Compared to decode_instruction(), decode_instruction_stream() has an additional
stream parameter which avoids some guest memory accesses during instruction
decoding. Both functions defer the actual work to decode_opcode() which would
set the stream pointer to zero such that decode_instruction_stream() essentially
behaved like decode_instruction(). Given that all callers of
decode_instruction_stream() properly zero-initialize the decode parameter, the
memset() call can be moved into decode_instruction() which is the only other
user of decode_opcode(). This preserves the non-zero stream pointer which
avoids extra guest memory accesses.
Fixes: 1e25327b244a ("target/i386/emulate: Allow instruction decoding from
stream")
cc: qemu-stable
Signed-off-by: Bernhard Beschow <[email protected]>
---
target/i386/emulate/x86_decode.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/target/i386/emulate/x86_decode.c b/target/i386/emulate/x86_decode.c
index 6ad03b71b0..7bbcd2a9a2 100644
--- a/target/i386/emulate/x86_decode.c
+++ b/target/i386/emulate/x86_decode.c
@@ -2088,8 +2088,6 @@ static void decode_opcodes(CPUX86State *env, struct
x86_decode *decode)
static uint32_t decode_opcode(CPUX86State *env, struct x86_decode *decode)
{
- memset(decode, 0, sizeof(*decode));
-
decode_prefix(env, decode);
set_addressing_size(env, decode);
set_operand_size(env, decode);
@@ -2101,6 +2099,8 @@ static uint32_t decode_opcode(CPUX86State *env, struct
x86_decode *decode)
uint32_t decode_instruction(CPUX86State *env, struct x86_decode *decode)
{
+ memset(decode, 0, sizeof(*decode));
+
return decode_opcode(env, decode);
}
--
2.53.0
