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ARM: net: bpf: use ldr instructions with shifted rm register

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Rather than pre-shifting the rm register for the ldr in the tail call,
shift it in the load instruction.  This eliminates one unnecessary
instruction.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Russell King 2018-07-11 10:32:17 +01:00 committed by Daniel Borkmann
parent 828e2b90e8
commit 2b6958ef11
2 changed files with 5 additions and 2 deletions
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3
arch/arm/net/bpf_jit_32.c
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@ -1096,8 +1096,7 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
r_array = arm_bpf_get_reg32(r2[1], tmp2[1], ctx);
emit(ARM_ADD_I(tmp[1], r_array, off), ctx);
r_index = arm_bpf_get_reg32(r3[1], tmp2[1], ctx);
emit(ARM_MOV_SI(tmp[0], r_index, SRTYPE_ASL, 2), ctx);
emit(ARM_LDR_R(tmp[1], tmp[1], tmp[0]), ctx);
emit(ARM_LDR_R_SI(tmp[1], tmp[1], r_index, SRTYPE_ASL, 2), ctx);
emit(ARM_CMP_I(tmp[1], 0), ctx);
_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);

4
arch/arm/net/bpf_jit_32.h
View File

@ -188,6 +188,10 @@
#define ARM_LDR_R(rt, rn, rm) (ARM_INST_LDR_R | ARM_INST_LDST__U \
| (rt) << 12 | (rn) << 16 \
| (rm))
#define ARM_LDR_R_SI(rt, rn, rm, type, imm) \
(ARM_INST_LDR_R | ARM_INST_LDST__U \
| (rt) << 12 | (rn) << 16 \
| (imm) << 7 | (type) << 5 | (rm))
#define ARM_LDRB_R(rt, rn, rm) (ARM_INST_LDRB_R | ARM_INST_LDST__U \
| (rt) << 12 | (rn) << 16 \
| (rm))