Commit d995816b authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Andrii Nakryiko
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libbpf: Avoid reload of imm for weak, unresolved, repeating ksym 



Alexei pointed out that we can use BPF_REG_0 which already contains imm
from move_blob2blob computation. Note that we now compare the second
insn's imm, but this should not matter, since both will be zeroed out
for the error case for the insn populated earlier.

Suggested-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211122235733.634914-4-memxor@gmail.com
parent 0270090d

tools/lib/bpf/gen_loader.c

+2 −3
Original line number Diff line number Diff line
@@ -795,9 +795,8 @@ static void emit_relo_ksym_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo, 
			       kdesc->insn + offsetof(struct bpf_insn, imm));

		move_blob2blob(gen, insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm), 4,

			       kdesc->insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm));

		emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_9, BPF_REG_8, offsetof(struct bpf_insn, imm)));

		/* jump over src_reg adjustment if imm is not 0 */

		emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 3));

		/* jump over src_reg adjustment if imm is not 0, reuse BPF_REG_0 from move_blob2blob */

		emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 3));

		goto clear_src_reg;

	}

	/* remember insn offset, so we can copy BTF ID and FD later */