linux-user/x86_64: Raise SIGSEGV if SA_RESTORER not set

This has been a fixme for some time.  The effect of
returning -EFAULT from the kernel code is to raise SIGSEGV.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210929130553.121567-12-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/i386/signal.c

@@ -421,19 +421,18 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
 
     /* Set up to return from userspace.  If provided, use a stub
        already in userspace.  */
-#ifndef TARGET_X86_64
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         __put_user(ka->sa_restorer, &frame->pretcode);
     } else {
+#ifdef TARGET_X86_64
+        /* For x86_64, SA_RESTORER is required ABI.  */
+        goto give_sigsegv;
+#else
         /* This is no longer used, but is retained for ABI compatibility. */
         install_rt_sigtramp(frame->retcode);
         __put_user(default_rt_sigreturn, &frame->pretcode);
-    }
-#else
-    /* XXX: Would be slightly better to return -EFAULT here if test fails
-       assert(ka->sa_flags & TARGET_SA_RESTORER); */
-    __put_user(ka->sa_restorer, &frame->pretcode);
 #endif
+    }
 
     /* Set up registers for signal handler */
     env->regs[R_ESP] = frame_addr;