On SMP systems, the global percpu variables are placed in a speical '.data..percpu' section, which is stored in a segment whose initial address is set to 0, the addresses of per-CPU variables are relative positive addresses[1]. This patch extracts these variables from vmlinux and places them with their type information in BTF, so that they can be accessed in BPF. In a v5.7-rc7 linux kernel, I was able to extract 291 such variables. The space overhead is small. Testing: Before: $ readelf -SW vmlinux | grep BTF [25] .BTF PROGBITS ffffffff821a905c 13a905c 2d2bf8 00 A 0 0 1 After: $ pahole -J vmlinux $ readelf -SW vmlinux | grep BTF [25] .BTF PROGBITS ffffffff821a905c 13a905c 2d4db8 00 A 0 0 1 Common percpu vars can be found in the BTF section. $ bpftool btf dump file vmlinux | grep runqueues [14098] VAR 'runqueues' type_id=13725, linkage=global-alloc $ bpftool btf dump file vmlinux | grep cpu_stopper [17589] STRUCT 'cpu_stopper' size=72 vlen=5 [17609] VAR 'cpu_stopper' type_id=17589, linkage=global-alloc References: [1] https://lwn.net/Articles/531148/ Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx> --- btf_encoder.c | 27 +++++++++++++++++++++++++++ libbtf.c | 29 +++++++++++++++++++++++++++++ libbtf.h | 2 ++ pahole.c | 1 + 4 files changed, 59 insertions(+) diff --git a/btf_encoder.c b/btf_encoder.c index df16ba0..f550f34 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -241,6 +241,33 @@ int cu__encode_btf(struct cu *cu, int verbose) } } + cu__for_each_variable(cu, core_id, pos) { + int btf_var_id; + struct variable *var; + uint32_t linkage; + + var = tag__variable(pos); + /* + * .data..percpu is stored in a segment whose initial address is + * set to 0, the addresses of per-CPU variables are addresses + * relative to 0. + * + * https://lwn.net/Articles/531148/ + */ + if ((int64_t)var->ip.addr <= 0) + continue; + linkage = variable__scope(var) == VSCOPE_GLOBAL; + btf_var_id = btf_elf__add_var_type(btfe, var->ip.tag.type, + var->name, linkage, + type_id_off); + if (btf_var_id < 0) { + err = -1; + printf("error: failed to encode variable '%s'\n", + variable__name(var, cu)); + goto out; + } + } + out: if (err) btf_elf__delete(btfe); diff --git a/libbtf.c b/libbtf.c index 2fbce40..de85666 100644 --- a/libbtf.c +++ b/libbtf.c @@ -613,6 +613,35 @@ int32_t btf_elf__add_func_proto(struct btf_elf *btfe, struct ftype *ftype, uint3 return type_id; } +int32_t btf_elf__add_var_type(struct btf_elf *btfe, uint32_t type, + uint32_t name_off, uint32_t linkage, + uint32_t type_id_off) +{ + struct { + struct btf_type type; + struct btf_var var; + } t; + + t.type.name_off = name_off; + t.type.info = BTF_INFO_ENCODE(BTF_KIND_VAR, 0, 0); + t.type.type = type_id_off + type; + + t.var.linkage = linkage; + + ++btfe->type_index; + if (gobuffer__add(&btfe->types, &t.type, sizeof(t)) < 0) { + btf_elf__log_type(btfe, &t.type, true, true, + "type=%u name=%s Error in adding gobuffer", + t.type.type, btf_elf__name_in_gobuf(btfe, t.type.name_off)); + return -1; + } + + btf_elf__log_type(btfe, &t.type, false, false, "type=%u name=%s", + t.type.type, btf_elf__name_in_gobuf(btfe, t.type.name_off)); + + return btfe->type_index; +} + static int btf_elf__write(const char *filename, struct btf *btf) { GElf_Shdr shdr_mem, *shdr; diff --git a/libbtf.h b/libbtf.h index f3c8500..d9e723a 100644 --- a/libbtf.h +++ b/libbtf.h @@ -55,6 +55,8 @@ int32_t btf_elf__add_enum(struct btf_elf *btf, uint32_t name, uint32_t size, int btf_elf__add_enum_val(struct btf_elf *btf, uint32_t name, int32_t value); int32_t btf_elf__add_func_proto(struct btf_elf *btf, struct ftype *ftype, uint32_t type_id_off); +int32_t btf_elf__add_var_type(struct btf_elf *btfe, uint32_t type, uint32_t name_off, + uint32_t linkage, uint32_t type_id_off); void btf_elf__set_strings(struct btf_elf *btf, struct gobuffer *strings); int btf_elf__encode(struct btf_elf *btf, uint8_t flags); diff --git a/pahole.c b/pahole.c index e2a081b..8407db9 100644 --- a/pahole.c +++ b/pahole.c @@ -1084,6 +1084,7 @@ static error_t pahole__options_parser(int key, char *arg, case 'i': find_containers = 1; class_name = arg; break; case 'J': btf_encode = 1; + conf_load.get_addr_info = true; no_bitfield_type_recode = true; break; case 'l': conf.show_first_biggest_size_base_type_member = 1; break; case 'M': conf.show_only_data_members = 1; break; -- 2.27.0.rc2.251.g90737beb825-goog
