Re: [Qemu-devel] [PATCH] gdbstub/ppc: handle read and write of fpscr

[Tristan Gingold]

On Feb 15, 2011, at 11:22 AM, Peter Maydell wrote:

> On 15 February 2011 08:59, Tristan Gingold <address@hidden> wrote:
>> @@ -770,7 +770,8 @@ static int cpu_gdb_write_register(CPUState *env, uint8_t 
>> *mem_buf, int n)
>>             /* fpscr */
>>             if (gdb_has_xml)
>>                 return 0;
>> -            return 4;
>> +            env->fpscr = ldtul_p(mem_buf);
>> +            return sizeof(target_ulong);
>>         }
>>     }
>>     return 0;
> 
> Not a PPC expert, but this doesn't look right; for instance if you change
> the rounding mode by fiddling with the FPSCR in the debugger this
> won't update the softfloat rounding mode settings. (that is, it lets the
> visible state in env->fpscr get out of sync with the hidden state of the
> model). Also we probably shouldn't be letting the debugger change
> reserved fpscr bits.

Indeed, you're right.  We initially were interested in reading fpscr, and I 
wrote the writing part without thinking enough.

Tristan.