[Qemu-devel] [PATCH v3 13/15] tcg: ensure cpu_tb_exec/tb_gen_code use atomic_read/write

["Alex Bennée" <alex.bennee@linaro.org>]

To meet C11 semantics for shared data access we need to use relaxed
atomic accesses. While the completion of data writes w.r.t reads is
ensured by QHT's explicit barriers when a newly generated TB is inserted
ThreadSanitizer will still complain. By using the relaxed accesses the
same code gets generated but instrumentation does not have to worry
about a potentially undefined interaction between plain loads/stores.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 cpu-exec.c      | 6 +++---
 translate-all.c | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index e114fcd..99c906b 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -140,7 +140,7 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
     uintptr_t ret;
     TranslationBlock *last_tb;
     int tb_exit;
-    uint8_t *tb_ptr = itb->tc_ptr;
+    uint8_t *tb_ptr = atomic_read(&itb->tc_ptr);
 
     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
                            "Trace %p [" TARGET_FMT_lx "] %s\n",
@@ -291,8 +291,8 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
        is executed. */
     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
-    if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
-                 tb->flags != flags)) {
+    if (unlikely(!tb || atomic_read(&tb->pc) != pc || atomic_read(&tb->cs_base) != cs_base ||
+                 atomic_read(&tb->flags) != flags)) {
         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
         if (!tb) {
 
diff --git a/translate-all.c b/translate-all.c
index 8ca393c..0f13d4d 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -1198,10 +1198,10 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
     }
 
     gen_code_buf = tcg_ctx.code_gen_ptr;
-    tb->tc_ptr = gen_code_buf;
-    tb->cs_base = cs_base;
-    tb->flags = flags;
-    tb->cflags = cflags;
+    atomic_set(&tb->tc_ptr, gen_code_buf);
+    atomic_set(&tb->cs_base, cs_base);
+    atomic_set(&tb->flags, flags);
+    atomic_set(&tb->cflags, cflags);
 
 #ifdef CONFIG_PROFILER
     tcg_ctx.tb_count1++; /* includes aborted translations because of
-- 
2.9.3