Re: [Qemu-ppc] [Qemu-devel] Floating point unit bugs

[G 3]

On May 8, 2017, at 6:13 PM, Aurelien Jarno wrote:

> On 2017-05-07 17:48, G 3 wrote:
> > I made a diagnostic program for the floating point unit. It will test
> > various PowerPC floating point instructions for compatibility with  
> > the
> > PowerPC G3 processor. It was tested on a PowerPC G3 and G5 system.  
> > The
> > results of the program in qemu-system-ppc were pretty bad. About  
> > every
> > instruction tested is not implemented correctly.
> >
> > Here is the download link to the program: http://www.mediafire.com/ 
> > file/6j9tqubvk73lkw1/floating_point_test_program.zip
>
> Some comments on the code.
> >     /* Check if everything is alright */
> >     uint32_t fpscr;
> >     asm volatile("mffs f0");
> >     asm volatile("stfd f0, 40(r1)");
> >     asm volatile("lwz %0, 44(r1)" : "=r"(fpscr));
> >     if (fpscr != 0) {
> >         printf("Warning: fpscr not equal to zero: 0x%x\n", fpscr);
> >     }
>
> This is overly complicated and just doesn't compile with recent GCC
> versions.

Which version of GCC had the problem? GCC 5.2 and GCC 3.3 seems to  
work fine. GCC 4.0 did not work. Could you send me the error message?

> What about something like:
>
>     Converter c;
>     asm volatile("mffs %0" : "=f"(c.d));
>     fpscr = (uint32_t)c.i;

This way does work also.

> > /*
> >  * The action to take if a test fails
> >  * Input one: message string
> >  * Input two: actual fpscr value
> >  * Input three: expected fpscr value
> >  * Input four: actual answer
> >  * Input five: expected answer
> >  */
> >  void test_failed(const char *message, uint32_t actual_fpscr,  
> > uint32_t
> > expected_fpscr,
> >                   uint64_t actual_answer, uint64_t expected_answer)
> >  {
> >     printf("%s\n", message);
> >     printf("expected answer: 0x%" PRIx64 "\n", expected_answer);
> >     printf("  actual answer: 0x%" PRIx64 "\n", actual_fpscr);
>
> This is wrong. It should be actual_answer instead of actual_fpscr.  
> That
> is why all the instructions seems totally wrongly implemented.

Thanks for catching this error. Actually this would only effect the  
"actual answer:" output field. The comparison between expected_answer  
and actual_answer in each individual test is still valid.

> Note that
> compiling with -Wall would give you a warning:
>
> | main.c: In function ‘test_failed’:
> | main.c:146:5: warning: format ‘%llx’ expects argument of type  
> ‘long long unsigned int’, but argument 2 has type ‘uint32_t’ [- 
> Wformat=]
> |      printf("  actual answer: 0x%" PRIx64 "\n", actual_fpscr);
> |      ^

Replacing actual_fpscr with actual_answer should solve this problem.