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[PW_SID:1163154] riscv: runtime enablement for native misaligned ucopy #2646

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[PW_SID:1163154] riscv: runtime enablement for native misaligned ucopy #2646

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af984d1
riscv: introduce assembly version of jump table
tchiu-TT Sep 11, 2026
e89b294
riscv: optmize ucopy for has_fast_unaligned_accesses
tchiu-TT Sep 11, 2026
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26 changes: 26 additions & 0 deletions arch/riscv/include/asm/jump_label.h
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,32 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke
label:
return true;
}
#else
#include <asm/asm.h>

#define JUMP_TABLE_ENTRY(key, label) \
.pushsection __jump_table, "aw"; \
.align RISCV_LGPTR; \
.long 1b - ., label - .; \
RISCV_PTR key - .; \
.popsection

#define ARCH_STATIC_BRANCH_ASM(key, label) \
.align 2; \
.option push; \
.option norelax; \
.option norvc; \
1: nop; \
.option pop; \
JUMP_TABLE_ENTRY(key, label)

#define ARCH_STATIC_BRANCH_JUMP_ASM(key, label) \
.align 2; \
.option push; \
.option norelax; \
.option norvc; \
1: j label; \
.option pop; \
JUMP_TABLE_ENTRY(key, label)
#endif /* __ASSEMBLER__ */
#endif /* __ASM_JUMP_LABEL_H */
61 changes: 34 additions & 27 deletions arch/riscv/lib/uaccess.S
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
#include <asm/csr.h>
#include <asm/hwcap.h>
#include <asm/alternative-macros.h>
#include <asm/jump_label.h>

.macro fixup op reg addr lbl
100:
Expand Down Expand Up @@ -77,33 +78,11 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled)
bltu a2, a3, .Lbyte_copy_tail

#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
/*
* Copy first bytes until dst is aligned to word boundary.
* a0 - start of dst
* t1 - start of aligned dst
*/
addi t1, a0, SZREG-1
andi t1, t1, ~(SZREG-1)
/* dst is already aligned, skip */
beq a0, t1, .Lskip_align_dst
1:
/* a5 - one byte for copying data */
fixup lb a5, 0(a1), 10f
addi a1, a1, 1 /* src */
fixup sb a5, 0(a0), 10f
addi a0, a0, 1 /* dst */
bltu a0, t1, 1b /* t1 - start of aligned dst */

.Lskip_align_dst:
/*
* Now dst is aligned.
* Use shift-copy if src is misaligned.
* Use word-copy if both src and dst are aligned because
* can not use shift-copy which do not require shifting
*/
/* a1 - start of src */
andi a3, a1, SZREG-1
bnez a3, .Lshift_copy
#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) && defined(CONFIG_JUMP_LABEL)
ARCH_STATIC_BRANCH_JUMP_ASM(fast_unaligned_access_speed_key + 1, .Lalign_dst)
#else
j .Lalign_dst
#endif
#endif
.Lword_copy:
/*
Expand Down Expand Up @@ -139,6 +118,34 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled)
j .Lbyte_copy_tail

#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
.Lalign_dst:
/*
* Copy first bytes until dst is aligned to word boundary.
* a0 - start of dst
* t1 - start of aligned dst
*/
addi t1, a0, SZREG-1
andi t1, t1, ~(SZREG-1)
/* dst is already aligned, skip */
beq a0, t1, .Lskip_align_dst
1:
/* a5 - one byte for copying data */
fixup lb a5, 0(a1), 10f
addi a1, a1, 1 /* src */
fixup sb a5, 0(a0), 10f
addi a0, a0, 1 /* dst */
bltu a0, t1, 1b /* t1 - start of aligned dst */

.Lskip_align_dst:
/*
* Now dst is aligned.
* Use shift-copy if src is misaligned.
* Use word-copy if both src and dst are aligned because
* can not use shift-copy which do not require shifting
*/
/* a1 - start of src */
andi a3, a1, SZREG-1
beqz a3, .Lword_copy
.Lshift_copy:

/*
Expand Down