ENJOU1224 opened a new pull request, #17767:
URL: https://github.com/apache/nuttx/pull/17767
## Summary
This PR fixes a runtime crash on QEMU `rv-virt` when the RISC-V Vector
extension is enabled.
The `riscv_vpuconfig()` function, responsible for initializing the
`mstatus.VS` bit (Vector Status), was defined but never called during the
board-specific startup in `qemu_rv_start()` for the `rv-virt` platform. This
oversight caused `mstatus.VS` to remain in the `Off` state (0x00), leading to
an `Illegal Instruction` exception (MCAUSE: 0x2) when the OS attempted to save
or restore vector context .
This patch adds the necessary call to `riscv_vpuconfig()` in
`arch/risc-v/src/qemu-rv/qemu_rv_start.c`, ensuring the VPU is correctly
initialized on boot.
## Impact
* **Is new feature added?** No.
* **Is existing feature changed?** Yes. Fixes broken Vector extension
support on QEMU.
* **Impact on user:** Users enabling RISC-V Vector extensions on QEMU
(`rv-virt`) can now compile and boot successfully without runtime crashes.
Users not enabling Vector extensions are unaffected.
* **Impact on build:** No direct impact on the build process.
* **Impact on hardware:** Validated on QEMU RISC-V 32-bit. No changes to
physical hardware are implied.
* **Impact on documentation:** No.
* **Impact on security:** No.
* **Impact on compatibility:** This fix addresses a pre-existing runtime
failure. It improves compatibility for systems configured with RISC-V Vector
extensions.
## Testing
**Host Environment:**
* **OS:** Ubuntu 25.10 (Linux 6.17.0-8-generic)
* **Compiler:** riscv64-unknown-elf-gcc (14.2.0+19) 14.2.0
* **QEMU:** QEMU emulator version 10.1.50 (v10.1.0-1314-gf3f2ad1193)
**Verification Steps:**
1. **Build Verification:**
* **Target:** `rv-virt:nsh` (Configured with `CONFIG_ARCH_RV_ISA_V=y`).
* **Command:** `make -j`
* **Result:** Build completes successfully (provided that prerequisite
type-fixing patch PR #17762 is applied).
2. **Runtime Verification:**
* **Command:**
```bash
qemu-system-riscv32 \
-nographic \
-M virt \
-bios none \
-kernel ./nuttx \
-cpu max,vlen=256,elen=64
```
* **Before check:** System boots to NSH, but after executing a few NSH
commands (typically within 2-3 commands) crashes with:
```text
riscv_exception: EXCEPTION: Illegal instruction. MCAUSE: 00000002,
EPC: 80000xxx, MTVAL: 0c3073d7 # vsetvli instruction
```
This occurs because `mstatus.VS` is not correctly initialized,
preventing vector instructions from executing.
* **After check:** System boots to NSH and runs stably, allowing
execution of NSH commands (e.g., `ls`, `ps`). The `Illegal Instruction`
exception is no longer observed.
**Boot Log (After Fix):**
```text
ABC
NuttShell (NSH) NuttX-12.12.0
nsh> ls
/:
dev/
proc/
nsh> ps
TID PID PPID PRI POLICY TYPE NPX STATE EVENT SIGMASK
STACK USED FILLED COMMAND
0 0 0 0 FIFO Kthread - Ready
0000000000000000 0002032 0000420 20.6% Idle_Task
1 1 0 100 RR Task - Running
0000000000000000 0002000 0001636 81.8%! nsh_main
nsh>
``````
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