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ARM: net: bpf: use immediate forms of instructions where possible

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Rather than moving constants to a register and then using them in a
subsequent instruction, use them directly in the desired instruction
cutting out the "middle" register.  This removes two instructions from
the tail call code path.

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 10:32:12 +01:00 committed by Daniel Borkmann
parent 1ca3b17b77
commit 828e2b90e8
2 changed files with 13 additions and 9 deletions
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21
arch/arm/net/bpf_jit_32.c
View File

@ -304,7 +304,7 @@ static u32 arm_bpf_ldst_imm12(u32 op, u8 rt, u8 rn, s16 imm12)
op |= ARM_INST_LDST__U;
else
imm12 = -imm12;
return op | (imm12 & 0xfff);
return op | (imm12 & ARM_INST_LDST__IMM12);
}
static u32 arm_bpf_ldst_imm8(u32 op, u8 rt, u8 rn, s16 imm8)
@ -1054,17 +1054,19 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
const int idx0 = ctx->idx;
#define cur_offset (ctx->idx - idx0)
#define jmp_offset (out_offset - (cur_offset) - 2)
u32 off, lo, hi;
u32 lo, hi;
s8 r_array, r_index;
int off;
/* if (index >= array->map.max_entries)
* goto out;
*/
BUILD_BUG_ON(offsetof(struct bpf_array, map.max_entries) >
ARM_INST_LDST__IMM12);
off = offsetof(struct bpf_array, map.max_entries);
/* array->map.max_entries */
emit_a32_mov_i(tmp[1], off, ctx);
r_array = arm_bpf_get_reg32(r2[1], tmp2[1], ctx);
emit(ARM_LDR_R(tmp[1], r_array, tmp[1]), ctx);
emit(ARM_LDR_I(tmp[1], r_array, off), ctx);
/* index is 32-bit for arrays */
r_index = arm_bpf_get_reg32(r3[1], tmp2[1], ctx);
/* index >= array->map.max_entries */
@ -1089,10 +1091,10 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
* if (prog == NULL)
* goto out;
*/
off = offsetof(struct bpf_array, ptrs);
emit_a32_mov_i(tmp[1], off, ctx);
BUILD_BUG_ON(imm8m(offsetof(struct bpf_array, ptrs)) < 0);
off = imm8m(offsetof(struct bpf_array, ptrs));
r_array = arm_bpf_get_reg32(r2[1], tmp2[1], ctx);
emit(ARM_ADD_R(tmp[1], r_array, tmp[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);
@ -1100,9 +1102,10 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
_emit(ARM_COND_EQ, ARM_B(jmp_offset), ctx);
/* goto *(prog->bpf_func + prologue_size); */
BUILD_BUG_ON(offsetof(struct bpf_prog, bpf_func) >
ARM_INST_LDST__IMM12);
off = offsetof(struct bpf_prog, bpf_func);
emit_a32_mov_i(tmp2[1], off, ctx);
emit(ARM_LDR_R(tmp[1], tmp[1], tmp2[1]), ctx);
emit(ARM_LDR_I(tmp[1], tmp[1], off), ctx);
emit(ARM_ADD_I(tmp[1], tmp[1], ctx->prologue_bytes), ctx);
emit_bx_r(tmp[1], ctx);

1
arch/arm/net/bpf_jit_32.h
View File

@ -78,6 +78,7 @@
#define ARM_INST_EOR_I 0x02200000
#define ARM_INST_LDST__U 0x00800000
#define ARM_INST_LDST__IMM12 0x00000fff
#define ARM_INST_LDRB_I 0x05500000
#define ARM_INST_LDRB_R 0x07d00000
#define ARM_INST_LDRH_I 0x015000b0