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Re: [PATCH] linux-user/riscv: fix up struct target_ucontext definition

From: LIU Zhiwei
Subject: Re: [PATCH] linux-user/riscv: fix up struct target_ucontext definition
Date: Wed, 22 Apr 2020 10:34:11 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0


When I port RISU, I find this bug. I can't get the correct registers from the
struct ucontext_t parameter in the signal handler.

If you want to reproduce it, just   register a signal handler for SIGILL,
and  output an illegal instruction, such as
#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <string.h>
#include <signal.h>
#include <ucontext.h>

void sigill(int sig, siginfo_t *si, void *uc)
    printf("Illegal pc: %016" PRIx64 "\n",
           ((ucontext_t *)uc)->uc_mcontext.__gregs[0]);

static void set_sigill_handler(void (*fn) (int, siginfo_t *, void *))
    struct sigaction sa;
    memset(&sa, 0, sizeof(struct sigaction));

    sa.sa_sigaction = fn;
    sa.sa_flags = SA_SIGINFO;
    if (sigaction(SIGILL, &sa, 0) != 0) {

int main()
    asm(".dword 0x0000006b");
    return 0;

On 2020/4/12 10:08, LIU Zhiwei wrote:
As struct target_ucontext will be transfered to signal handler, it
must keep pace with struct ucontext_t defined in Linux kernel.

Signed-off-by: LIU Zhiwei <address@hidden>
 linux-user/riscv/signal.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/linux-user/riscv/signal.c b/linux-user/riscv/signal.c
index 83ecc6f799..67a95dbc7b 100644
--- a/linux-user/riscv/signal.c
+++ b/linux-user/riscv/signal.c
@@ -40,8 +40,9 @@ struct target_ucontext {
     unsigned long uc_flags;
     struct target_ucontext *uc_link;
     target_stack_t uc_stack;
-    struct target_sigcontext uc_mcontext;
     target_sigset_t uc_sigmask;
+    uint8_t   __unused[1024 / 8 - sizeof(target_sigset_t)];
+    struct target_sigcontext uc_mcontext QEMU_ALIGNED(16);
 struct target_rt_sigframe {

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