// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) /* * BTF-to-C type converter. * * Copyright (c) 2019 Facebook */ #include #include #include #include #include #include #include #include "btf.h" #include "hashmap.h" #include "libbpf.h" #include "libbpf_internal.h" /* make sure libbpf doesn't use kernel-only integer typedefs */ #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64 static const char PREFIXES[] = "\t\t\t\t\t\t\t\t\t\t\t\t\t"; static const size_t PREFIX_CNT = sizeof(PREFIXES) - 1; static const char *pfx(int lvl) { return lvl >= PREFIX_CNT ? PREFIXES : &PREFIXES[PREFIX_CNT - lvl]; } enum btf_dump_type_order_state { NOT_ORDERED, ORDERING, ORDERED, }; enum btf_dump_type_emit_state { NOT_EMITTED, EMITTING, EMITTED, }; /* per-type auxiliary state */ struct btf_dump_type_aux_state { /* topological sorting state */ enum btf_dump_type_order_state order_state: 2; /* emitting state used to determine the need for forward declaration */ enum btf_dump_type_emit_state emit_state: 2; /* whether forward declaration was already emitted */ __u8 fwd_emitted: 1; /* whether unique non-duplicate name was already assigned */ __u8 name_resolved: 1; /* whether type is referenced from any other type */ __u8 referenced: 1; }; struct btf_dump { const struct btf *btf; const struct btf_ext *btf_ext; btf_dump_printf_fn_t printf_fn; struct btf_dump_opts opts; /* per-type auxiliary state */ struct btf_dump_type_aux_state *type_states; /* per-type optional cached unique name, must be freed, if present */ const char **cached_names; /* topo-sorted list of dependent type definitions */ __u32 *emit_queue; int emit_queue_cap; int emit_queue_cnt; /* * stack of type declarations (e.g., chain of modifiers, arrays, * funcs, etc) */ __u32 *decl_stack; int decl_stack_cap; int decl_stack_cnt; /* maps struct/union/enum name to a number of name occurrences */ struct hashmap *type_names; /* * maps typedef identifiers and enum value names to a number of such * name occurrences */ struct hashmap *ident_names; }; static size_t str_hash_fn(const void *key, void *ctx) { const char *s = key; size_t h = 0; while (*s) { h = h * 31 + *s; s++; } return h; } static bool str_equal_fn(const void *a, const void *b, void *ctx) { return strcmp(a, b) == 0; } static const char *btf_name_of(const struct btf_dump *d, __u32 name_off) { return btf__name_by_offset(d->btf, name_off); } static void btf_dump_printf(const struct btf_dump *d, const char *fmt, ...) { va_list args; va_start(args, fmt); d->printf_fn(d->opts.ctx, fmt, args); va_end(args); } static int btf_dump_mark_referenced(struct btf_dump *d); struct btf_dump *btf_dump__new(const struct btf *btf, const struct btf_ext *btf_ext, const struct btf_dump_opts *opts, btf_dump_printf_fn_t printf_fn) { struct btf_dump *d; int err; d = calloc(1, sizeof(struct btf_dump)); if (!d) return ERR_PTR(-ENOMEM); d->btf = btf; d->btf_ext = btf_ext; d->printf_fn = printf_fn; d->opts.ctx = opts ? opts->ctx : NULL; d->type_names = hashmap__new(str_hash_fn, str_equal_fn, NULL); if (IS_ERR(d->type_names)) { err = PTR_ERR(d->type_names); d->type_names = NULL; goto err; } d->ident_names = hashmap__new(str_hash_fn, str_equal_fn, NULL); if (IS_ERR(d->ident_names)) { err = PTR_ERR(d->ident_names); d->ident_names = NULL; goto err; } d->type_states = calloc(1 + btf__get_nr_types(d->btf), sizeof(d->type_states[0])); if (!d->type_states) { err = -ENOMEM; goto err; } d->cached_names = calloc(1 + btf__get_nr_types(d->btf), sizeof(d->cached_names[0])); if (!d->cached_names) { err = -ENOMEM; goto err; } /* VOID is special */ d->type_states[0].order_state = ORDERED; d->type_states[0].emit_state = EMITTED; /* eagerly determine referenced types for anon enums */ err = btf_dump_mark_referenced(d); if (err) goto err; return d; err: btf_dump__free(d); return ERR_PTR(err); } void btf_dump__free(struct btf_dump *d) { int i, cnt; if (!d) return; free(d->type_states); if (d->cached_names) { /* any set cached name is owned by us and should be freed */ for (i = 0, cnt = btf__get_nr_types(d->btf); i <= cnt; i++) { if (d->cached_names[i]) free((void *)d->cached_names[i]); } } free(d->cached_names); free(d->emit_queue); free(d->decl_stack); hashmap__free(d->type_names); hashmap__free(d->ident_names); free(d); } static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr); static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id); /* * Dump BTF type in a compilable C syntax, including all the necessary * dependent types, necessary for compilation. If some of the dependent types * were already emitted as part of previous btf_dump__dump_type() invocation * for another type, they won't be emitted again. This API allows callers to * filter out BTF types according to user-defined criterias and emitted only * minimal subset of types, necessary to compile everything. Full struct/union * definitions will still be emitted, even if the only usage is through * pointer and could be satisfied with just a forward declaration. * * Dumping is done in two high-level passes: * 1. Topologically sort type definitions to satisfy C rules of compilation. * 2. Emit type definitions in C syntax. * * Returns 0 on success; <0, otherwise. */ int btf_dump__dump_type(struct btf_dump *d, __u32 id) { int err, i; if (id > btf__get_nr_types(d->btf)) return -EINVAL; d->emit_queue_cnt = 0; err = btf_dump_order_type(d, id, false); if (err < 0) return err; for (i = 0; i < d->emit_queue_cnt; i++) btf_dump_emit_type(d, d->emit_queue[i], 0 /*top-level*/); return 0; } /* * Mark all types that are referenced from any other type. This is used to * determine top-level anonymous enums that need to be emitted as an * independent type declarations. * Anonymous enums come in two flavors: either embedded in a struct's field * definition, in which case they have to be declared inline as part of field * type declaration; or as a top-level anonymous enum, typically used for * declaring global constants. It's impossible to distinguish between two * without knowning whether given enum type was referenced from other type: * top-level anonymous enum won't be referenced by anything, while embedded * one will. */ static int btf_dump_mark_referenced(struct btf_dump *d) { int i, j, n = btf__get_nr_types(d->btf); const struct btf_type *t; __u16 vlen; for (i = 1; i <= n; i++) { t = btf__type_by_id(d->btf, i); vlen = btf_vlen(t); switch (btf_kind(t)) { case BTF_KIND_INT: case BTF_KIND_ENUM: case BTF_KIND_FWD: break; case BTF_KIND_VOLATILE: case BTF_KIND_CONST: case BTF_KIND_RESTRICT: case BTF_KIND_PTR: case BTF_KIND_TYPEDEF: case BTF_KIND_FUNC: case BTF_KIND_VAR: d->type_states[t->type].referenced = 1; break; case BTF_KIND_ARRAY: { const struct btf_array *a = btf_array(t); d->type_states[a->index_type].referenced = 1; d->type_states[a->type].referenced = 1; break; } case BTF_KIND_STRUCT: case BTF_KIND_UNION: { const struct btf_member *m = btf_members(t); for (j = 0; j < vlen; j++, m++) d->type_states[m->type].referenced = 1; break; } case BTF_KIND_FUNC_PROTO: { const struct btf_param *p = btf_params(t); for (j = 0; j < vlen; j++, p++) d->type_states[p->type].referenced = 1; break; } case BTF_KIND_DATASEC: { const struct btf_var_secinfo *v = btf_var_secinfos(t); for (j = 0; j < vlen; j++, v++) d->type_states[v->type].referenced = 1; break; } default: return -EINVAL; } } return 0; } static int btf_dump_add_emit_queue_id(struct btf_dump *d, __u32 id) { __u32 *new_queue; size_t new_cap; if (d->emit_queue_cnt >= d->emit_queue_cap) { new_cap = max(16, d->emit_queue_cap * 3 / 2); new_queue = realloc(d->emit_queue, new_cap * sizeof(new_queue[0])); if (!new_queue) return -ENOMEM; d->emit_queue = new_queue; d->emit_queue_cap = new_cap; } d->emit_queue[d->emit_queue_cnt++] = id; return 0; } /* * Determine order of emitting dependent types and specified type to satisfy * C compilation rules. This is done through topological sorting with an * additional complication which comes from C rules. The main idea for C is * that if some type is "embedded" into a struct/union, it's size needs to be * known at the time of definition of containing type. E.g., for: * * struct A {}; * struct B { struct A x; } * * struct A *HAS* to be defined before struct B, because it's "embedded", * i.e., it is part of struct B layout. But in the following case: * * struct A; * struct B { struct A *x; } * struct A {}; * * it's enough to just have a forward declaration of struct A at the time of * struct B definition, as struct B has a pointer to struct A, so the size of * field x is known without knowing struct A size: it's sizeof(void *). * * Unfortunately, there are some trickier cases we need to handle, e.g.: * * struct A {}; // if this was forward-declaration: compilation error * struct B { * struct { // anonymous struct * struct A y; * } *x; * }; * * In this case, struct B's field x is a pointer, so it's size is known * regardless of the size of (anonymous) struct it points to. But because this * struct is anonymous and thus defined inline inside struct B, *and* it * embeds struct A, compiler requires full