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Kernel/riscv64: Increment sepc before re-enabling interrupts

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This otherwise caused a race condition between the signal dispatcher
(which sets sepc to the signal trampoline) and sepc being updated in the
trap handler.
We obviously have to keep the sepc set by the signal dispatcher and not
increment it afterwards.
This commit is contained in:
Sönke Holz 2024-04-17 12:33:22 +02:00 • committed by Andrew Kaster
commit 6cd130ec8e
Notes: sideshowbarker 2024-07-16 22:34:39 +09:00
1 changed files with 5 additions and 1 deletions
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6
Kernel/Arch/riscv64/Interrupts.cpp
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@ -42,6 +42,11 @@ extern "C" void trap_handler(TrapFrame& trap_frame)
{
auto scause = trap_frame.regs->scause;
// sepc has to point to the instruction following the ecall when returning from a syscall, unless it is changed by the syscall handler.
// We have to increment sepc before interrupts are re-enabled, as code triggered by interrupts also can cause sepc to be updated.
if (scause == RISCV64::CSR::SCAUSE::EnvironmentCallFromUMode)
trap_frame.regs->sepc += 4;
if ((to_underlying(scause) & RISCV64::CSR::SCAUSE_INTERRUPT_MASK) != 0) {
// Interrupt
@ -105,7 +110,6 @@ extern "C" void trap_handler(TrapFrame& trap_frame)
}
case EnvironmentCallFromUMode:
trap_frame.regs->sepc += 4;
syscall_handler(&trap_frame);
break;