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)