definition of struct A to be known * before struct B can be defined. This creates a transitive dependency * between struct A and struct B. If struct A was forward-declared before * struct B definition and fully defined after struct B definition, that would * trigger compilation error. * * All this means that while we are doing topological sorting on BTF type * graph, we need to determine relationships between different types (graph * nodes): * - weak link (relationship) between X and Y, if Y *CAN* be * forward-declared at the point of X definition; * - strong link, if Y *HAS* to be fully-defined before X can be defined. * * The rule is as follows. Given a chain of BTF types from X to Y, if there is * BTF_KIND_PTR type in the chain and at least one non-anonymous type * Z (excluding X, including Y), then link is weak. Otherwise, it's strong. * Weak/strong relationship is determined recursively during DFS traversal and * is returned as a result from btf_dump_order_type(). * * btf_dump_order_type() is trying to avoid unnecessary forward declarations, * but it is not guaranteeing that no extraneous forward declarations will be * emitted. * * To avoid extra work, algorithm marks some of BTF types as ORDERED, when * it's done with them, but not for all (e.g., VOLATILE, CONST, RESTRICT, * ARRAY, FUNC_PROTO), as weak/strong semantics for those depends on the * entire graph path, so depending where from one came to that BTF type, it * might cause weak or strong ordering. For types like STRUCT/UNION/INT/ENUM, * once they are processed, there is no need to do it again, so they are * marked as ORDERED. We can mark PTR as ORDERED as well, as it semi-forces * weak link, unless subsequent referenced STRUCT/UNION/ENUM is anonymous. But * in any case, once those are processed, no need to do it again, as the * result won't change. * * Returns: * - 1, if type is part of strong link (so there is strong topological * ordering requirements); * - 0, if type is part of weak link (so can be satisfied through forward * declaration); * - <0, on error (e.g., unsatisfiable type loop detected). */ static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr) { /* * Order state is used to detect strong link cycles, but only for BTF * kinds that are or could be an independent definition (i.e., * stand-alone fwd decl, enum, typedef, struct, union). Ptrs, arrays, * func_protos, modifiers are just means to get to these definitions. * Int/void don't need definitions, they are assumed to be always * properly defined. We also ignore datasec, var, and funcs for now. * So for all non-defining kinds, we never even set ordering state, * for defining kinds we set ORDERING and subsequently ORDERED if it * forms a strong link. */ struct btf_dump_type_aux_state *tstate = &d->type_states[id]; const struct btf_type *t; __u16 vlen; int err, i; /* return true, letting typedefs know that it's ok to be emitted */ if (tstate->order_state == ORDERED) return 1; t = btf__type_by_id(d->btf, id); if (tstate->order_state == ORDERING) { /* type loop, but resolvable through fwd declaration */ if (btf_is_composite(t) && through_ptr && t->name_off != 0) return 0; pr_warn("unsatisfiable type cycle, id:[%u]\n", id); return -ELOOP; } switch (btf_kind(t)) { case BTF_KIND_INT: tstate->order_state = ORDERED; return 0; case BTF_KIND_PTR: err = btf_dump_order_type(d, t->type, true); tstate->order_state = ORDERED; return err; case BTF_KIND_ARRAY: return btf_dump_order_type(d, btf_array(t)->type, through_ptr); case BTF_KIND_STRUCT: case BTF_KIND_UNION: { const struct btf_member *m = btf_members(t); /* * struct/union is part of strong link, only if it's embedded * (so no ptr in a path) or it's anonymous (so has to be * defined inline, even if declared through ptr) */ if (through_ptr && t->name_off != 0) return 0; tstate->order_state = ORDERING; vlen = btf_vlen(t); for (i = 0; i < vlen; i++, m++) { err = btf_dump_order_type(d, m->type, false); if (err < 0) return err; } if (t->name_off != 0) { err = btf_dump_add_emit_queue_id(d, id); if (err < 0) return err; } tstate->order_state = ORDERED; return 1; } case BTF_KIND_ENUM: case BTF_KIND_FWD: /* * non-anonymous or non-referenced enums are top-level * declarations and should be emitted. Same logic can be * applied to FWDs, it won't hurt anyways. */ if (t->name_off != 0 || !tstate->referenced) { err = btf_dump_add_emit_queue_id(d, id); if (err) return err; } tstate->order_state = ORDERED; return 1; case BTF_KIND_TYPEDEF: { int is_strong; is_strong = btf_dump_order_type(d, t->type, through_ptr); if (is_strong < 0) return is_strong; /* typedef is similar to struct/union w.r.t. fwd-decls */ if (through_ptr && !is_strong) return 0; /* typedef is always a named definition */ err = btf_dump_add_emit_queue_id(d, id); if (err) return err; d->type_states[id].order_state = ORDERED; return 1; } case BTF_KIND_VOLATILE: case BTF_KIND_CONST: case BTF_KIND_RESTRICT: return btf_dump_order_type(d, t->type, through_ptr); case BTF_KIND_FUNC_PROTO: { const struct btf_param *p = btf_params(t); bool is_strong; err = btf_dump_order_type(d, t->type, through_ptr); if (err < 0) return err; is_strong = err > 0; vlen = btf_vlen(t); for (i = 0; i < vlen; i++, p++) { err = btf_dump_order_type(d, p->type, through_ptr); if (err < 0) return err; if (err > 0) is_strong = true; } return is_strong; } case BTF_KIND_FUNC: case BTF_KIND_VAR: case BTF_KIND_DATASEC: d->type_states[id].order_state = ORDERED; return 0; default: return -EINVAL; } } static void btf_dump_emit_struct_fwd(struct btf_dump *d, __u32 id, const struct btf_type *t); static void btf_dump_emit_struct_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl); static void btf_dump_emit_enum_fwd(struct btf_dump *d, __u32 id, const struct btf_type *t); static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl); static void btf_dump_emit_fwd_def(struct btf_dump *d, __u32 id, const struct btf_type *t); static void btf_dump_emit_typedef_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl); /* a local view into a shared stack */ struct id_stack { const __u32 *ids; int cnt; }; static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id, const char *fname, int lvl); static void btf_dump_emit_type_chain(struct btf_dump *d, struct id_stack *decl_stack, const char *fname, int lvl); static const char *btf_dump_type_name(struct btf_dump *d, __u32 id); static const char *btf_dump_ident_name(struct btf_dump *d, __u32 id); static size_t btf_dump_name_dups(struct btf_dump *d, struct hashmap *name_map, const char *orig_name); static bool btf_dump_is_blacklisted(struct btf_dump *d, __u32 id) { const struct btf_type *t = btf__type_by_id(d->btf, id); /* __builtin_va_list is a compiler built-in, which causes compilation * errors, when compiling w/ different compiler, then used to compile * original code (e.g., GCC to compile kernel, Clang to use generated * C header from BTF). As it is built-in, it should be already defined * properly internally in compiler. */ if (t->name_off == 0) return false; return strcmp(btf_name_of(d, t->name_off), "__builtin_va_list") == 0; } /* * Emit C-syntax definitions of types from chains of BTF types. * * High-level handling of determining necessary forward declarations are handled * by btf_dump_emit_type() itself, but all nitty-gritty details of emitting type * declarations/definitions in C syntax are handled by a combo of * btf_dump_emit_type_decl()/btf_dump_emit_type_chain() w/ delegation to * corresponding btf_dump_emit_*_{def,fwd}() functions. * * We also keep track of "containing struct/union type ID" to determine when * we reference it from inside and thus can avoid emitting unnecessary forward * declaration. * * This algorithm is designed in such a way, that even if some error occurs * (either technical, e.g., out of memory, or logical, i.e., malformed BTF * that doesn't comply to C rules completely), algorithm will try to proceed * and produce as much meaningful output as possible. */ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id) { struct btf_dump_type_aux_state *tstate = &d->type_states[id]; bool top_level_def = cont_id == 0; const struct btf_type *t; __u16 kind; if (tstate->emit_state == EMITTED) return; t = btf__type_by_id(d->btf, id); kind = btf_kind(t); if (tstate->emit_state == EMITTING) { if (tstate->fwd_emitted) return; switch (kind) { case BTF_KIND_STRUCT: case BTF_KIND_UNION: /* * if we are referencing a struct/union that we are * part of - then no need for fwd declaration */ if (id == cont_id) return; if (t->name_off == 0) { pr_warn("anonymous struct/union loop, id:[%u]\n", id); return; } btf_dump_emit_struct_fwd(d, id, t); btf_dump_printf(d, ";\n\n"); tstate->fwd_emitted = 1; break; case BTF_KIND_TYPEDEF: /* * for typedef fwd_emitted means typedef definition * was emitted, but it can be used only for "weak" * references through pointer only, not for embedding */ if (!btf_dump_is_blacklisted(d, id)) { btf_dump_emit_typedef_def(d, id, t, 0); btf_dump_printf(d, ";\n\n"); }; tstate->fwd_emitted = 1; break; default: break; } return; } switch (kind) { case BTF_KIND_INT: tstate->emit_state = EMITTED; break; case BTF_KIND_ENUM: if (top_level_def) { btf_dump_emit_enum_def(d, id, t, 0); btf_dump_printf(d, ";\n\n"); } tstate->emit_state = EMITTED; break; case BTF_KIND_PTR: case BTF_KIND_VOLATILE: case BTF_KIND_CONST: case BTF_KIND_RESTRICT: btf_dump_emit_type(d, t->type, cont_id); break; case BTF_KIND_ARRAY: btf_dump_emit_type(d, btf_array(t)->type, cont_id); break; case BTF_KIND_FWD: btf_dump_emit_fwd_def(d, id, t); btf_dump_printf(d, ";\n\n"); tstate->emit_state = EMITTED; break; case BTF_KIND_TYPEDEF: tstate->emit_state = EMITTING; btf_dump_emit_type(d, t->type, id); /* * typedef can server as both definition and forward * declaration; at this stage someone depends on * typedef as a forward declaration (refers to it * through pointer), so unless we already did it, * emit typedef as a forward declaration */ if (!tstate->fwd_emitted && !btf_dump_is_blacklisted(d, id)) { btf_dump_emit_typedef_def(d, id, t, 0); btf_dump_printf(d, ";\n\n"); } tstate->emit_state = EMITTED; break; case BTF_KIND_STRUCT: case BTF_KIND_UNION: tstate->emit_state = EMITTING; /* if it's a top-level struct/union definition or struct/union * is anonymous, then in C we'll be emitting all fields and * their types (as opposed to just `struct X`), so we need to * make sure that all types, referenced from struct/union * members have necessary forward-declarations, where * applicable */ if (top_level_def || t->name_off == 0) { const struct btf_member *m = btf_members(t); __u16 vlen = btf_vlen(t); int i, new_cont_id; new_cont_id = t->name_off == 0 ? cont_id : id; for (i = 0; i < vlen; i++, m++) btf_dump_emit_type(d, m->type, new_cont_id); } else if (!tstate->fwd_emitted && id != cont_id) { btf_dump_emit_struct_fwd(d, id, t); btf_dump_printf(d, ";\n\n"); tstate->fwd_emitted = 1; } if (top_level_def) { btf_dump_emit_struct_def(d, id, t, 0); btf_dump_printf(d, ";\n\n"); tstate->emit_state = EMITTED; } else { tstate->emit_state = NOT_EMITTED; } break; case BTF_KIND_FUNC_PROTO: { const struct btf_param *p = btf_params(t); __u16 vlen = btf_vlen(t); int i; btf_dump_emit_type(d, t->type, cont_id); for (i = 0; i < vlen; i++, p++) btf_dump_emit_type(d, p->type, cont_id); break; } default: break; } } static bool btf_is_struct_packed(const struct btf *btf, __u32 id, const struct btf_type *t) { const struct btf_member *m; int align, i, bit_sz; __u16 vlen; align = btf__align_of(btf, id); /* size of a non-packed struct has to be a multiple of its alignment*/ if (align && t->size % align) return true; m = btf_members(t); vlen = btf_vlen(t); /* all non-bitfield fields have to be naturally aligned */ for (i = 0; i < vlen; i++, m++) { align = btf__align_of(btf, m->type); bit_sz = btf_member_bitfield_size(t, i); if (align && bit_sz == 0 && m->offset % (8 * align) != 0) return true; } /* * if original struct was marked as packed, but its layout is * naturally aligned, we'll detect that it's not packed */ return false; } static int chip_away_bits(int total, int at_most) { return total % at_most ? : at_most; } static void btf_dump_emit_bit_padding(const struct btf_dump *d, int cur_off, int m_off, int m_bit_sz, int align, int lvl) { int off_diff = m_off - cur_off; int ptr_bits = sizeof(void *) * 8; if (off_diff <= 0) /* no gap */ return; if (m_bit_sz == 0 && off_diff < align * 8) /* natural padding will take care of a gap */ return; while (off_diff > 0) { const char *pad_type; int pad_bits; if (ptr_bits > 32 && off_diff > 32) { pad_type = "long"; pad_bits = chip_away_bits(off_diff, ptr_bits); } else if (off_diff > 16) { pad_type = "int"; pad_bits = chip_away_bits(off_diff, 32); } else if (off_diff > 8) { pad_type = "short"; pad_bits = chip_away_bits(off_diff, 16); } else { pad_type = "char"; pad_bits = chip_away_bits(off_diff, 8); } btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, pad_bits); off_diff -= pad_bits; } } static void btf_dump_emit_struct_fwd(struct btf_dump *d, __u32 id, const struct btf_type *t) { btf_dump_printf(d, "%s %s", btf_is_struct(t) ? "struct" : "union", btf_dump_type_name(d, id)); } static void btf_dump_emit_struct_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl) { const struct btf_member *m = btf_members(t); bool is_struct = btf_is_struct(t); int align, i, packed, off = 0; __u16 vlen = btf_vlen(t); packed = is_struct ? btf_is_struct_packed(d->btf, id, t) : 0; btf_dump_printf(d, "%s%s%s {", is_struct ? "struct" : "union", t->name_off ? " " : "", btf_dump_type_name(d, id)); for (i = 0; i < vlen; i++, m++) { const char *fname; int m_off, m_sz; fname = btf_name_of(d, m->name_off); m_sz = btf_member_bitfield_size(t, i); m_off = btf_member_bit_offset(t, i); align = packed ? 