prgregset_t vs gdb_gregset_t on Linux: not the same!

Daniel Jacobowitz
Sat Jun 9 15:23:00 GMT 2001

On Fri, Jun 08, 2001 at 10:14:52PM -0700, H . J . Lu wrote:
> On Fri, Jun 08, 2001 at 03:59:07PM -0700, Daniel Jacobowitz wrote:
> > On Fri, Jun 08, 2001 at 01:27:30PM -0700, Daniel Jacobowitz wrote:
> > > 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...).
> > 
> > The matching question here is that core-regset.c's fetch_core_registers
> > calls supply_gregset with a gregset_t, but supply_gregset is prototyped
> > with a gdb_gregset_t.  That doesn't work very well either.
> I believe your Linux/MIPS patch is wrong. Please follow the examples in
> linux/alpha, linux/i386 and linux/ppc. Basically, you have to include
> config/tm-linux.h and config/nm-linux.h from the linux/mips header
> files. But in order to do that, please make sure you do

Huh?  Did you even read what I wrote? gdb_gregset_t and
gregset_t/prgregset_t are NOT THE SAME SIZE.

config/nm-linux.h has:
/* Use elf_gregset_t and elf_fpregset_t, rather than
   gregset_t and fpregset_t.  */

#define GDB_GREGSET_T  elf_gregset_t
#define GDB_FPREGSET_T elf_fpregset_t

So gdb_gregset_t is elg_gregset_t.  which, the kernel defines as
an array of 45 elf_greg_t's in <asm/elf.h>.

But prgregset_t is gregset_t
(from <sys/procfs.h>:
 /* Register sets.  Linux has different names.  */
 typedef gregset_t prgregset_t;
 typedef fpregset_t prfpregset_t;

And gregset_t is (<sys/ucontext.h>):
#define NGREG   37
#define NFPREG  33

/* Container for all general registers.  */
/* gregset_t must be an array.  The below declared array corresponds
typedef struct gregset {
        greg_t  g_regs[32];
        greg_t  g_hi;
        greg_t  g_lo;
        greg_t  g_pad[3];
} gregset_t;  */
typedef greg_t gregset_t[NGREG];

> #include <nm-linux.h>
> #include <tm-linux.h>
> not
> #include "nm-linux.h"
> #include "tm-linux.h"
> Otherwise, you may not get the header files you want since mips has
> both liltle and big endians. Once you have done that, your problem
> should go away.

The little endian config files are not named xm-linux.h and tm-linux.h
in a separate directory.  They're named xm-littlelinux.h and

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

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