From adebad07e084af91cad1b162d89c86c9e08e0a31 Mon Sep 17 00:00:00 2001 From: Mans Rullgard Date: Wed, 2 May 2012 12:46:22 +0100 Subject: [PATCH] arm: intreadwrite: fix inline asm constraints for gcc 4.6 and later With a dereferenced type-cast pointer as memory operand, gcc 4.6 and later will sometimes copy the data to a temporary location, the address of which is used as the operand value, if it thinks the target address might be misaligned. Using a pointer to a packed struct type instead does the right thing. The 16-bit case is special since the ldrh instruction addressing modes are limited compared to ldr. The "Uq" constraint produces a memory reference suitable for an ldrsb instruction, which supports the same addressing modes as ldrh. However, the restrictions appear to apply only when the operand addresses a single byte. The memory reference must thus be split into two operands each targeting one byte. Finally, the "Uq" constraint is only available in ARM mode. The Thumb-2 ldrh instruction supports most addressing modes so the normal "m" constraint can be used there. Signed-off-by: Mans Rullgard --- libavutil/arm/intreadwrite.h | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/libavutil/arm/intreadwrite.h b/libavutil/arm/intreadwrite.h index 613abe511c..ec92d4d04b 100644 --- a/libavutil/arm/intreadwrite.h +++ b/libavutil/arm/intreadwrite.h @@ -27,8 +27,13 @@ #define AV_RN16 AV_RN16 static av_always_inline unsigned AV_RN16(const void *p) { + const uint8_t *q = p; unsigned v; - __asm__ ("ldrh %0, %1" : "=r"(v) : "m"(*(const uint16_t *)p)); +#ifdef __thumb__ + __asm__ ("ldrh %0, %1" : "=r"(v) : "m"(q[0]), "m"(q[1])); +#else + __asm__ ("ldrh %0, %1" : "=r"(v) : "Uq"(q[0]), "m"(q[1])); +#endif return v; } @@ -41,8 +46,9 @@ static av_always_inline void AV_WN16(void *p, uint16_t v) #define AV_RN32 AV_RN32 static av_always_inline uint32_t AV_RN32(const void *p) { + const struct __attribute__((packed)) { uint32_t v; } *q = p; uint32_t v; - __asm__ ("ldr %0, %1" : "=r"(v) : "m"(*(const uint32_t *)p)); + __asm__ ("ldr %0, %1" : "=r"(v) : "m"(*q)); return v; } @@ -55,11 +61,12 @@ static av_always_inline void AV_WN32(void *p, uint32_t v) #define AV_RN64 AV_RN64 static av_always_inline uint64_t AV_RN64(const void *p) { + const struct __attribute__((packed)) { uint32_t v; } *q = p; uint64_t v; __asm__ ("ldr %Q0, %1 \n\t" "ldr %R0, %2 \n\t" : "=&r"(v) - : "m"(*(const uint32_t*)p), "m"(*((const uint32_t*)p+1))); + : "m"(q[0]), "m"(q[1])); return v; }