1 : btf__align_of(d->btf, m->type); btf_dump_emit_bit_padding(d, off, m_off, m_sz, align, lvl + 1); btf_dump_printf(d, "\n%s", pfx(lvl + 1)); btf_dump_emit_type_decl(d, m->type, fname, lvl + 1); if (m_sz) { btf_dump_printf(d, ": %d", m_sz); off = m_off + m_sz; } else { m_sz = max(0, btf__resolve_size(d->btf, m->type)); off = m_off + m_sz * 8; } btf_dump_printf(d, ";"); } /* pad at the end, if necessary */ if (is_struct) { align = packed ? 1 : btf__align_of(d->btf, id); btf_dump_emit_bit_padding(d, off, t->size * 8, 0, align, lvl + 1); } if (vlen) btf_dump_printf(d, "\n"); btf_dump_printf(d, "%s}", pfx(lvl)); if (packed) btf_dump_printf(d, " __attribute__((packed))"); } static void btf_dump_emit_enum_fwd(struct btf_dump *d, __u32 id, const struct btf_type *t) { btf_dump_printf(d, "enum %s", btf_dump_type_name(d, id)); } static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl) { const struct btf_enum *v = btf_enum(t); __u16 vlen = btf_vlen(t); const char *name; size_t dup_cnt; int i; btf_dump_printf(d, "enum%s%s", t->name_off ? " " : "", btf_dump_type_name(d, id)); if (vlen) { btf_dump_printf(d, " {"); for (i = 0; i < vlen; i++, v++) { name = btf_name_of(d, v->name_off); /* enumerators share namespace with typedef idents */ dup_cnt = btf_dump_name_dups(d, d->ident_names, name); if (dup_cnt > 1) { btf_dump_printf(d, "\n%s%s___%zu = %d,", pfx(lvl + 1), name, dup_cnt, (__s32)v->val); } else { btf_dump_printf(d, "\n%s%s = %d,", pfx(lvl + 1), name, (__s32)v->val); } } btf_dump_printf(d, "\n%s}", pfx(lvl)); } } static void btf_dump_emit_fwd_def(struct btf_dump *d, __u32 id, const struct btf_type *t) { const char *name = btf_dump_type_name(d, id); if (btf_kflag(t)) btf_dump_printf(d, "union %s", name); else btf_dump_printf(d, "struct %s", name); } static void btf_dump_emit_typedef_def(struct btf_dump *d, __u32 id, const struct btf_type *t, int lvl) { const char *name = btf_dump_ident_name(d, id); /* * Old GCC versions are emitting invalid typedef for __gnuc_va_list * pointing to VOID. This generates warnings from btf_dump() and * results in uncompilable header file, so we are fixing it up here * with valid typedef into __builtin_va_list. */ if (t->type == 0 && strcmp(name, "__gnuc_va_list") == 0) { btf_dump_printf(d, "typedef __builtin_va_list __gnuc_va_list"); return; } btf_dump_printf(d, "typedef "); btf_dump_emit_type_decl(d, t->type, name, lvl); } static int btf_dump_push_decl_stack_id(struct btf_dump *d, __u32 id) { __u32 *new_stack; size_t new_cap; if (d->decl_stack_cnt >= d->decl_stack_cap) { new_cap = max(16, d->decl_stack_cap * 3 / 2); new_stack = realloc(d->decl_stack, new_cap * sizeof(new_stack[0])); if (!new_stack) return -ENOMEM; d->decl_stack = new_stack; d->decl_stack_cap = new_cap; } d->decl_stack[d->decl_stack_cnt++] = id; return 0; } /* * Emit type declaration (e.g., field type declaration in a struct or argument * declaration in function prototype) in correct C syntax. * * For most types it's trivial, but there are few quirky type declaration * cases worth mentioning: * - function prototypes (especially nesting of function prototypes); * - arrays; * - const/volatile/restrict for pointers vs other types. * * For a good discussion of *PARSING* C syntax (as a human), see * Peter van der Linden's "Expert C Programming: Deep C Secrets", * Ch.3 "Unscrambling Declarations in C". * * It won't help with BTF to C conversion much, though, as it's an opposite * problem. So we came up with this algorithm in reverse to van der Linden's * parsing algorithm. It goes from structured BTF representation of type * declaration to a valid compilable C syntax. * * For instance, consider this C typedef: * typedef const int * const * arr[10] arr_t; * It will be represented in BTF with this chain of BTF types: * [typedef] -> [array] -> [ptr] -> [const] -> [ptr] -> [const] -> [int] * * Notice how [const] modifier always goes before type it modifies in BTF type * graph, but in C syntax, const/volatile/restrict modifiers are written to * the right of pointers, but to the left of other types. There are also other * quirks, like function pointers, arrays of them, functions returning other * functions, etc. * * We handle that by pushing all the types to a stack, until we hit "terminal" * type (int/enum/struct/union/fwd). Then depending on the kind of a type on * top of a stack, modifiers are handled