Public bug reported:
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.
** Affects: qemu
Importance: Undecided
Status: New
--
Incorrect translation of unary PPC/SPE instructions (efdneg etc.)
https://bugs.launchpad.net/bugs/617528
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Status in QEMU: New
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.
