Hi,
I tested the following with the qemu git HEAD as of 2013-09-30 on Debian stable and testing. My host runs amd64 but I also tried this out inside a i386 chroot with the same result. The problem occurs for mips and mipsel. Given the following program:
#include <stdio.h>
int main(int argc, char **argv)
{
int a = 1;
double d = a/2.0;
printf("%f\n", d);
return 0;
}
Instead of printing 0.5, it will print 2.0 if executed in qemu user mode.
$ mipsel-linux-gnu-gcc mipstest.c
$ ~/qemu/mipsel-linux-user/qemu-mipsel ./a.out
2.0
Expecting this to be a problem with my cross compiler (gcc-4.4 from emdebian) I ran a fully emulated debian squeeze environment inside qemu. There, I compiled the same program natively with gcc and as expected got 0.5 as the output. I also copied the cross compiled binary inside the emulated environment and also got 0.5 when I ran it. So the same mips/mipsel binary produces different output depending on whether it is run in a fully emulated environment or qemu user mode.
Can anybody else reproduce this problem?
I can confirm that something is strange with MIPS Linux user emulation, but get a different result (which is also wrong):
# Your test code is in file divtest.c.
$ mipsel-
$ mipsel-
0.000000
Some more tests:
printf("%f\n", a * 1.0); // 0.000000 = bad
printf("%f\n", (double)a); // 0.000000 = bad
printf("%f\n", 1.0); // 1.000000 = good
Test environment:
* latest QEMU sources + default configure & make on x86_64 Debian squeeze host
* gcc-4.7-