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| author |   Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2021-11-23 05:27:32 +0530 |
|---|---|---|
| committer |   Andrii Nakryiko <andrii@kernel.org> | 2021-11-30 15:48:14 -0800 |
| commit | 0270090d396a8e7e7f42adae13fdfa48ffb85144 (patch) | |
| tree | c0dd5b0d7e0ee3bd07d2e6dea0f1cbf6e2a980ac /tools/lib/bpf/gen_loader.c | |
| parent | bpf: Change bpf_kallsyms_lookup_name size type to ARG_CONST_SIZE_OR_ZERO (diff) | |
| download | linux-dev-0270090d396a8e7e7f42adae13fdfa48ffb85144.tar.xz linux-dev-0270090d396a8e7e7f42adae13fdfa48ffb85144.zip | |
libbpf: Avoid double stores for success/failure case of ksym relocations
Instead, jump directly to success case stores in case ret >= 0, else do
the default 0 value store and jump over the success case. This is better
in terms of readability. Readjust the code for kfunc relocation as well
to follow a similar pattern, also leads to easier to follow code now.
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211122235733.634914-3-memxor@gmail.com
Diffstat (limited to '')
| -rw-r--r-- | tools/lib/bpf/gen_loader.c | 37 |
1 files changed, 21 insertions, 16 deletions
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c index c7bc77f4e752..5a2d6bf041dd 100644 --- a/tools/lib/bpf/gen_loader.c +++ b/tools/lib/bpf/gen_loader.c @@ -674,27 +674,29 @@ static void emit_relo_kfunc_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo return; } kdesc->off = btf_fd_idx; - /* set a default value for imm */ + /* jump to success case */ + emit(gen, BPF_JMP_IMM(BPF_JSGE, BPF_REG_7, 0, 3)); + /* set value for imm, off as 0 */ emit(gen, BPF_ST_MEM(BPF_W, BPF_REG_8, offsetof(struct bpf_insn, imm), 0)); - /* skip success case store if ret < 0 */ - emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 1)); + emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0)); + /* skip success case for ret < 0 */ + emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 10)); /* store btf_id into insn[insn_idx].imm */ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7, offsetof(struct bpf_insn, imm))); + /* obtain fd in BPF_REG_9 */ + emit(gen, BPF_MOV64_REG(BPF_REG_9, BPF_REG_7)); + emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32)); + /* jump to fd_array store if fd denotes module BTF */ + emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 2)); + /* set the default value for off */ + emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0)); + /* skip BTF fd store for vmlinux BTF */ + emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 4)); /* load fd_array slot pointer */ emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE, 0, 0, 0, blob_fd_array_off(gen, btf_fd_idx))); - /* skip store of BTF fd if ret < 0 */ - emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 3)); /* store BTF fd in slot */ - emit(gen, BPF_MOV64_REG(BPF_REG_9, BPF_REG_7)); - emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32)); emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_9, 0)); - /* set a default value for off */ - emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0)); - /* skip insn->off store if ret < 0 */ - emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 2)); - /* skip if vmlinux BTF */ - emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_9, 0, 1)); /* store index into insn[insn_idx].off */ emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), btf_fd_idx)); log: @@ -803,17 +805,20 @@ static void emit_relo_ksym_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo, emit_bpf_find_by_name_kind(gen, relo); if (!relo->is_weak) emit_check_err(gen); - /* set default values as 0 */ + /* jump to success case */ + emit(gen, BPF_JMP_IMM(BPF_JSGE, BPF_REG_7, 0, 3)); + /* set values for insn[insn_idx].imm, insn[insn_idx + 1].imm as 0 */ emit(gen, BPF_ST_MEM(BPF_W, BPF_REG_8, offsetof(struct bpf_insn, imm), 0)); emit(gen, BPF_ST_MEM(BPF_W, BPF_REG_8, sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm), 0)); - /* skip success case stores if ret < 0 */ - emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 4)); + /* skip success case for ret < 0 */ + emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 4)); /* store btf_id into insn[insn_idx].imm */ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7, offsetof(struct bpf_insn, imm))); /* store btf_obj_fd into insn[insn_idx + 1].imm */ emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_7, 32)); emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7, sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm))); + /* skip src_reg adjustment */ emit(gen, BPF_JMP_IMM(BPF_JSGE, BPF_REG_7, 0, 3)); clear_src_reg: /* clear bpf_object__relocate_data's src_reg assignment, otherwise we get a verifier failure */ |