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include/endian.h: Add 'always aligned access' support

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RISC-V doesn't support unaligned access, so check for that before
decoding and encoding. It is not perfectly performant, but still much
better then invoking the misaligned exception handler every time there
is a misaligned access. We can't modify our whole codebase to always do
aligned access, because it is neither feasible in long term nor is fair
to add that performance penalty onto other architectures that do support
unaligned access. So this is the next best thing.

On architectures that do support unaligned access the compiler will just
optimize the RISCV_ENV part out and should result in the exact same
binary.

tested: identical binary on QEMU-aarch64 and QEMU-q35.

Change-Id: I4dfccfdc2b302dd30b7ce5a29520c86add13169d
Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86609
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
This commit is contained in:
Maximilian Brune 2025-02-26 17:19:03 +01:00 • committed by Matt DeVillier
commit c444d166f3
1 changed files with 24 additions and 4 deletions
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28
src/include/endian.h
View file

@ -5,6 +5,7 @@
#include <arch/byteorder.h>
#include <stdint.h>
#include <string.h>
#include <swab.h>
#if defined(__LITTLE_ENDIAN)
@ -67,12 +68,22 @@
#define clrsetbits_le16(addr, clear, set) __clrsetbits(le, 16, addr, clear, set)
#define clrsetbits_be16(addr, clear, set) __clrsetbits(be, 16, addr, clear, set)
/* be16dec/be32dec/be64dec/le16dec/le32dec/le64dec family of functions. */
/*
* be16dec/be32dec/be64dec/le16dec/le32dec/le64dec family of functions.
* RISC-V doesn't support misaligned access so decode it byte by byte.
*/
#define DEFINE_ENDIAN_DEC(endian, width) \
static inline uint##width##_t endian##width##dec(const void *p) \
{ \
return endian##width##_to_cpu(*(uint##width##_t *)p); \
if (ENV_RISCV) { \
uint##width##_t val; \
memcpy(&val, p, sizeof(val)); \
return endian##width##_to_cpu(val); \
} else { \
return endian##width##_to_cpu(*(uint##width##_t *)p); \
} \
}
DEFINE_ENDIAN_DEC(be, 16)
DEFINE_ENDIAN_DEC(be, 32)
DEFINE_ENDIAN_DEC(be, 64)
@ -80,12 +91,21 @@ DEFINE_ENDIAN_DEC(le, 16)
DEFINE_ENDIAN_DEC(le, 32)
DEFINE_ENDIAN_DEC(le, 64)
/* be16enc/be32enc/be64enc/le16enc/le32enc/le64enc family of functions. */
/*
* be16enc/be32enc/be64enc/le16enc/le32enc/le64enc family of functions.
* RISC-V doesn't support misaligned access so encode it byte by byte.
*/
#define DEFINE_ENDIAN_ENC(endian, width) \
static inline void endian##width##enc(void *p, uint##width##_t u) \
{ \
*(uint##width##_t *)p = cpu_to_##endian##width(u); \
if (ENV_RISCV) { \
uint##width##_t val = cpu_to_##endian##width(u); \
memcpy(p, &val, sizeof(val)); \
} else { \
*(uint##width##_t *)p = cpu_to_##endian##width(u); \
} \
}
DEFINE_ENDIAN_ENC(be, 16)
DEFINE_ENDIAN_ENC(be, 32)
DEFINE_ENDIAN_ENC(be, 64)