linux-user: Add cpu_loop_exit_sigsegv

This is a new interface to be provided by the os emulator for
raising SIGSEGV on fault.  Use the new record_sigsegv target hook.

Reviewed by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/user-exec.c

@@ -141,35 +141,38 @@ static int probe_access_internal(CPUArchState *env, target_ulong addr,
                                  int fault_size, MMUAccessType access_type,
                                  bool nonfault, uintptr_t ra)
 {
-    int flags;
+    int acc_flag;
+    bool maperr;
 
     switch (access_type) {
     case MMU_DATA_STORE:
-        flags = PAGE_WRITE;
+        acc_flag = PAGE_WRITE_ORG;
         break;
     case MMU_DATA_LOAD:
-        flags = PAGE_READ;
+        acc_flag = PAGE_READ;
         break;
     case MMU_INST_FETCH:
-        flags = PAGE_EXEC;
+        acc_flag = PAGE_EXEC;
         break;
     default:
         g_assert_not_reached();
     }
 
-    if (!guest_addr_valid_untagged(addr) ||
-        page_check_range(addr, 1, flags) < 0) {
-        if (nonfault) {
-            return TLB_INVALID_MASK;
-        } else {
-            CPUState *cpu = env_cpu(env);
-            CPUClass *cc = CPU_GET_CLASS(cpu);
-            cc->tcg_ops->tlb_fill(cpu, addr, fault_size, access_type,
-                                  MMU_USER_IDX, false, ra);
-            g_assert_not_reached();
+    if (guest_addr_valid_untagged(addr)) {
+        int page_flags = page_get_flags(addr);
+        if (page_flags & acc_flag) {
+            return 0; /* success */
         }
+        maperr = !(page_flags & PAGE_VALID);
+    } else {
+        maperr = true;
+    }
+
+    if (nonfault) {
+        return TLB_INVALID_MASK;
     }
-    return 0;
+
+    cpu_loop_exit_sigsegv(env_cpu(env), addr, access_type, maperr, ra);
 }
 
 int probe_access_flags(CPUArchState *env, target_ulong addr,

include/exec/exec-all.h

@@ -685,6 +685,21 @@ MMUAccessType adjust_signal_pc(uintptr_t *pc, bool is_write);
 bool handle_sigsegv_accerr_write(CPUState *cpu, sigset_t *old_set,
                                  uintptr_t host_pc, abi_ptr guest_addr);
 
+/**
+ * cpu_loop_exit_sigsegv:
+ * @cpu: the cpu context
+ * @addr: the guest address of the fault
+ * @access_type: access was read/write/execute
+ * @maperr: true for invalid page, false for permission fault
+ * @ra: host pc for unwinding
+ *
+ * Use the TCGCPUOps hook to record cpu state, do guest operating system
+ * specific things to raise SIGSEGV, and jump to the main cpu loop.
+ */
+void QEMU_NORETURN cpu_loop_exit_sigsegv(CPUState *cpu, target_ulong addr,
+                                         MMUAccessType access_type,
+                                         bool maperr, uintptr_t ra);
+
 #else
 static inline void mmap_lock(void) {}
 static inline void mmap_unlock(void) {}

linux-user/signal.c

@@ -688,9 +688,27 @@ void force_sigsegv(int oldsig)
     }
     force_sig(TARGET_SIGSEGV);
 }
-
 #endif
 
+void cpu_loop_exit_sigsegv(CPUState *cpu, target_ulong addr,
+                           MMUAccessType access_type, bool maperr, uintptr_t ra)
+{
+    const struct TCGCPUOps *tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
+
+    if (tcg_ops->record_sigsegv) {
+        tcg_ops->record_sigsegv(cpu, addr, access_type, maperr, ra);
+    } else if (tcg_ops->tlb_fill) {
+        tcg_ops->tlb_fill(cpu, addr, 0, access_type, MMU_USER_IDX, false, ra);
+        g_assert_not_reached();
+    }
+
+    force_sig_fault(TARGET_SIGSEGV,
+                    maperr ? TARGET_SEGV_MAPERR : TARGET_SEGV_ACCERR,
+                    addr);
+    cpu->exception_index = EXCP_INTERRUPT;
+    cpu_loop_exit_restore(cpu, ra);
+}
+
 /* abort execution with signal */
 static void QEMU_NORETURN dump_core_and_abort(int target_sig)
 {
@@ -806,7 +824,7 @@ static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
         access_type = adjust_signal_pc(&pc, is_write);
 
         if (host_sig == SIGSEGV) {
-            const struct TCGCPUOps *tcg_ops;
+            bool maperr = true;
 
             if (info->si_code == SEGV_ACCERR && h2g_valid(host_addr)) {
                 /* If this was a write to a TB protected page, restart. */
@@ -821,18 +839,14 @@ static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
                  * which means that we may get ACCERR when we want MAPERR.
                  */
                 if (page_get_flags(guest_addr) & PAGE_VALID) {
-                    /* maperr = false; */
+                    maperr = false;
                 } else {
                     info->si_code = SEGV_MAPERR;
                 }
             }
 
             sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
-
-            tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
-            tcg_ops->tlb_fill(cpu, guest_addr, 0, access_type,
-                              MMU_USER_IDX, false, pc);
-            g_assert_not_reached();
+            cpu_loop_exit_sigsegv(cpu, guest_addr, access_type, maperr, pc);
         } else {
             sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
         }