differently. Array/function pointers * have also wildly different syntax and how nesting of them are done. See * code for authoritative definition. * * To avoid allocating new stack for each independent chain of BTF types, we * share one bigger stack, with each chain working only on its own local view * of a stack frame. Some care is required to "pop" stack frames after * processing type declaration chain. */ int btf_dump__emit_type_decl(struct btf_dump *d, __u32 id, const struct btf_dump_emit_type_decl_opts *opts) { const char *fname; int lvl; if (!OPTS_VALID(opts, btf_dump_emit_type_decl_opts)) return -EINVAL; fname = OPTS_GET(opts, field_name, NULL); lvl = OPTS_GET(opts, indent_level, 0); btf_dump_emit_type_decl(d, id, fname, lvl); return 0; } static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id, const char *fname, int lvl) { struct id_stack decl_stack; const struct btf_type *t; int err, stack_start; stack_start = d->decl_stack_cnt; for (;;) { err = btf_dump_push_decl_stack_id(d, id); if (err < 0) { /* * if we don't have enough memory for entire type decl * chain, restore stack, emit warning, and try to * proceed nevertheless */ pr_warn("not enough memory for decl stack:%d", err); d->decl_stack_cnt = stack_start; return; } /* VOID */ if (id == 0) break; t = btf__type_by_id(d->btf, id); switch (btf_kind(t)) { case BTF_KIND_PTR: case BTF_KIND_VOLATILE: case BTF_KIND_CONST: case BTF_KIND_RESTRICT: case BTF_KIND_FUNC_PROTO: id = t->type; break; case BTF_KIND_ARRAY: id = btf_array(t)->type; break; case BTF_KIND_INT: case BTF_KIND_ENUM: case BTF_KIND_FWD: case BTF_KIND_STRUCT: case BTF_KIND_UNION: case BTF_KIND_TYPEDEF: goto done; default: pr_warn("unexpected type in decl chain, kind:%u, id:[%u]\n", btf_kind(t), id); goto done; } } done: /* * We might be inside a chain of declarations (e.g., array of function * pointers returning anonymous (so inlined) structs, having another * array field). Each of those needs its own "stack frame" to handle * emitting of declarations. Those stack frames are non-overlapping * portions of shared btf_dump->decl_stack. To make it a bit nicer to * handle this set of nested stacks, we create a view corresponding to * our own "stack frame" and work with it as an independent stack. * We'll need to clean up after emit_type_chain() returns, though. */ decl_stack.ids = d->decl_stack + stack_start; decl_stack.cnt = d->decl_stack_cnt - stack_start; btf_dump_emit_type_chain(d, &decl_stack, fname, lvl); /* * emit_type_chain() guarantees that it will pop its entire decl_stack * frame before returning. But it works with a read-only view into * decl_stack, so it doesn't actually pop anything from the * perspective of shared btf_dump->decl_stack, per se. We need to * reset decl_stack state to how it was before us to avoid it growing * all the time. */ d->decl_stack_cnt = stack_start; } static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack) { const struct btf_type *t; __u32 id; while (decl_stack->cnt) { id = decl_stack->ids[decl_stack->cnt - 1]; t = btf__type_by_id(d->btf, id); switch (btf_kind(t)) { case BTF_KIND_VOLATILE: btf_dump_printf(d, "volatile "); break; case BTF_KIND_CONST: btf_dump_printf(d, "const "); break; case BTF_KIND_RESTRICT: btf_dump_printf(d, "restrict "); break; default: return; } decl_stack->cnt--; } } static void btf_dump_emit_name(const struct btf_dump *d, const char *name, bool last_was_ptr) { bool separate = name[0] && !last_was_ptr; btf_dump_printf(d, "%s%s", separate ? " " : "", name); } static void btf_dump_emit_type_chain(struct btf_dump *d, struct id_stack *decls, const char *fname, int lvl) { /* * last_was_ptr is used to determine if we need to separate pointer * asterisk (*) from previous part of type signature with space, so * that we get `int ***`, instead of `int * * *`. We default to true * for cases where we have single pointer in a chain. E.g., in ptr -> * func_proto case. func_proto will start a new emit_type_chain call * with just ptr, which should be emitted as (*) or (*), so we * don't want to prepend space for that last pointer. */ bool last_was_ptr = true; const struct btf_type *t; const char *name; __u16 kind; __u32 id; while (decls->cnt) { id = decls->ids[--decls->cnt]; if (id == 0) { /* VOID is a special snowflake */ btf_dump_emit_mods(d, decls); btf_dump_printf(d, "void"); last_was_ptr = false; continue; } t = btf__type_by_id(d->btf, id); kind = btf_kind(t); switch (kind) { case BTF_KIND_INT: btf_dump_emit_mods(d, decls); name = btf_name_of(d, t->name_off); btf_dump_printf(d, "%s", name); break; case BTF_KIND_STRUCT: case BTF_KIND_UNION: btf_dump_emit_mods(d, decls); /* inline anonymous struct/union */ if (t->name_off == 0) btf_dump_emit_struct_def(d, id, t, lvl); else btf_dump_emit_struct_fwd(d, id, t); break; case BTF_KIND_ENUM: btf_dump_emit_mods(d, decls); /* inline anonymous enum */ if (t->name_off == 0) btf_dump_emit_enum_def(d, id, t, lvl); else btf_dump_emit_enum_fwd(d, id, t); break; case BTF_KIND_FWD: btf_dump_emit_mods(d, decls); btf_dump_emit_fwd_def(d, id, t); break; case BTF_KIND_TYPEDEF: btf_dump_emit_mods(d, decls); btf_dump_printf(d, "%s", btf_dump_ident_name(d, id)); break; case BTF_KIND_PTR: btf_dump_printf(d, "%s", last_was_ptr ? "*" : " *"); break; case BTF_KIND_VOLATILE: btf_dump_printf(d, " volatile"); break; case BTF_KIND_CONST: btf_dump_printf(d, " const"); break; case BTF_KIND_RESTRICT: btf_dump_printf(d, " restrict"); break; case BTF_KIND_ARRAY: { const struct btf_array *a = btf_array(t); const struct btf_type *next_t; __u32 next_id; bool multidim; /* * GCC has a bug * (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8354) * which causes it to emit extra const/volatile * modifiers for an array, if array's element type has * const/volatile modifiers. Clang doesn't do that. * In general, it doesn't seem very meaningful to have * a const/volatile modifier for array, so we are * going to silently skip them here. */ while (decls->cnt) { next_id = decls->ids[decls->cnt - 1]; next_t = btf__type_by_id(d->btf, next_id); if (btf_is_mod(next_t)) decls->cnt--; else break; } if (decls->cnt == 0) { btf_dump_emit_name(d, fname, last_was_ptr); btf_dump_printf(d, "[%u]", a->nelems); return; } next_id = decls->ids[decls->cnt - 1]; next_t = btf__type_by_id(d->btf, next_id); multidim = btf_is_array(next_t); /* we need space if we have named non-pointer */ if (fname[0] && !last_was_ptr) btf_dump_printf(d, " "); /* no parentheses for multi-dimensional array */ if (!multidim) btf_dump_printf(d, "("); btf_dump_emit_type_chain(d, decls, fname, lvl); if (!multidim) btf_dump_printf(d, ")"); btf_dump_printf(d, "[%u]", a->nelems); return; } case BTF_KIND_FUNC_PROTO: { const struct btf_param *p = btf_params(t); __u16 vlen = btf_vlen(t); int i; btf_dump_emit_mods(d, decls); if (decls->cnt) { btf_dump_printf(d, " ("); btf_dump_emit_type_chain(d, decls, fname, lvl); btf_dump_printf(d, ")"); } else { btf_dump_emit_name(d, fname, last_was_ptr); } btf_dump_printf(d, "("); /* * Clang for BPF target generates func_proto with no * args as a func_proto with a single void arg (e.g., * `int (*f)(void)` vs just `int (*f)()`). We are * going to pretend there are no args for such case. */ if (vlen == 1 && p->type == 0) { btf_dump_printf(d, ")"); return; } for (i = 0; i < vlen; i++, p++) { if (i > 0) btf_dump_printf(d, ", "); /* last arg of type void is vararg */ if (i == vlen - 1 && p->type == 0) { btf_dump_printf(d, "..."); break; } name = btf_name_of(d, p->name_off); btf_dump_emit_type_decl(d, p->type, name, lvl); } btf_dump_printf(d, ")"); return; } default: pr_warn("unexpected type in decl chain, kind:%u, id:[%u]\n", kind, id); return; } last_was_ptr = kind == BTF_KIND_PTR; } btf_dump_emit_name(d, fname, last_was_ptr); } /* return number of duplicates (occurrences) of a given name */ static size_t btf_dump_name_dups(struct btf_dump *d, struct hashmap *name_map, const char *orig_name) { size_t dup_cnt = 0; hashmap__find(name_map, orig_name, (void **)&dup_cnt); dup_cnt++; hashmap__set(name_map, orig_name, (void *)dup_cnt, NULL, NULL); return dup_cnt; } static const char *btf_dump_resolve_name(struct btf_dump *d, __u32 id, struct hashmap *name_map) { struct btf_dump_type_aux_state *s = &d->type_states[id]; const struct btf_type *t = btf__type_by_id(d->btf, id); const char *orig_name = btf_name_of(d, t->name_off); const char **cached_name = &d->cached_names[id]; size_t dup_cnt; if (t->name_off == 0) return ""; if (s->name_resolved) return *cached_name ? *cached_name : orig_name; dup_cnt = btf_dump_name_dups(d, name_map, orig_name); if (dup_cnt > 1) { const size_t max_len = 256; char new_name[max_len]; snprintf(new_name, max_len, "%s___%zu", orig_name, dup_cnt); *cached_name = strdup(new_name); } s->name_resolved = 1; return *cached_name ? *cached_name : orig_name; } static const char *btf_dump_type_name(struct btf_dump *d, __u32 id) { return btf_dump_resolve_name(d, id, d->type_names); } static const char *btf_dump_ident_name(struct btf_dump *d, __u32 id) { return btf_dump_resolve_name(d, id, d->ident_names); }