Re: Bug in PPC inline assembly?

[Stefan <stefan dot 74 at comhem dot se>]

Thanks for your help: using constraint "b" instead of "r" solved my problem.

-- Stefan


> Try using 'b' for the constraint - that selects for an "address base
> register", as opposed to 'r' that is any of the general registers 
(including
> R0)

>> I have some problems with using inline PowerPC assembly in GCC (4.0.1).
>> Consider the following code:
>>
>>    void save_fp_register(double* buffer)
>>    {
>>        asm("stfd F0,  0(%0)" : : "r" (buffer) );
>>    }
>>
>> When compiled with -Os the generated code becomes
>>
>>    save_fp_register:
>>        stfd F0,  0(3)
>>        blr
>>
>> Which is OK; the input parameter comes in r3 which is used directly 
in the
>> stfd operation. However, when compiled with -O0 (no optimization) the
>> generated code instead becomes
>>
>>    save_fp_register:
>>        stwu 1,-24(1)
>>        stw 31,20(1)
>>        mr 31,1
>>        stw 3,8(31)
>>        lwz 0,8(31)
>>        stfd F0,  0(0) <-- error
>>        lwz 11,0(1)
>>        lwz 31,-4(11)
>>        mr 1,11
>>        blr
>>
>> The input parameter r3 is transferred to r0, which is used in the stfd
>> operation. However, for this particular operation r0 means 0 -- not 
the value
>> stored in r0 -- which means that the machine will actually try to 
store the
>> value at address 0x0.
>>
>> Is this a bug in GCC or is it my code that is messed up?