Re: [PATCH bpf-next v2 2/8] libbpf: Add typeless ksym support to gen_loader
From: Song Liu <hidden>
Date: 2021-10-14 16:40:10
Also in:
bpf
On Oct 13, 2021, at 12:33 AM, Kumar Kartikeya Dwivedi [off-list ref] wrote: This uses the bpf_kallsyms_lookup_name helper added in previous patches to relocate typeless ksyms. The return value ENOENT can be ignored, and the value written to 'res' can be directly stored to the insn, as it is overwritten to 0 on lookup failure. For repeating symbols, we can simply copy the previously populated bpf_insn. Also, we need to take care to not close fds for typeless ksym_desc, so reuse the 'off' member's space to add a marker for typeless ksym and use that to skip them in cleanup_relos. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
[...]
} +/* Expects: + * BPF_REG_8 - pointer to instruction + */ +static void emit_relo_ksym_typeless(struct bpf_gen *gen, + struct ksym_relo_desc *relo, int insn)
This function has quite some duplicated logic as emit_relo_ksym_btf(). I guess we can somehow reuse the code here. Say, we pull changes from 3/8 first to handle weak type. Then we extend the function to handle typeless. Would this work?
+{
+ struct ksym_desc *kdesc;
+
+ kdesc = get_ksym_desc(gen, relo);
+ if (!kdesc)
+ return;
+ /* try to copy from existing ldimm64 insn */
+ if (kdesc->ref > 1) {
+ move_blob2blob(gen, insn + offsetof(struct bpf_insn, imm), 4,
+ 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));
+ goto log;
+ }
+ /* remember insn offset, so we can copy ksym addr later */
+ kdesc->insn = insn;
+ /* skip typeless ksym_desc in fd closing loop in cleanup_relos */
+ kdesc->typeless = true;
+ emit_bpf_kallsyms_lookup_name(gen, relo);
+ emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_7, -ENOENT, 1));
+ emit_check_err(gen);
+ /* store lower half of addr into insn[insn_idx].imm */
+ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_9, offsetof(struct bpf_insn, imm)));
+ /* store upper half of addr into insn[insn_idx + 1].imm */
+ emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32));
+ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_9,
+ sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm)));
+log:
+ if (!gen->log_level)
+ return;
+ emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_8,
+ offsetof(struct bpf_insn, imm)));
+ emit(gen, BPF_LDX_MEM(BPF_H, BPF_REG_9, BPF_REG_8, sizeof(struct bpf_insn) +
+ offsetof(struct bpf_insn, imm)));
+ debug_regs(gen, BPF_REG_7, BPF_REG_9, " var t=0 w=%d (%s:count=%d): imm[0]: %%d, imm[1]: %%d",
+ relo->is_weak, relo->name, kdesc->ref);
+ emit(gen, BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_8, offsetofend(struct bpf_insn, code)));
+ debug_regs(gen, BPF_REG_9, -1, " var t=0 w=%d (%s:count=%d): insn.reg",
+ relo->is_weak, relo->name, kdesc->ref);[...]
quoted hunk ↗ jump to hunk
+++ b/tools/lib/bpf/libbpf.c@@ -6355,17 +6355,14 @@ static int bpf_program__record_externs(struct bpf_program *prog)case RELO_EXTERN_VAR: if (ext->type != EXT_KSYM) continue; - if (!ext->ksym.type_id) { - pr_warn("typeless ksym %s is not supported yet\n", - ext->name); - return -ENOTSUP; - } - bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak, + bpf_gen__record_extern(obj->gen_loader, ext->name, + ext->is_weak, !ext->ksym.type_id, BTF_KIND_VAR, relo->insn_idx); break; case RELO_EXTERN_FUNC: - bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak, - BTF_KIND_FUNC, relo->insn_idx); + bpf_gen__record_extern(obj->gen_loader, ext->name, + ext->is_weak, 0, BTF_KIND_FUNC,
nit: Prefer use "false" for bool arguments.
+ relo->insn_idx); break; default: continue; -- 2.33.0