From bb8d75bf3119802a286cb36d8575febece9b20d7 Mon Sep 17 00:00:00 2001 From: Frediano Ziglio Date: Sun, 24 Dec 2017 13:21:45 +0000 Subject: [PATCH] canvas_base: Avoid misaligned access decoding LZ4 data Make code faster on platforms not supporting unaligned access by default. SPICE_UNALIGNED_CAST is just silencing possible alignment warning and, if enabled, produces some logs, however in this case we know that the pointer can be misaligned. Use packed structures to tell compiler to generate best code possible. For more details see comment on commit 74e50b57ae05116be4e2 ("Make the compiler work out better way to write unaligned memory"). Signed-off-by: Frediano Ziglio Acked-by: Christophe Fergeau --- common/canvas_base.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/common/canvas_base.c b/common/canvas_base.c index 276f67c..2fd60aa 100644 --- a/common/canvas_base.c +++ b/common/canvas_base.c @@ -45,6 +45,14 @@ #include "mem.h" #include "macros.h" +#include +typedef struct SPICE_ATTR_PACKED { + uint32_t v; +} uint32_unaligned_t; +#include + +#define read_uint32_be(ptr) ntohl(((uint32_unaligned_t *)(ptr))->v) + #define ROUND(_x) ((int)floor((_x) + 0.5)) static inline int fix_to_int(SPICE_FIXED28_4 fixed) @@ -572,7 +580,7 @@ static pixman_image_t *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image) do { // Read next compressed block - enc_size = ntohl(*SPICE_UNALIGNED_CAST(uint32_t *, data)); + enc_size = read_uint32_be(data); data += 4; dec_size = LZ4_decompress_safe_continue(stream, (const char *) data, (char *) dest, enc_size, available);