[Qemu-devel] [PATCH v4 04/10] tcg: Init TB's direct jumps before making it visible

[Sergey Fedorov <sergey.fedorov@linaro.org>]

From: Sergey Fedorov <serge.fdrv@gmail.com>

Initialize TB's direct jump list data fields and reset the jumps before
tb_link_page() puts it into the physical hash table and the physical
page list. So TB is completely initialized before it becomes visible.

This is pure rearrangement of code to a more suitable place, though it
could be a preparation for relaxing the locking scheme in future.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
---

Changes in v4:
 * Added comment on TB stuff synchronization
 * Expanded commit message
Changes in v2:
 * Tweaked a comment

 translate-all.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/translate-all.c b/translate-all.c
index 7ac7916f2792..85b2b95b8afe 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -1133,19 +1133,6 @@ static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
         tb->page_addr[1] = -1;
     }
 
-    assert(((uintptr_t)tb & 3) == 0);
-    tb->jmp_list_first = (uintptr_t)tb | 2;
-    tb->jmp_list_next[0] = (uintptr_t)NULL;
-    tb->jmp_list_next[1] = (uintptr_t)NULL;
-
-    /* init original jump addresses */
-    if (tb->jmp_reset_offset[0] != TB_JMP_RESET_OFFSET_INVALID) {
-        tb_reset_jump(tb, 0);
-    }
-    if (tb->jmp_reset_offset[1] != TB_JMP_RESET_OFFSET_INVALID) {
-        tb_reset_jump(tb, 1);
-    }
-
 #ifdef DEBUG_TB_CHECK
     tb_page_check();
 #endif
@@ -1254,12 +1241,31 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
         ROUND_UP((uintptr_t)gen_code_buf + gen_code_size + search_size,
                  CODE_GEN_ALIGN);
 
+    /* init jump list */
+    assert(((uintptr_t)tb & 3) == 0);
+    tb->jmp_list_first = (uintptr_t)tb | 2;
+    tb->jmp_list_next[0] = (uintptr_t)NULL;
+    tb->jmp_list_next[1] = (uintptr_t)NULL;
+
+    /* init original jump addresses wich has been set during tcg_gen_code() */
+    if (tb->jmp_reset_offset[0] != TB_JMP_RESET_OFFSET_INVALID) {
+        tb_reset_jump(tb, 0);
+    }
+    if (tb->jmp_reset_offset[1] != TB_JMP_RESET_OFFSET_INVALID) {
+        tb_reset_jump(tb, 1);
+    }
+
     /* check next page if needed */
     virt_page2 = (pc + tb->size - 1) & TARGET_PAGE_MASK;
     phys_page2 = -1;
     if ((pc & TARGET_PAGE_MASK) != virt_page2) {
         phys_page2 = get_page_addr_code(env, virt_page2);
     }
+    /* As long as consistency of the TB stuff is provided by tb_lock in user
+     * mode and is implicit in single-threaded softmmu emulation, no explicit
+     * memory barrier is required before tb_link_page() makes the TB visible
+     * through the physical hash table and physical page list.
+     */
     tb_link_page(tb, phys_pc, phys_page2);
     return tb;
 }
-- 
2.8.1