Re: [PATCH] xtensa: initialize call_abi in xtensa_tdep

[Joel Brobecker <brobecker@adacore.com>]

On Sun, Jun 07, 2015 at 01:05:36AM +0300, Max Filippov wrote:
> Use XSHAL_ABI value provided by xtensa-config.h to correctly initialize
> xtensa_tdep.call_abi
> This fixes calls to functions from GDB that otherwise fail with the
> following assertion in call0 configuration:
> 
>   gdb/regcache.c:602: internal-error: regcache_raw_read: Assertion
>   `regnum >= 0 && regnum < regcache->descr->nr_raw_registers' failed.
> 
> gdb/
> 	* xtensa-tdep.h (XTENSA_GDBARCH_TDEP_INSTANTIATE): Initialize
> 	call_abi using XSHAL_ABI macro.

I am not sure I understand the patch.

The first thing I should mention is that, unless what your patch
suggests, the code as I see it on master currently initializes call_abi
to CallAbiDefault:

          .call_abi = CallAbiDefault,                           \

And looking at the definitions of XSHAL_ABI and XTHAL_ABI_CALL0
in include/xtensa-config.h, those definitions seem to be entirely
static...

    #undef XSHAL_ABI
    #undef XTHAL_ABI_WINDOWED
    #undef XTHAL_ABI_CALL0
    #define XSHAL_ABI                       XTHAL_ABI_WINDOWED
    #define XTHAL_ABI_WINDOWED              0
    #define XTHAL_ABI_CALL0                 1

... and resolving to distinct values. So the condition would always
be false, resulting in call_abi always being set to CallAbiDefault.

Am I missing something?

>  gdb/xtensa-tdep.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/xtensa-tdep.h b/gdb/xtensa-tdep.h
> index adacaf8..3b6ea66 100644
> --- a/gdb/xtensa-tdep.h
> +++ b/gdb/xtensa-tdep.h
> @@ -246,7 +246,8 @@ struct gdbarch_tdep
>  	  .spill_location = -1,					\
>  	  .spill_size = (spillsz),				\
>  	  .unused = 0,						\
> -	  .call_abi = 0,					\
> +	  .call_abi = (XSHAL_ABI == XTHAL_ABI_CALL0) ?		\
> +		CallAbiCall0Only : CallAbiDefault,		\

Small style issue: binary operators should be at the start of
the next line, rather than the end of the current line.

Also, for multi-line conditions like that, the GNU Coding Standard
asks that we help automatic code formatters by wrapping the expression
inside parentheses. These are redundant for the compiler, but help
code formatters. Since the parens around the == operator are unecessary,
I would have written the above:

	  .call_abi = (XSHAL_ABI == XTHAL_ABI_CALL0		\
                       ? CallAbiCall0Only : CallAbiDefault),	\

People sometime even write it as the following, finding it clearer
(although a matter of taste, of course):

	  .call_abi = (XSHAL_ABI == XTHAL_ABI_CALL0		\
                       ? CallAbiCall0Only			\
                       : CallAbiDefault),			\

I personally have no preference.

>  	  .debug_interrupt_level = XCHAL_DEBUGLEVEL,		\
>  	  .icache_line_bytes = XCHAL_ICACHE_LINESIZE,		\
>  	  .dcache_line_bytes = XCHAL_DCACHE_LINESIZE,		\
> -- 
> 1.8.1.4

-- 
Joel