do too much damage?

The prgregset_t type unfortunately is one word too small for all the
registers we can get from ptrace(), even if I fill its pad words with data.

Daniel Jacobowitz                           Debian GNU/Linux Developer
Monta Vista Software                              Debian Security Team

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