]> git.baikalelectronics.ru Git - kernel.git/commit
bpf, arm: Optimize ALU ARSH K using asr immediate instruction
authorLuke Nelson <lukenels@cs.washington.edu>
Fri, 1 May 2020 02:02:10 +0000 (19:02 -0700)
committerDaniel Borkmann <daniel@iogearbox.net>
Mon, 4 May 2020 15:04:42 +0000 (17:04 +0200)
commit01acbf9bb35cb35bbc2ad05150e731c9e28c7179
tree86f5d9bfc42c012d4553fdfe6a79aebb228c6584
parent6cdf870e6cf4a169b40f7eece57d23af6ff71e2a
bpf, arm: Optimize ALU ARSH K using asr immediate instruction

This patch adds an optimization that uses the asr immediate instruction
for BPF_ALU BPF_ARSH BPF_K, rather than loading the immediate to
a temporary register. This is similar to existing code for handling
BPF_ALU BPF_{LSH,RSH} BPF_K. This optimization saves two instructions
and is more consistent with LSH and RSH.

Example of the code generated for BPF_ALU32_IMM(BPF_ARSH, BPF_REG_0, 5)
before the optimization:

  2c:  mov    r8, #5
  30:  mov    r9, #0
  34:  asr    r0, r0, r8

and after optimization:

  2c:  asr    r0, r0, #5

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/20200501020210.32294-3-luke.r.nels@gmail.com
arch/arm/net/bpf_jit_32.c
arch/arm/net/bpf_jit_32.h