id = 1093
title = "RISC-V: signal frame is misaligned in signal handlers"
state = "closed"
created_at = "2022-06-29T20:45:51.271Z"
closed_at = "2022-08-02T13:35:56.948Z"
labels = ["Closed::Fixed", "linux-user", "target: riscv"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1093"
host-os = "Linux"
host-arch = "x86_64"
qemu-version = "7.0.0"
guest-os = "n/a"
guest-arch = "RISC-V 64"
description = """`qemu-user` misaligns the signal frame (to 4 bytes rather than 16 bytes) on RISC-V 64, e.g causing pointer misalignment diagnostics to be triggered by UBSan."""
reproduce = """1. Create a C file with the following contents:
```c
#include <signal.h>
#include <stdio.h>

void handler(int sig, siginfo_t *info, void *context) {
\tprintf("signal occurred, info: %p, context: %p\\n", info, context);
}

int main() {
\tstruct sigaction act;
\tact.sa_flags = SA_SIGINFO;
\tact.sa_sigaction = handler;
\tsigaction(SIGINT, &act, NULL);

\t// Deliberately misalign the stack
\tasm volatile ("addi sp, sp, -4");

\twhile(1);
\t// Unreachable
}
```
2. Compile with an appropriate RISC-V toolchain and run with `qemu-riscv64 ./a.out`.
3. Send a `SIGINT` (e.g by hitting Ctrl-C), and observe that the signal frame will be misaligned:
```
signal occurred, info: 0x400080025c, context: 0x40008002dc
```"""
additional = """This issue is alluded to in the source code, see https://gitlab.com/qemu-project/qemu/-/blob/master/linux-user/riscv/signal.c#L68-69. It should be sufficient to change that constant to 15."""