tcg: Avoid undefined behaviour patching code at unaligned addresses

To avoid C undefined behaviour when patching generated code,
provide wrappers tcg_patch8/16/32/64 which use the usual memcpy
trick, and use them in the i386 backend.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 293f00bc5a..31a5d48d03 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -122,6 +122,11 @@ static inline void tcg_out8(TCGContext *s, uint8_t v)
     *s->code_ptr++ = v;
 }
 
+static inline void tcg_patch8(uint8_t *p, uint8_t v)
+{
+    memcpy(p, &v, sizeof(v));
+}
+
 static inline void tcg_out16(TCGContext *s, uint16_t v)
 {
     uint8_t *p = s->code_ptr;
@@ -129,6 +134,11 @@ static inline void tcg_out16(TCGContext *s, uint16_t v)
     s->code_ptr = p + 2;
 }
 
+static inline void tcg_patch16(uint8_t *p, uint16_t v)
+{
+    memcpy(p, &v, sizeof(v));
+}
+
 static inline void tcg_out32(TCGContext *s, uint32_t v)
 {
     uint8_t *p = s->code_ptr;
@@ -136,6 +146,11 @@ static inline void tcg_out32(TCGContext *s, uint32_t v)
     s->code_ptr = p + 4;
 }
 
+static inline void tcg_patch32(uint8_t *p, uint32_t v)
+{
+    memcpy(p, &v, sizeof(v));
+}
+
 static inline void tcg_out64(TCGContext *s, uint64_t v)
 {
     uint8_t *p = s->code_ptr;
@@ -143,6 +158,11 @@ static inline void tcg_out64(TCGContext *s, uint64_t v)
     s->code_ptr = p + 8;
 }
 
+static inline void tcg_patch64(uint8_t *p, uint64_t v)
+{
+    memcpy(p, &v, sizeof(v));
+}
+
 /* label relocation processing */
 
 static void tcg_out_reloc(TCGContext *s, uint8_t *code_ptr, int type,