linux-user: Support for restarting system calls for Alpha targets

Update the Alpha main loop and sigreturn code:
 * on TARGET_ERESTARTSYS, wind guest PC backwards to repeat syscall insn
 * handle TARGET_QEMU_ESIGRETURN in the main loop as the indication
   that the main loop should not touch any guest CPU state
Signed-off-by: NTimothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-13-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
[PMM: tweak commit message; drop TARGET_USE_ERESTARTSYS define;
 PC is env->pc, not env->ir[IR_PV]]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/alpha/target_signal.h

@@ -27,6 +27,7 @@ static inline abi_ulong get_sp_from_cpustate(CPUAlphaState *state)
     return state->ir[IR_SP];
 }
 
+
 /* From <asm/gentrap.h>.  */
 #define TARGET_GEN_INTOVF      -1      /* integer overflow */
 #define TARGET_GEN_INTDIV      -2      /* integer division by zero */

linux-user/main.c

@@ -3267,8 +3267,11 @@ void cpu_loop(CPUAlphaState *env)
                                     env->ir[IR_A2], env->ir[IR_A3],
                                     env->ir[IR_A4], env->ir[IR_A5],
                                     0, 0);
-                if (trapnr == TARGET_NR_sigreturn
-                    || trapnr == TARGET_NR_rt_sigreturn) {
+                if (sysret == -TARGET_ERESTARTSYS) {
+                    env->pc -= 4;
+                    break;
+                }
+                if (sysret == -TARGET_QEMU_ESIGRETURN) {
                     break;
                 }
                 /* Syscall writes 0 to V0 to bypass error check, similar

linux-user/signal.c

@@ -5527,7 +5527,7 @@ long do_sigreturn(CPUAlphaState *env)
 
     restore_sigcontext(env, sc);
     unlock_user_struct(sc, sc_addr, 0);
-    return env->ir[IR_V0];
+    return -TARGET_QEMU_ESIGRETURN;
 
 badframe:
     force_sig(TARGET_SIGSEGV);
@@ -5554,7 +5554,7 @@ long do_rt_sigreturn(CPUAlphaState *env)
     }
 
     unlock_user_struct(frame, frame_addr, 0);
-    return env->ir[IR_V0];
+    return -TARGET_QEMU_ESIGRETURN;
 
 
 badframe: