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| author | Luke Nelson <lukenels@cs.washington.edu> | 2020-04-30 19:02:09 -0700 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2020-05-04 17:04:42 +0200 |
| commit | cf48db69bdfad2930b95fd51d64444e5a7b469ae (patch) | |
| tree | 5949744e14c415cf767d9009771de173ecb8d544 /arch/arm/net | |
| parent | 60bcbc41ffb35572288681f41d1d8ab8bdb98841 (diff) | |
| download | linux-cf48db69bdfad2930b95fd51d64444e5a7b469ae.tar.bz2 | |
bpf, arm: Optimize ALU64 ARSH X using orrpl conditional instruction
This patch optimizes the code generated by emit_a32_arsh_r64, which
handles the BPF_ALU64 BPF_ARSH BPF_X instruction.
The original code uses a conditional B followed by an unconditional ORR.
The optimization saves one instruction by removing the B instruction
and using a conditional ORR (with an inverted condition).
Example of the code generated for BPF_ALU64_REG(BPF_ARSH, BPF_REG_0,
BPF_REG_1), before optimization:
34: rsb ip, r2, #32
38: subs r9, r2, #32
3c: lsr lr, r0, r2
40: orr lr, lr, r1, lsl ip
44: bmi 0x4c
48: orr lr, lr, r1, asr r9
4c: asr ip, r1, r2
50: mov r0, lr
54: mov r1, ip
and after optimization:
34: rsb ip, r2, #32
38: subs r9, r2, #32
3c: lsr lr, r0, r2
40: orr lr, lr, r1, lsl ip
44: orrpl lr, lr, r1, asr r9
48: asr ip, r1, r2
4c: mov r0, lr
50: mov r1, ip
Tested on QEMU using lib/test_bpf and test_verifier.
Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200501020210.32294-2-luke.r.nels@gmail.com
Diffstat (limited to 'arch/arm/net')
| -rw-r--r-- | arch/arm/net/bpf_jit_32.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index bf85d6db4931..48b89211ee5c 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -860,8 +860,8 @@ static inline void emit_a32_arsh_r64(const s8 dst[], const s8 src[], emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx); emit(ARM_MOV_SR(ARM_LR, rd[1], SRTYPE_LSR, rt), ctx); emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASL, ARM_IP), ctx); - _emit(ARM_COND_MI, ARM_B(0), ctx); - emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASR, tmp2[0]), ctx); + _emit(ARM_COND_PL, + ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASR, tmp2[0]), ctx); emit(ARM_MOV_SR(ARM_IP, rd[0], SRTYPE_ASR, rt), ctx); arm_bpf_put_reg32(dst_lo, ARM_LR, ctx); |