[Qemu-devel] [PATCH v2 06/11] tcg/s390: Make direct jump patching thread-safe

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

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

Ensure direct jump patching in s390 is atomic by:
 * naturally aligning a location of direct jump address;
 * using atomic_read()/atomic_set() for code patching.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
---

Changes in v2:
 * Use QEMU_PTR_IS_ALIGNED()

 include/exec/exec-all.h   | 2 +-
 tcg/s390/tcg-target.inc.c | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 82399175fe80..e18cc24e50f0 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -320,7 +320,7 @@ static inline void tb_set_jmp_target1(uintptr_t jmp_addr, uintptr_t addr)
 {
     /* patch the branch destination */
     intptr_t disp = addr - (jmp_addr - 2);
-    stl_be_p((void*)jmp_addr, disp / 2);
+    atomic_set((int32_t *)jmp_addr, disp / 2);
     /* no need to flush icache explicitly */
 }
 #elif defined(__aarch64__)
diff --git a/tcg/s390/tcg-target.inc.c b/tcg/s390/tcg-target.inc.c
index fbf97bb2e15d..339df41cd300 100644
--- a/tcg/s390/tcg-target.inc.c
+++ b/tcg/s390/tcg-target.inc.c
@@ -219,6 +219,8 @@ typedef enum S390Opcode {
     RX_ST       = 0x50,
     RX_STC      = 0x42,
     RX_STH      = 0x40,
+
+    NOP         = 0x0707,
 } S390Opcode;
 
 #ifndef NDEBUG
@@ -1716,6 +1718,12 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
 
     case INDEX_op_goto_tb:
         if (s->tb_jmp_offset) {
+            /* branch displacement must be aligned for atomic patching;
+             * see if we need to add extra nop before branch
+             */
+            if (!QEMU_PTR_IS_ALIGNED(s->code_ptr + 1, 4)) {
+                tcg_out16(s, NOP);
+            }
             tcg_out16(s, RIL_BRCL | (S390_CC_ALWAYS << 4));
             s->tb_jmp_offset[args[0]] = tcg_current_code_size(s);
             s->code_ptr += 2;
-- 
2.8.1