No longer need SPRR and probe it runtime

Author: wtdcode

qemu/accel/tcg/translate-all.c

@@ -2172,21 +2172,19 @@ void tcg_flush_softmmu_tlb(struct uc_struct *uc)
 }
 
 
-#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) && defined(HAVE_SPRR) && (defined(__arm__) || defined(__aarch64__))
+#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) && (defined(__arm__) || defined(__aarch64__))
 static bool tb_exec_is_locked(struct uc_struct *uc)
 {
     return uc->current_executable;
 }
 
 static void tb_exec_change(struct uc_struct *uc, bool executable)
 {
-    assert(uc->current_executable == thread_executable());
+    assert_executable(uc->current_executable);
     if (uc->current_executable != executable) {
         jit_write_protect(executable);
         uc->current_executable = executable;
-        assert(
-            executable == thread_executable()
-        );
+        assert_executable(executable);
     }
 }
 #else /* not needed on non-Darwin platforms */

qemu/configure

@@ -2155,11 +2155,17 @@ int main() {
 
     // In Apple Hypervisor, this value is not accessbile and
     // pthread_jit_write_protect_np essentially is a no-op
+    
+    /*
     if (!commpage_sprr) {
         return 1;
     } else {
         return 0;
     }
+    */
+
+    // Now it is accessible but always zero, let's probe it runtime.
+    return 0;
 }
 EOF
     if ! compile_prog ""; then
@@ -2171,7 +2177,6 @@ EOF
         have_sprr='yes'
       else
         have_sprr='no'
-        have_pthread_jit_protect='no'
       fi
     fi
   fi

qemu/include/tcg/tcg-apple-jit.h

@@ -25,18 +25,18 @@
 #ifndef TCG_APPLE_JIT_H
 #define TCG_APPLE_JIT_H
 
-#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) && defined(HAVE_SPRR) && (defined(__arm__) || defined(__aarch64__))
+#include "assert.h"
+#include "stdint.h"
+#include "stdlib.h"
+#include "stdbool.h"
 
-/* write protect enable = write disable */
-static inline void jit_write_protect(int enabled)
-{
-    return pthread_jit_write_protect_np(enabled);
-}
+#if defined(__APPLE__) && defined(HAVE_SPRR) && (defined(__arm__) || defined(__aarch64__))
 
 // Returns the S3_6_c15_c1_5 register's value
 // Taken from 
 // https://stackoverflow.com/questions/70019553/lldb-how-to-read-the-permissions-of-a-memory-region-for-a-thread
 // https://blog.svenpeter.dev/posts/m1_sprr_gxf/
+// On Github Action (Virtualized environment), this shall always returns 0
 static inline uint64_t read_sprr_perm(void)
 {
     uint64_t v;
@@ -50,7 +50,11 @@ __attribute__((unused)) static inline uint8_t thread_mask()
 {
     uint64_t v = read_sprr_perm();
 
-    return (v >> 20) & 3;
+    if (v == 0) {
+        return 0;
+    } else {
+        return (v >> 20) & 3;
+    }
 }
 
 __attribute__((unused)) static inline bool thread_writeable()
@@ -63,25 +67,69 @@ __attribute__((unused)) static inline bool thread_executable()
     return thread_mask() == 1;
 }
 
+static inline void assert_executable(bool executable) {
+    uint64_t v = read_sprr_perm();
+
+    if (!v) {
+        assert(executable == thread_executable());
+    }
+}
+
+#else
+
+// Returns the S3_6_c15_c1_5 register's value
+// Taken from 
+// https://stackoverflow.com/questions/70019553/lldb-how-to-read-the-permissions-of-a-memory-region-for-a-thread
+// https://blog.svenpeter.dev/posts/m1_sprr_gxf/
+static inline uint64_t read_sprr_perm(void)
+{
+    return 0;
+}
+
+__attribute__((unused)) static inline uint8_t thread_mask() 
+{
+    return 0;
+}
+
+__attribute__((unused)) static inline bool thread_writeable()
+{
+    return false;
+}
+
+__attribute__((unused)) static inline bool thread_executable()
+{
+    return false;
+}
+
+static inline void assert_executable(bool executable) {
+}
+
+#endif
+
+
+#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) && defined(HAVE_SPRR) && (defined(__arm__) || defined(__aarch64__))
+
+/* write protect enable = write disable */
+static inline void jit_write_protect(int enabled)
+{
+    return pthread_jit_write_protect_np(enabled);
+}
+
 #define JIT_CALLBACK_GUARD(x)                       \
 {                                                   \
     bool executable = uc->current_executable;       \
-    assert (executable == thread_executable());     \
+    assert_executable(executable);                  \
     x;                                              \
-    if (executable != thread_executable()) {        \
-        jit_write_protect(executable);              \
-    }                                               \
+    jit_write_protect(executable);                  \
 }                                                   \
 
 
 #define JIT_CALLBACK_GUARD_VAR(var, x)                  \
 {                                                       \
     bool executable = uc->current_executable;           \
-    assert (executable == thread_executable());         \
+    assert_executable(executable);                      \
     var = x;                                            \
-    if (executable != thread_executable()) {            \
-        jit_write_protect(executable);                  \
-    }                                                   \
+    jit_write_protect(executable);                      \
 }                                                       \
 
 

uc.c

@@ -35,8 +35,7 @@ static void clear_deleted_hooks(uc_engine *uc);
 static uc_err uc_snapshot(uc_engine *uc);
 static uc_err uc_restore_latest_snapshot(uc_engine *uc);
 
-#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) &&                 \
-    defined(HAVE_SPRR) && (defined(__arm__) || defined(__aarch64__))
+#if defined(__APPLE__) && defined(HAVE_PTHREAD_JIT_PROTECT) && (defined(__arm__) || defined(__aarch64__))
 static void save_jit_state(uc_engine *uc)
 {
     if (!uc->nested) {
@@ -51,7 +50,7 @@ static void restore_jit_state(uc_engine *uc)
 {
     assert(uc->nested > 0);
     if (uc->nested == 1) {
-        assert(uc->current_executable == thread_executable());
+        assert_executable(uc->current_executable);
         if (uc->current_executable != uc->thread_executable_entry) {
             if (uc->thread_executable_entry) {
                 jit_write_protect(true);