[Qemu-devel] [PATCH v4 02/10] tcg: Use uintptr_t type for jmp_list_{next|first} fields of TB

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

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

These fields do not contain pure pointers to a TranslationBlock
structure. So uintptr_t is the most appropriate type for them.
Also put some asserts to assure that the two least significant bits of
the pointer are always zero before assigning it to jmp_list_first.

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:
 * Removed assert from tb_add_jump()
 * Minor commit message rewording
Changes in v2:
 * Eliminated duplicate dereference of 'ptb' in tb_jmp_remove()

 include/exec/exec-all.h | 12 +++++++-----
 translate-all.c         | 38 ++++++++++++++++++++------------------
 2 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 38a149cc5e0c..03b177b0cac5 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -275,14 +275,16 @@ struct TranslationBlock {
      * jmp_list_first points to the first TB jumping to this one.
      * jmp_list_next is used to point to the next TB in a list.
      * Since each TB can have two jumps, it can participate in two lists.
-     * The two least significant bits of a pointer are used to choose which
-     * data field holds a pointer to the next TB:
+     * jmp_list_first and jmp_list_next are 4-byte aligned pointers to a
+     * TranslationBlock structure, but the two least significant bits of
+     * them are used to encode which data field of the pointed TB should
+     * be used to traverse the list further from that TB:
      * 0 => jmp_list_next[0], 1 => jmp_list_next[1], 2 => jmp_list_first.
      * In other words, 0/1 tells which jump is used in the pointed TB,
      * and 2 means that this is a pointer back to the target TB of this list.
      */
-    struct TranslationBlock *jmp_list_next[2];
-    struct TranslationBlock *jmp_list_first;
+    uintptr_t jmp_list_next[2];
+    uintptr_t jmp_list_first;
 };
 
 #include "qemu/thread.h"
@@ -401,7 +403,7 @@ static inline void tb_add_jump(TranslationBlock *tb, int n,
 
         /* add in TB jmp circular list */
         tb->jmp_list_next[n] = tb_next->jmp_list_first;
-        tb_next->jmp_list_first = (TranslationBlock *)((uintptr_t)tb | n);
+        tb_next->jmp_list_first = (uintptr_t)tb | n;
     }
 }
 
diff --git a/translate-all.c b/translate-all.c
index 33ca06c663d4..ba71ff73f55f 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -927,17 +927,17 @@ static inline void tb_page_remove(TranslationBlock **ptb, TranslationBlock *tb)
 
 static inline void tb_jmp_remove(TranslationBlock *tb, int n)
 {
-    TranslationBlock *tb1, **ptb;
+    TranslationBlock *tb1;
+    uintptr_t *ptb, ntb;
     unsigned int n1;
 
     ptb = &tb->jmp_list_next[n];
-    tb1 = *ptb;
-    if (tb1) {
+    if (*ptb) {
         /* find tb(n) in circular list */
         for (;;) {
-            tb1 = *ptb;
-            n1 = (uintptr_t)tb1 & 3;
-            tb1 = (TranslationBlock *)((uintptr_t)tb1 & ~3);
+            ntb = *ptb;
+            n1 = ntb & 3;
+            tb1 = (TranslationBlock *)(ntb & ~3);
             if (n1 == n && tb1 == tb) {
                 break;
             }
@@ -950,7 +950,7 @@ static inline void tb_jmp_remove(TranslationBlock *tb, int n)
         /* now we can suppress tb(n) from the list */
         *ptb = tb->jmp_list_next[n];
 
-        tb->jmp_list_next[n] = NULL;
+        tb->jmp_list_next[n] = (uintptr_t)NULL;
     }
 }
 
@@ -969,7 +969,7 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
     PageDesc *p;
     unsigned int h, n1;
     tb_page_addr_t phys_pc;
-    TranslationBlock *tb1, *tb2;
+    uintptr_t tb1, tb2;
 
     /* remove the TB from the hash list */
     phys_pc = tb->page_addr[0] + (tb->pc & ~TARGET_PAGE_MASK);
@@ -1005,19 +1005,20 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
     /* suppress any remaining jumps to this TB */
     tb1 = tb->jmp_list_first;
     for (;;) {
-        n1 = (uintptr_t)tb1 & 3;
+        TranslationBlock *tmp_tb;
+        n1 = tb1 & 3;
         if (n1 == 2) {
             break;
         }
-        tb1 = (TranslationBlock *)((uintptr_t)tb1 & ~3);
-        tb2 = tb1->jmp_list_next[n1];
-        tb_reset_jump(tb1, n1);
-        tb1->jmp_list_next[n1] = NULL;
+        tmp_tb = (TranslationBlock *)(tb1 & ~3);
+        tb2 = tmp_tb->jmp_list_next[n1];
+        tb_reset_jump(tmp_tb, n1);
+        tmp_tb->jmp_list_next[n1] = (uintptr_t)NULL;
         tb1 = tb2;
     }
 
-    /* fail safe */
-    tb->jmp_list_first = (TranslationBlock *)((uintptr_t)tb | 2);
+    assert(((uintptr_t)tb & 3) == 0);
+    tb->jmp_list_first = (uintptr_t)tb | 2; /* fail safe */
 
     tcg_ctx.tb_ctx.tb_phys_invalidate_count++;
 }
@@ -1491,9 +1492,10 @@ static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
         tb->page_addr[1] = -1;
     }
 
-    tb->jmp_list_first = (TranslationBlock *)((uintptr_t)tb | 2);
-    tb->jmp_list_next[0] = NULL;
-    tb->jmp_list_next[1] = NULL;
+    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) {
-- 
2.8.1