[Qemu-devel] [PATCH v2 08/11] tcg/aarch64: Make direct jump patching thread-safe

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

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

Ensure direct jump patching in AArch64 is atomic by 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 tcg_debug_assert() instead of assert()

 tcg/aarch64/tcg-target.inc.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
index 0ed10a974121..29839765b828 100644
--- a/tcg/aarch64/tcg-target.inc.c
+++ b/tcg/aarch64/tcg-target.inc.c
@@ -73,6 +73,18 @@ static inline void reloc_pc26(tcg_insn_unit *code_ptr, tcg_insn_unit *target)
     *code_ptr = deposit32(*code_ptr, 0, 26, offset);
 }
 
+static inline void reloc_pc26_atomic(tcg_insn_unit *code_ptr,
+                                     tcg_insn_unit *target)
+{
+    ptrdiff_t offset = target - code_ptr;
+    tcg_insn_unit insn;
+    tcg_debug_assert(offset == sextract64(offset, 0, 26));
+    /* read instruction, mask away previous PC_REL26 parameter contents,
+       set the proper offset, then write back the instruction. */
+    insn = atomic_read(code_ptr);
+    atomic_set(code_ptr, deposit32(insn, 0, 26, offset));
+}
+
 static inline void reloc_pc19(tcg_insn_unit *code_ptr, tcg_insn_unit *target)
 {
     ptrdiff_t offset = target - code_ptr;
@@ -835,7 +847,7 @@ void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
     tcg_insn_unit *code_ptr = (tcg_insn_unit *)jmp_addr;
     tcg_insn_unit *target = (tcg_insn_unit *)addr;
 
-    reloc_pc26(code_ptr, target);
+    reloc_pc26_atomic(code_ptr, target);
     flush_icache_range(jmp_addr, jmp_addr + 4);
 }
 
-- 
2.8.1