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

[Youling Tang <tangyouling@loongson.cn>]

Hi, Lancelo

On 03/16/2022 04:42 PM, Lancelot SIX wrote:
> 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).
Ok, I will modify this code style in the next version.

Thanks,
Youling.
> 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
>>