SH4: ADDV instruction not emulated properly
Host environment
- Operating system: Debian testing
- OS/kernel version: 6.7.9
- Architecture: x86_64
- QEMU flavor: qemu-sh4
- QEMU version: qemu-sh4 version 8.2.1 (Debian 1:8.2.1+ds-2)
- QEMU command line:
Emulated/Virtualized environment
- Operating system: Buildroot uClibc (qemu-user)
- OS/kernel version: 6.7.9 (qemu-user)
- Architecture: SH4
Description of problem
ADDV opcode is emulated incorrectly.
The documentation says:
ADDV Rm, Rn Rn + Rm -> Rn, overflow -> T
What Qemu actually emulates:
ADDV Rm, Rn Rn + Rm -> Rm, overflow -> T
Steps to reproduce
#include <stdio.h>
int main(void)
{
register unsigned int a asm("r8") = 0x7fffffff;
register unsigned int b asm("r9") = 1;
register unsigned int c asm("r10");
asm volatile("clrt\n"
"addv %2,%0\n"
"movt %1\n"
: "+r"(a), "=r"(c) : "r"(b) :);
printf("Values: a=0x%x b=0x%x c=0x%x\n", a, b, c);
return 0;
}
Additional information
Tested on real hardware (SEGA Dreamcast, GCC 15.0), the program above prints:
Values: a=0x80000000 b=0x1 c=0x1
Running with Qemu (and GCC 13.0), the same program prints:
Values: a=0x7fffffff b=0x80000000 c=0x1