Re: [PATCH v3 1/2] ppc: use "trap" ("tw, 31, 0, 0") as breakpoint instruction

[Joel Brobecker <brobecker@adacore.com>]

Hi Jan,

On Wed, Dec 01, 2021 at 02:30:04PM +0000, Jan Vrany wrote:
> Power ISA 3.0 B spec [1], sections 3.3.11 "Fixed-Point Trap Instructions"
> and section C.6 "Trap Mnemonics" specify "tw, 31, 0, 0" (encoded as
> 0x7fe00008) as canonical unconditional trap instruction.
> 
> This commit changes the breakpoint instruction used by GDB from
> "tw 12, r2, r2" to unconditional "trap".
> 
> [1]: https://openpowerfoundation.org/?resource_lib=power-isa-version-3-0

Thanks for the additional reference. This looks good to me, and
I think it's can be pushed independently of patch #2.

> ---
>  gdb/rs6000-tdep.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index 87a494e0bb8..43880fa4426 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -824,8 +824,8 @@ rs6000_fetch_pointer_argument (struct frame_info *frame, int argi,
>  
>  /* Sequence of bytes for breakpoint instruction.  */
>  
> -constexpr gdb_byte big_breakpoint[] = { 0x7d, 0x82, 0x10, 0x08 };
> -constexpr gdb_byte little_breakpoint[] = { 0x08, 0x10, 0x82, 0x7d };
> +constexpr gdb_byte big_breakpoint[] = { 0x7f, 0xe0, 0x00, 0x08 };
> +constexpr gdb_byte little_breakpoint[] = { 0x08, 0x00, 0xe0, 0x7f };
>  
>  typedef BP_MANIPULATION_ENDIAN (little_breakpoint, big_breakpoint)
>    rs6000_breakpoint;
> -- 
> 2.30.2
> 

-- 
Joel