diff options
Diffstat (limited to 'results/classifier/accel-gemma3:12b/kvm/493')
| -rw-r--r-- | results/classifier/accel-gemma3:12b/kvm/493 | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/results/classifier/accel-gemma3:12b/kvm/493 b/results/classifier/accel-gemma3:12b/kvm/493 new file mode 100644 index 000000000..3d15113cb --- /dev/null +++ b/results/classifier/accel-gemma3:12b/kvm/493 @@ -0,0 +1,8 @@ + +RISC-V: Setting mtimecmp to -1 immediately triggers an interrupt +Description of problem: +When setting mtimecmp to -1, which should set a timer infinitely far in the future, a timer interrupt is triggered immediately. This happens for most values over 2^61. It is the same for both 32-bit and 64-bit, and for M-mode writing to mtimecmp directly and S-mode using OpenSBI. + +I have looked through the source code, and the problem is in the function `sifive_clint_write_mtimecmp`, in the file `/hw/intc/sifive_clint.c`. First, the muldiv64 multiplies diff with 100, causing an overflow (at least for -M virt, other machines might use a different timebase_freq). Then, the unsigned `next` is passed to `timer_mod`, which takes a signed integer. In `timer_mod_ns_locked` the value is set to `MAX(next, 0)`, which means that if the MSB of `next` was set, the interrupt happens immediately. This means that it is impossible to set timers more than 2^63 nanoseconds in the future. + +This problem basically only affects programs which disable timer interrupts by setting the next one infinitely far in the future. However, the SBI doc specifically says that this is a valid approach, so it should be supported. Using the MSB doesn't work without changing code functionality in QEMU, but it should be sufficient to cap `next` at the maximum signed value. |