linux-user: Support for restarting system calls for x86 targets

Update the x86 main loop and sigreturn code:
 * on TARGET_ERESTARTSYS, wind guest PC backwards to repeat syscall insn
 * set all guest CPU state within signal.c code rather than passing it
   back out as the "return code" from do_sigreturn()
 * handle TARGET_QEMU_ESIGRETURN in the main loop as the indication
   that the main loop should not touch EAX

Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-5-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: Commit message tweaks; drop TARGET_USE_ERESTARTSYS define]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

3 files changed, 36 insertions, 28 deletions

diff --git a/linux-user/main.c b/linux-user/main.c
index 95ed11d85c..da5a0333b6 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -285,6 +285,7 @@ void cpu_loop(CPUX86State *env)
     CPUState *cs = CPU(x86_env_get_cpu(env));
     int trapnr;
     abi_ulong pc;
+    abi_ulong ret;
     target_siginfo_t info;
 
     for(;;) {
@@ -294,28 +295,38 @@ void cpu_loop(CPUX86State *env)
         switch(trapnr) {
         case 0x80:
             /* linux syscall from int $0x80 */
-            env->regs[R_EAX] = do_syscall(env,
-                                          env->regs[R_EAX],
-                                          env->regs[R_EBX],
-                                          env->regs[R_ECX],
-                                          env->regs[R_EDX],
-                                          env->regs[R_ESI],
-                                          env->regs[R_EDI],
-                                          env->regs[R_EBP],
-                                          0, 0);
+            ret = do_syscall(env,
+                             env->regs[R_EAX],
+                             env->regs[R_EBX],
+                             env->regs[R_ECX],
+                             env->regs[R_EDX],
+                             env->regs[R_ESI],
+                             env->regs[R_EDI],
+                             env->regs[R_EBP],
+                             0, 0);
+            if (ret == -TARGET_ERESTARTSYS) {
+                env->eip -= 2;
+            } else if (ret != -TARGET_QEMU_ESIGRETURN) {
+                env->regs[R_EAX] = ret;
+            }
             break;
 #ifndef TARGET_ABI32
         case EXCP_SYSCALL:
             /* linux syscall from syscall instruction */
-            env->regs[R_EAX] = do_syscall(env,
-                                          env->regs[R_EAX],
-                                          env->regs[R_EDI],
-                                          env->regs[R_ESI],
-                                          env->regs[R_EDX],
-                                          env->regs[10],
-                                          env->regs[8],
-                                          env->regs[9],
-                                          0, 0);
+            ret = do_syscall(env,
+                             env->regs[R_EAX],
+                             env->regs[R_EDI],
+                             env->regs[R_ESI],
+                             env->regs[R_EDX],
+                             env->regs[10],
+                             env->regs[8],
+                             env->regs[9],
+                             0, 0);
+            if (ret == -TARGET_ERESTARTSYS) {
+                env->eip -= 2;
+            } else if (ret != -TARGET_QEMU_ESIGRETURN) {
+                env->regs[R_EAX] = ret;
+            }
             break;
 #endif
         case EXCP0B_NOSEG:
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 04c21d0ccd..11ddd05173 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -1024,7 +1024,7 @@ give_sigsegv:
 }
 
 static int
-restore_sigcontext(CPUX86State *env, struct target_sigcontext *sc, int *peax)
+restore_sigcontext(CPUX86State *env, struct target_sigcontext *sc)
 {
     unsigned int err = 0;
     abi_ulong fpstate_addr;
@@ -1042,6 +1042,7 @@ restore_sigcontext(CPUX86State *env, struct target_sigcontext *sc, int *peax)
     env->regs[R_EBX] = tswapl(sc->ebx);
     env->regs[R_EDX] = tswapl(sc->edx);
     env->regs[R_ECX] = tswapl(sc->ecx);
+    env->regs[R_EAX] = tswapl(sc->eax);
     env->eip = tswapl(sc->eip);
 
     cpu_x86_load_seg(env, R_CS, lduw_p(&sc->cs) | 3);
@@ -1059,7 +1060,6 @@ restore_sigcontext(CPUX86State *env, struct target_sigcontext *sc, int *peax)
         cpu_x86_frstor(env, fpstate_addr, 1);
     }
 
-    *peax = tswapl(sc->eax);
     return err;
 badframe:
     return 1;
@@ -1071,7 +1071,7 @@ long do_sigreturn(CPUX86State *env)
     abi_ulong frame_addr = env->regs[R_ESP] - 8;
     target_sigset_t target_set;
     sigset_t set;
-    int eax, i;
+    int i;
 
     trace_user_do_sigreturn(env, frame_addr);
     if (!lock_user_struct(VERIFY_READ, frame, frame_addr, 1))
@@ -1086,10 +1086,10 @@ long do_sigreturn(CPUX86State *env)
     do_sigprocmask(SIG_SETMASK, &set, NULL);
 
     /* restore registers */
-    if (restore_sigcontext(env, &frame->sc, &eax))
+    if (restore_sigcontext(env, &frame->sc))
         goto badframe;
     unlock_user_struct(frame, frame_addr, 0);
-    return eax;
+    return -TARGET_QEMU_ESIGRETURN;
 
 badframe:
     unlock_user_struct(frame, frame_addr, 0);
@@ -1102,7 +1102,6 @@ long do_rt_sigreturn(CPUX86State *env)
     abi_ulong frame_addr;
     struct rt_sigframe *frame;
     sigset_t set;
-    int eax;
 
     frame_addr = env->regs[R_ESP] - 4;
     trace_user_do_rt_sigreturn(env, frame_addr);
@@ -1111,7 +1110,7 @@ long do_rt_sigreturn(CPUX86State *env)
     target_to_host_sigset(&set, &frame->uc.tuc_sigmask);
     do_sigprocmask(SIG_SETMASK, &set, NULL);
 
-    if (restore_sigcontext(env, &frame->uc.tuc_mcontext, &eax)) {
+    if (restore_sigcontext(env, &frame->uc.tuc_mcontext)) {
         goto badframe;
     }
 
@@ -1121,7 +1120,7 @@ long do_rt_sigreturn(CPUX86State *env)
     }
 
     unlock_user_struct(frame, frame_addr, 0);
-    return eax;
+    return -TARGET_QEMU_ESIGRETURN;
 
 badframe:
     unlock_user_struct(frame, frame_addr, 0);
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index f4c2e190f8..a4a1af75f6 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6940,12 +6940,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         break;
 #ifdef TARGET_NR_sigreturn
     case TARGET_NR_sigreturn:
-        /* NOTE: ret is eax, so not transcoding must be done */
         ret = do_sigreturn(cpu_env);
         break;
 #endif
     case TARGET_NR_rt_sigreturn:
-        /* NOTE: ret is eax, so not transcoding must be done */
         ret = do_rt_sigreturn(cpu_env);
         break;
     case TARGET_NR_sethostname: