[Qemu-devel] [PATCH 2/5] user-exec: Push resume-from-signal code out to handle_cpu_signal()

[Peter Maydell]

Since the only caller of page_unprotect() which might cause it to
need to call cpu_resume_from_signal() is handle_cpu_signal() in
the user-mode code, push the longjump handling out to that function.

Since this is the only caller of cpu_resume_from_signal() which
passes a non-NULL puc argument, split the non-NULL handling into
a new cpu_exit_tb_from_sighandler() function. This allows us
to merge the softmmu and usermode implementations of the
cpu_resume_from_signal() function, which are now identical.

Signed-off-by: Peter Maydell <address@hidden>
---
 cpu-exec-common.c |  2 +-
 translate-all.c   | 12 ++++++++----
 translate-all.h   |  2 +-
 user-exec.c       | 41 +++++++++++++++++++++++++++++------------
 4 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/cpu-exec-common.c b/cpu-exec-common.c
index 6bdda6b..62f5d6b 100644
--- a/cpu-exec-common.c
+++ b/cpu-exec-common.c
@@ -28,7 +28,6 @@ CPUState *tcg_current_cpu;
 /* exit the current TB from a signal handler. The host registers are
    restored in a state compatible with the CPU emulator
  */
-#if defined(CONFIG_SOFTMMU)
 void cpu_resume_from_signal(CPUState *cpu, void *puc)
 {
     /* XXX: restore cpu registers saved in host registers */
@@ -37,6 +36,7 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
     siglongjmp(cpu->jmp_env, 1);
 }
 
+#if defined(CONFIG_SOFTMMU)
 void cpu_reloading_memory_map(void)
 {
     if (qemu_in_vcpu_thread()) {
diff --git a/translate-all.c b/translate-all.c
index 4820d2e..52a571e 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -1955,7 +1955,7 @@ int page_check_range(target_ulong start, target_ulong 
len, int flags)
             /* unprotect the page if it was put read-only because it
                contains translated code */
             if (!(p->flags & PAGE_WRITE)) {
-                if (!page_unprotect(addr, 0, NULL)) {
+                if (!page_unprotect(addr, 0)) {
                     return -1;
                 }
             }
@@ -1965,8 +1965,12 @@ int page_check_range(target_ulong start, target_ulong 
len, int flags)
 }
 
 /* called from signal handler: invalidate the code and unprotect the
-   page. Return TRUE if the fault was successfully handled. */
-int page_unprotect(target_ulong address, uintptr_t pc, void *puc)
+ * page. Return 0 if the fault was not handled, 1 if it was handled,
+ * and 2 if it was handled but the caller must cause the TB to be
+ * immediately exited. (We can only return 2 if the 'pc' argument is
+ * non-zero.)
+ */
+int page_unprotect(target_ulong address, uintptr_t pc)
 {
     unsigned int prot;
     PageDesc *p;
@@ -1999,7 +2003,7 @@ int page_unprotect(target_ulong address, uintptr_t pc, 
void *puc)
                the corresponding translated code. */
             if (tb_invalidate_phys_page(addr, pc)) {
                 mmap_unlock();
-                cpu_resume_from_signal(current_cpu, puc);
+                return 2;
             }
 #ifdef DEBUG_TB_CHECK
             tb_invalidate_check(addr);
diff --git a/translate-all.h b/translate-all.h
index 0384640..ce6071b 100644
--- a/translate-all.h
+++ b/translate-all.h
@@ -27,7 +27,7 @@ void tb_invalidate_phys_range(tb_page_addr_t start, 
tb_page_addr_t end);
 void tb_check_watchpoint(CPUState *cpu);
 
 #ifdef CONFIG_USER_ONLY
-int page_unprotect(target_ulong address, uintptr_t pc, void *puc);
+int page_unprotect(target_ulong address, uintptr_t pc);
 #endif
 
 #endif /* TRANSLATE_ALL_H */
diff --git a/user-exec.c b/user-exec.c
index d8d597b..1d02e24 100644
--- a/user-exec.c
+++ b/user-exec.c
@@ -54,7 +54,7 @@ static void exception_action(CPUState *cpu)
 /* exit the current TB from a signal handler. The host registers are
    restored in a state compatible with the CPU emulator
  */
-void cpu_resume_from_signal(CPUState *cpu, void *puc)
+static void cpu_exit_tb_from_sighandler(CPUState *cpu, void *puc)
 {
 #ifdef __linux__
     struct ucontext *uc = puc;
@@ -62,20 +62,18 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
     struct sigcontext *uc = puc;
 #endif
 
-    if (puc) {
-        /* XXX: use siglongjmp ? */
+    /* XXX: use siglongjmp ? */
 #ifdef __linux__
 #ifdef __ia64
-        sigprocmask(SIG_SETMASK, (sigset_t *)&uc->uc_sigmask, NULL);
+    sigprocmask(SIG_SETMASK, (sigset_t *)&uc->uc_sigmask, NULL);
 #else
-        sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+    sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
 #endif
 #elif defined(__OpenBSD__)
-        sigprocmask(SIG_SETMASK, &uc->sc_mask, NULL);
+    sigprocmask(SIG_SETMASK, &uc->sc_mask, NULL);
 #endif
-    }
-    cpu->exception_index = -1;
-    siglongjmp(cpu->jmp_env, 1);
+
+    cpu_resume_from_signal(cpu, NULL);
 }
 
 /* 'pc' is the host PC at which the exception was raised. 'address' is
@@ -95,9 +93,28 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned 
long address,
            pc, address, is_write, *(unsigned long *)old_set);
 #endif
     /* XXX: locking issue */
-    if (is_write && h2g_valid(address)
-        && page_unprotect(h2g(address), pc, puc)) {
-        return 1;
+    if (is_write && h2g_valid(address)) {
+        switch (page_unprotect(h2g(address), pc)) {
+        case 0:
+            /* Fault not caused by a page marked unwritable to protect
+             * cached translations, must be the guest binary's problem
+             */
+            break;
+        case 1:
+            /* Fault caused by protection of cached translation; TBs
+             * invalidated, so resume execution
+             */
+            return 1;
+        case 2:
+            /* Fault caused by protection of cached translation, and the
+             * currently executing TB was modified and must be exited
+             * immediately.
+             */
+            cpu_exit_tb_from_sighandler(current_cpu, puc);
+            g_assert_not_reached();
+        default:
+            g_assert_not_reached();
+        }
     }
 
     /* Convert forcefully to guest address space, invalid addresses
-- 
1.9.1