[Qemu-devel] [Bug 617528] Re: Incorrect translation of unary PPC/SPE instructions (efdneg etc.)

[Aurelien Jarno]

** Changed in: qemu
       Status: Fix Committed => Fix Released

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/617528

Title:
  Incorrect translation of unary PPC/SPE instructions (efdneg etc.)

Status in QEMU:
  Fix Released

Bug description:
  The translation for the following PPC/SPE (e500) instructions is wrong
  in QEMU git 6cbf4c8c:

      evfsabs, evfsnabs, evfsneg
      efdabs, efdnabs, efdneg
      efsabs, efsnabs, efsneg

  As you can see from the provided patch, these ought to write their
  result to the destination register (rD) and not modify the source
  register (rA) in-place.

  It's rather hard to generate a test-case for this with GCC, since it
  likes to put the input and output of a unary operation into the same
  registers (that's probably also the reason why this went unnoticed).
  There is however a broken code path in the EGLIBC function for sin()
  when compiled for e500v2. It returns nonsense results for e.g. -1.0.
  Trivial test code follows:

      #include <stdio.h>
      #include <stdlib.h>
      #include <math.h>

      int main(int argc, char **argv)
      {
        double x = strtod(argv[1], NULL);
        printf("%.14g\n", sin(x));
        return 0;
      }

  Result before the patch (WRONG):

  $ qemu-ppc -cpu e500v2 sintest -1.0
  -1

  Result after the patch (OK):

  $ qemu-ppc -cpu e500v2 sintest -1.0
  -0.84147071838379

  A self-contained test-case using inline assembler can be provided upon
  request.