> On Oct 13, 2021, at 12:33 AM, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > This extends existing ksym relocation code to also support relocating > weak ksyms. Care needs to be taken to zero out the src_reg (currently > BPF_PSEUOD_BTF_ID, always set for gen_loader by bpf_object__relocate_data) > when the BTF ID lookup fails at runtime. This is not a problem for > libbpf as it only sets ext->is_set when BTF ID lookup succeeds (and only > proceeds in case of failure if ext->is_weak, leading to src_reg > remaining as 0 for weak unresolved ksym). [...] > 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))); > -log: > + 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 */ > +#if defined(__LITTLE_ENDIAN_BITFIELD) > + reg_mask = 0x0f; /* src_reg,dst_reg,... */ > +#elif defined(__BIG_ENDIAN_BITFIELD) > + reg_mask = 0xf0; /* dst_reg,src_reg,... */ > +#else > +#error "Unsupported bit endianness, cannot proceed" > +#endif nit: Please put the "if defined" block in an inline helper. > + emit(gen, BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_8, offsetofend(struct bpf_insn, code))); > + emit(gen, BPF_ALU32_IMM(BPF_AND, BPF_REG_9, reg_mask)); > + emit(gen, BPF_STX_MEM(BPF_B, BPF_REG_8, BPF_REG_9, offsetofend(struct bpf_insn, code))); > + > if (!gen->log_level) > return; > emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_8,
