Re: [PATCH] gdb: mips: Fix the handling of complex type of function return value

[Lancelot SIX <lsix@lancelotsix.com>]

On Wed, Mar 16, 2022 at 12:48:26PM +0800, Youling Tang wrote:
> $ objdump -d outputs/gdb.base/varargs/varargs
> 00000001200012e8 <find_max_float_real>:
> ...
>    1200013b8:   c7c10000        lwc1    $f1,0(s8)
>    1200013bc:   c7c00004        lwc1    $f0,4(s8)
>    1200013c0:   46000886        mov.s   $f2,$f1
>    1200013c4:   46000046        mov.s   $f1,$f0
>    1200013c8:   46001006        mov.s   $f0,$f2
>    1200013cc:   46000886        mov.s   $f2,$f1
>    1200013d0:   03c0e825        move    sp,s8
>    1200013d4:   dfbe0038        ld      s8,56(sp)
>    1200013d8:   67bd0080        daddiu  sp,sp,128
>    1200013dc:   03e00008        jr      ra
>    1200013e0:   00000000        nop
> 
> From the above disassembly, we can see that when the return value of the
> function is a complex type and len <= 2 * MIPS64_REGSIZE, the return value
> will be passed through $f0 and $f2, so fix the corresponding processing
> in mips_n32n64_return_value().
> 
> $ make check RUNTESTFLAGS='GDB=../gdb gdb.base/varargs.exp --outdir=test'
> 
> Before applying the patch:
>  FAIL: gdb.base/varargs.exp: print find_max_float_real(4, fc1, fc2, fc3, fc4)
>  FAIL: gdb.base/varargs.exp: print find_max_double_real(4, dc1, dc2, dc3, dc4)
> 
>  # of expected passes		9
>  # of unexpected failures	2
> 
> After applying the patch:
>  # of expected passes            11
> 
> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
> ---
>  gdb/mips-tdep.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
> index 7e37578..cddb8f8 100644
> --- a/gdb/mips-tdep.c
> +++ b/gdb/mips-tdep.c
> @@ -5224,9 +5224,10 @@ mips_n32n64_return_value (struct gdbarch *gdbarch, struct value *function,
>  
>    if (TYPE_LENGTH (type) > 2 * MIPS64_REGSIZE)
>      return RETURN_VALUE_STRUCT_CONVENTION;
> -  else if (type->code () == TYPE_CODE_FLT
> +  else if ((type->code () == TYPE_CODE_FLT
>  	   && TYPE_LENGTH (type) == 16
>  	   && tdep->mips_fpu_type != MIPS_FPU_NONE)

Hi,

Just minor note, those 2 lines above should be indented 2 more space I
think (so the && operator continues to vertically align with "type->code
()").

> +	   || (type->code () == TYPE_CODE_COMPLEX))

I do not think the extra set of parens are requires (but they do no harm
either).

For the rest, it seems reasonable to me but I’ll let MIPS / global
maintainers comment.

Best,
Lancelot.
>      {
>        /* A 128-bit floating-point value fills both $f0 and $f2.  The
>  	 two registers are used in the same as memory order, so the
> -- 
> 2.1.0
> 

-- 
Lancelot SIX