Re: *gregset_t misuse (was Re: S390 GDB patch for Dignus Linux/390 compiler support)

[Daniel Jacobowitz <drow at mvista dot com>]

On Mon, Mar 18, 2002 at 10:58:16AM -0500, Greg Alexander wrote:
> I'm having a hard time figuring out how exactly the ps_l{get,set}regs()
> and thread_db_{fetch,store}_registers() functions get used, but my
> proposal would be for them to use gdb_gregset_t instead of prgregset_t
> (so that gdb_gregset_t can be defined to a pointer type if necessary --
> prgregset_t is really an arch-specific type and should only be referenced
> inside of arch-aware files).  I also propose that fill_gregset() and

No.  ps_lgetregs is not a gdb-called function.  It's called from
libthread_db.so, which is provided by the system.  Its argument must be
a prgregset_t.  Therefore prgregset_t must also be a pointer or array type.

> It all comes down to the fact that gdb_gregset_t will probably be typedefed
> to prgregset_t or prgregset_t*, but never both!

Remember what I said?  From an i386-linux <sys/procfs.h>:

/* And the whole bunch of them.  We could have used `struct
   user_regs_struct' directly in the typedef, but tradition says that
   the register set is an array, which does have some peculiar
   semantics, so leave it that way.  */
#define ELF_NGREG (sizeof (struct user_regs_struct) / sizeof(elf_greg_t))
typedef elf_greg_t elf_gregset_t[ELF_NGREG];


S/390 needs to do the same thing.  It's very hard to compensate for an
incorrect prgregset_t, because of some peculiarities in the type system
of C w.r.t. arrays and pointer decay.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer