Public bug reported:
I'm using qemu-3.1.0 (Gentoo).
When I was running regression test suite via qemu-ppc for GHC I noticed
a few uint32_t<->float32 failures I did not expect to encounter.
Here is an example
$ cat a.c
#include <stdio.h>
#include <stdint.h>
int main() {
volatile uint32_t i = 1;
printf("0x1 = %e\n", *(volatile float*)&i);
}
$ powerpc-unknown-linux-gnu-gcc -O2 a.c -Wall -o a -fno-strict-aliasing
-fno-stack-protector -static && ./a
0x1 = 2.802597e-45
$ scp a timberdoodle.ppc64.dev.gentoo.org:~/
a
100% 826KB 102.0KB/s 00:08
$ ssh timberdoodle.ppc64.dev.gentoo.org ./a
0x1 = 1.401298e-45
$ qemu-ppc ./a
0x1 = 2.802597e-45
Looks like off-by-one bit somewhere. I'm not sure if it's FPU
instruction or some internals of printf() that are emulated incorrectly.
** Affects: qemu
Importance: Undecided
Status: New
** Attachment added: "statically linked example"
https://bugs.launchpad.net/bugs/1821444/+attachment/5248800/+files/a-ppc
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https://bugs.launchpad.net/bugs/1821444
Title:
qemu-ppc (user) incorrectly translates float32 arithmetics
Status in QEMU:
New
Bug description:
I'm using qemu-3.1.0 (Gentoo).
When I was running regression test suite via qemu-ppc for GHC I
noticed a few uint32_t<->float32 failures I did not expect to
encounter.
Here is an example
$ cat a.c
#include <stdio.h>
#include <stdint.h>
int main() {
volatile uint32_t i = 1;
printf("0x1 = %e\n", *(volatile float*)&i);
}
$ powerpc-unknown-linux-gnu-gcc -O2 a.c -Wall -o a -fno-strict-aliasing
-fno-stack-protector -static && ./a
0x1 = 2.802597e-45
$ scp a timberdoodle.ppc64.dev.gentoo.org:~/
a
100% 826KB 102.0KB/s 00:08
$ ssh timberdoodle.ppc64.dev.gentoo.org ./a
0x1 = 1.401298e-45
$ qemu-ppc ./a
0x1 = 2.802597e-45
Looks like off-by-one bit somewhere. I'm not sure if it's FPU
instruction or some internals of printf() that are emulated
incorrectly.
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