[PATCH v2] tcg: Fix execution on Apple Silicon

[Roman Bolshakov]

Pages can't be both write and executable at the same time on Apple
Silicon. macOS provides public API to switch write protection [1] for
JIT applications, like TCG.

1. 
https://developer.apple.com/documentation/apple_silicon/porting_just-in-time_compilers_to_apple_silicon

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
---
v1: https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg00073.html
Changes since v1:

 - Pruned not needed fiddling with W^X and dropped symmetry from write
   lock/unlock and renamed related functions.
   Similar approach is used in JavaScriptCore [1].

 - Moved jit helper functions to util/osdep
                                                                                
                                                                  As outlined 
in osdep.h, this matches to (2):                                                
                                                                                
                                                                                
                                    * In an ideal world this header would 
contain only:                                                                   
                         *  (1) things which everybody needs                    
                                                                                
        *  (2) things without which code would work on most platforms but       
                                                                       *      
fail to compile or misbehave on a minority of host OSes

 - Fixed a checkpatch error

 - Limit new behaviour only to macOS 11.0 and above, because of the
   following declarations:

   __API_AVAILABLE(macos(11.0))
   __API_UNAVAILABLE(ios, tvos, watchos)
   void pthread_jit_write_protect_np(int enabled);

   __API_AVAILABLE(macos(11.0))
   __API_UNAVAILABLE(ios, tvos, watchos)
   int pthread_jit_write_protect_supported_np(void);

 1. https://bugs.webkit.org/attachment.cgi?id=402515&action=prettypatch

 accel/tcg/cpu-exec.c      |  2 ++
 accel/tcg/translate-all.c |  6 ++++++
 include/qemu/osdep.h      |  3 +++
 tcg/tcg.c                 |  1 +
 util/osdep.c              | 22 ++++++++++++++++++++++
 5 files changed, 34 insertions(+)

diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 8689c54499..374060eb45 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -175,6 +175,7 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, 
TranslationBlock *itb)
     }
 #endif /* DEBUG_DISAS */
 
+    qemu_thread_jit_execute();
     ret = tcg_qemu_tb_exec(env, tb_ptr);
     cpu->can_do_io = 1;
     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
@@ -382,6 +383,7 @@ static inline void tb_add_jump(TranslationBlock *tb, int n,
 {
     uintptr_t old;
 
+    qemu_thread_jit_write();
     assert(n < ARRAY_SIZE(tb->jmp_list_next));
     qemu_spin_lock(&tb_next->jmp_lock);
 
diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index b7d50a73d4..88ae5d35ef 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -1072,6 +1072,9 @@ static inline void *alloc_code_gen_buffer(void)
     size_t size = tcg_ctx->code_gen_buffer_size;
     void *buf;
 
+#if defined(__APPLE__) && defined(MAC_OS_VERSION_11_0)
+    flags |= MAP_JIT;
+#endif
     buf = mmap(NULL, size, prot, flags, -1, 0);
     if (buf == MAP_FAILED) {
         return NULL;
@@ -1485,7 +1488,9 @@ static void do_tb_phys_invalidate(TranslationBlock *tb, 
bool rm_from_page_list)
 
 static void tb_phys_invalidate__locked(TranslationBlock *tb)
 {
+    qemu_thread_jit_write();
     do_tb_phys_invalidate(tb, true);
+    qemu_thread_jit_execute();
 }
 
 /* invalidate one TB
@@ -1687,6 +1692,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
 #endif
 
     assert_memory_lock();
+    qemu_thread_jit_write();
 
     phys_pc = get_page_addr_code(env, pc);
 
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index f9ec8c84e9..89abebcf5d 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -686,4 +686,7 @@ char *qemu_get_host_name(Error **errp);
  */
 size_t qemu_get_host_physmem(void);
 
+void qemu_thread_jit_write(void);
+void qemu_thread_jit_execute(void);
+
 #endif
diff --git a/tcg/tcg.c b/tcg/tcg.c
index 43c6cf8f52..ab8488f5d5 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1065,6 +1065,7 @@ void tcg_prologue_init(TCGContext *s)
     s->pool_labels = NULL;
 #endif
 
+    qemu_thread_jit_write();
     /* Generate the prologue.  */
     tcg_target_qemu_prologue(s);
 
diff --git a/util/osdep.c b/util/osdep.c
index 66d01b9160..80ec7185da 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -606,3 +606,25 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
     return readv_writev(fd, iov, iov_cnt, true);
 }
 #endif
+
+#if defined(__APPLE__) && defined(MAC_OS_VERSION_11_0)
+static inline void qemu_thread_jit_write_protect(bool enabled)
+{
+    if (pthread_jit_write_protect_supported_np()) {
+        pthread_jit_write_protect_np(enabled);
+    }
+}
+
+void qemu_thread_jit_execute(void)
+{
+    qemu_thread_jit_write_protect(true);
+}
+
+void qemu_thread_jit_write(void)
+{
+    qemu_thread_jit_write_protect(false);
+}
+#else
+void qemu_thread_jit_write(void) {}
+void qemu_thread_jit_execute(void) {}
+#endif
-- 
2.29.2