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Commit 828e2b90 authored by Russell King's avatar Russell King Committed by Daniel Borkmann
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ARM: net: bpf: use immediate forms of instructions where possible 



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: default avatarRussell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 1ca3b17b

arch/arm/net/bpf_jit_32.c

+12 −9
Original line number Diff line number Diff line
@@ -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);

arch/arm/net/bpf_jit_32.h

+1 −0
Original line number Diff line number Diff line
@@ -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