there is no output.through my effort, I find mret exception happens
The issue turned out to be RISC-V's Physical Memory Protection (PMP). QEMU will raise an illegal instruction exception when executing an MRET instruction if no PMP rules have been defined. Adding a PMP entry resolved the issue.
so ,I add setup_pmp function in kernel/start.c
`
void setup_pmp(void)
{
// Set up a PMP to permit access to all of memory.
// Ignore the illegal-instruction trap if PMPs aren't supported.
unsigned long pmpc = PMP_NAPOT | PMP_R | PMP_W | PMP_X;
asm volatile ("la t0, 1f\n\t"
"csrrw t0, mtvec, t0\n\t"
"csrw pmpaddr0, %1\n\t"
"csrw pmpcfg0, %0\n\t"
".align 2\n\t"
"1: csrw mtvec, t0"
: : "r" (pmpc), "r" (-1UL) : "t0");
}
// entry.S jumps here in machine mode on stack0.
void
start()
{
setup_pmp();
........
}
qemu-system-riscv64 --version QEMU emulator version 6.1.0 Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developers
make kernel/kernel qemu-system-riscv64 -M virt -kernel kernel/kernel -bios none -serial stdio -display none
there is no output.through my effort, I find mret exception happens
The issue turned out to be RISC-V's Physical Memory Protection (PMP). QEMU will raise an illegal instruction exception when executing an MRET instruction if no PMP rules have been defined. Adding a PMP entry resolved the issue.
so ,I add setup_pmp function in kernel/start.c
` void setup_pmp(void) { // Set up a PMP to permit access to all of memory. // Ignore the illegal-instruction trap if PMPs aren't supported. unsigned long pmpc = PMP_NAPOT | PMP_R | PMP_W | PMP_X; asm volatile ("la t0, 1f\n\t" "csrrw t0, mtvec, t0\n\t" "csrw pmpaddr0, %1\n\t" "csrw pmpcfg0, %0\n\t" ".align 2\n\t" "1: csrw mtvec, t0" : : "r" (pmpc), "r" (-1UL) : "t0"); }
// entry.S jumps here in machine mode on stack0. void start() { setup_pmp(); ........ }
`