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risc-v: 0.941
graphic: 0.780
device: 0.675
performance: 0.656
files: 0.642
ppc: 0.545
architecture: 0.508
user-level: 0.423
vnc: 0.406
network: 0.394
semantic: 0.378
socket: 0.365
permissions: 0.306
arm: 0.297
PID: 0.291
boot: 0.281
mistranslation: 0.211
debug: 0.210
peripherals: 0.201
TCG: 0.198
register: 0.191
kernel: 0.183
hypervisor: 0.173
VMM: 0.154
i386: 0.123
KVM: 0.113
virtual: 0.109
x86: 0.098
assembly: 0.081
RISC-V: signal frame is misaligned in signal handlers
Description of problem:
`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.
Steps to 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) {
printf("signal occurred, info: %p, context: %p\n", info, context);
}
int main() {
struct sigaction act;
act.sa_flags = SA_SIGINFO;
act.sa_sigaction = handler;
sigaction(SIGINT, &act, NULL);
// Deliberately misalign the stack
asm volatile ("addi sp, sp, -4");
while(1);
// 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 information:
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.
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