linux-user/s390x: Implement setup_sigtramp

Create and record the two signal trampolines.
Use them when the guest does not use SA_RESTORER.

Cc: qemu-s390x@nongnu.org
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210929130553.121567-22-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/s390x/signal.c

@@ -68,7 +68,6 @@ typedef struct {
     target_sigregs sregs;
     int signo;
     target_sigregs_ext sregs_ext;
-    uint16_t retcode;
 } sigframe;
 
 #define TARGET_UC_VXRS 2
@@ -85,7 +84,6 @@ struct target_ucontext {
 
 typedef struct {
     uint8_t callee_used_stack[__SIGNAL_FRAMESIZE];
-    uint16_t retcode;
     struct target_siginfo info;
     struct target_ucontext uc;
 } rt_sigframe;
@@ -209,9 +207,7 @@ void setup_frame(int sig, struct target_sigaction *ka,
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         restorer = ka->sa_restorer;
     } else {
-        restorer = frame_addr + offsetof(sigframe, retcode);
-        __put_user(S390_SYSCALL_OPCODE | TARGET_NR_sigreturn,
-                   &frame->retcode);
+        restorer = default_sigreturn;
     }
 
     /* Set up registers for signal handler */
@@ -262,9 +258,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         restorer = ka->sa_restorer;
     } else {
-        restorer = frame_addr + offsetof(typeof(*frame), retcode);
-        __put_user(S390_SYSCALL_OPCODE | TARGET_NR_rt_sigreturn,
-                   &frame->retcode);
+        restorer = default_rt_sigreturn;
     }
 
     /* Create siginfo on the signal stack. */
@@ -405,3 +399,17 @@ long do_rt_sigreturn(CPUS390XState *env)
     unlock_user_struct(frame, frame_addr, 0);
     return -TARGET_QEMU_ESIGRETURN;
 }
+
+void setup_sigtramp(abi_ulong sigtramp_page)
+{
+    uint16_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, 2 + 2, 0);
+    assert(tramp != NULL);
+
+    default_sigreturn = sigtramp_page;
+    __put_user(S390_SYSCALL_OPCODE | TARGET_NR_sigreturn, &tramp[0]);
+
+    default_rt_sigreturn = sigtramp_page + 2;
+    __put_user(S390_SYSCALL_OPCODE | TARGET_NR_rt_sigreturn, &tramp[1]);
+
+    unlock_user(tramp, sigtramp_page, 2 + 2);
+}

linux-user/s390x/target_signal.h

@@ -19,4 +19,6 @@ typedef struct target_sigaltstack {
 #include "../generic/signal.h"
 
 #define TARGET_ARCH_HAS_SETUP_FRAME
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1
+
 #endif /* S390X_TARGET_SIGNAL_H */