Re: [RFA/commit/ia64-linux] Allow libunwind to fetch register 0

[Pedro Alves <pedro@codesourcery.com>]

On Tuesday 25 October 2011 17:52:43, Joel Brobecker wrote:

>  gdb/ia64-linux-nat.c |   11 +++++++++++
>  1 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/gdb/ia64-linux-nat.c b/gdb/ia64-linux-nat.c
> index 65e077b..f43e91e 100644
> --- a/gdb/ia64-linux-nat.c
> +++ b/gdb/ia64-linux-nat.c
> @@ -681,6 +681,17 @@ ia64_linux_fetch_register (struct regcache *regcache, int regnum)
>    PTRACE_TYPE_RET *buf;
>    int pid, i;
>  
> +  /* r0 cannot be fetched but is always zero.  */
> +  if (regnum == 0)

IA64_GR0_REGNUM?

> +    {
> +      const char r0_value[8] = {0x00, 0x00, 0x00, 0x00,
> +				0x00, 0x00, 0x00, 0x00};

FYI, in C, this is equivalent to:

        const char r0_value[8] = { 0 };

I'd write it as:

        const char zero[8] = { 0 };

> +
> +      gdb_assert (sizeof (r0_value) == register_size (gdbarch, regnum));
> +      regcache_raw_supply (regcache, regnum, r0_value);
> +      return;
> +    }
> +

I don't speak ia64, but this is the right direction.
I think we should make ia64_cannot_fetch_register return true for
gr0 too though.  Your new code in ia64_linux_fetch_register would
then be moved a bit further down after the ia64_cannot_fetch_register
check.  It may be there's no code that trip on the below issue,
but it's best to avoid leaving the issue latent.

-- 
Pedro Alves