// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/*
* BTF-to-C type converter.
*
* Copyright (c) 2019 Facebook
*/
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <linux/err.h>
#include <linux/btf.h>
#include "btf.h"
#include "hashmap.h"
#include "libbpf.h"
#include "libbpf_internal.h"
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;
};
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 __u16 btf_kind_of(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info);
}
static __u16 btf_vlen_of(const struct btf_type *t)
{
return BTF_INFO_VLEN(t->info);
}
static bool btf_kflag_of(const struct btf_type *t)
{
return BTF_INFO_KFLAG(t->info);
}
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);
}
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;
btf_dump__free(d);
return ERR_PTR(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;
btf_dump__free(d);
return ERR_PTR(err);
}
return d;
}
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;
/* type states are lazily allocated, as they might not be needed */
if (!d->type_states) {
d->type_states = calloc(1 + btf__get_nr_types(d->btf),
sizeof(d->type_states[0]));
if (!d->type_states)
return -ENOMEM;
d->cached_names = calloc(1 + btf__get_nr_types(d->btf),
sizeof(d->cached_names[0]));
if (!d->cached_names)
return -ENOMEM;
/* VOID is special */
d->type_states[0].order_state = ORDERED;
d->type_states[0].emit_state = EMITTED;
}
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;
}
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 kind, 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);
kind = btf_kind_of(t);
if (tstate->order_state == ORDERING) {
/* type loop, but resolvable through fwd declaration */
if ((kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION) &&
through_ptr && t->name_off != 0)
return 0;
pr_warning("unsatisfiable type cycle, id:[%u]\n", id);
return -ELOOP;
}
switch (kind) {
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: {
const struct btf_array *a = (void *)(t + 1);
return btf_dump_order_type(d, a->type, through_ptr);
}
case BTF_KIND_STRUCT:
case BTF_KIND_UNION: {
const struct btf_member *m = (void *)(t + 1);
/*
* 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_of(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:
if (t->name_off != 0) {
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 = (void *)(t + 1);
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_of(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_of(t);
if (top_level_def && t->name_off == 0) {
pr_warning("unexpected nameless definition, id:[%u]\n", id);
return;
}
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_warning("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: {
const struct btf_array *a = (void *)(t + 1);
btf_dump_emit_type(d, a->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 = (void *)(t + 1);
__u16 vlen = btf_vlen_of(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 = (void *)(t + 1);
__u16 vlen = btf_vlen_of(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 int btf_align_of(const struct btf *btf, __u32 id)
{
const struct btf_type *t = btf__type_by_id(btf, id);
__u16 kind = btf_kind_of(t);
switch (kind) {
case BTF_KIND_INT:
case BTF_KIND_ENUM:
return min(sizeof(void *), t->size);
case BTF_KIND_PTR:
return sizeof(void *);
case BTF_KIND_TYPEDEF:
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
return btf_align_of(btf, t->type);
case BTF_KIND_ARRAY: {
const struct btf_array *a = (void *)(t + 1);
return btf_align_of(btf, a->type);
}
case BTF_KIND_STRUCT:
case BTF_KIND_UNION: {
const struct btf_member *m = (void *)(t + 1);
__u16 vlen = btf_vlen_of(t);
int i, align = 1;
for (i = 0; i < vlen; i++, m++)
align = max(align, btf_align_of(btf, m->type));
return align;
}
default:
pr_warning("unsupported BTF_KIND:%u\n", btf_kind_of(t));
return 1;
}
}
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;
bool kflag;
align = btf_align_of(btf, id);
/* size of a non-packed struct has to be a multiple of its alignment*/
if (t->size % align)
return true;
m = (void *)(t + 1);
kflag = btf_kflag_of(t);
vlen = btf_vlen_of(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 = kflag ? BTF_MEMBER_BITFIELD_SIZE(m->offset) : 0;
if (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_kind_of(t) == BTF_KIND_STRUCT ? "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 = (void *)(t + 1);
bool kflag = btf_kflag_of(t), is_struct;
int align, i, packed, off = 0;
__u16 vlen = btf_vlen_of(t);
is_struct = btf_kind_of(t) == BTF_KIND_STRUCT;
packed = is_struct ? btf_is_struct_packed(d->btf, id, t) : 0;
align = packed ? 1 : btf_align_of(d->btf, id);
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 = kflag ? BTF_MEMBER_BITFIELD_SIZE(m->offset) : 0;
m_off = kflag ? BTF_MEMBER_BIT_OFFSET(m->offset) : m->offset;
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, ";");
}
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 = (void *)(t+1);
__u16 vlen = btf_vlen_of(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_of(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);
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.
*/
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;
__u16 kind;
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_warning("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);
kind = btf_kind_of(t);
switch (kind) {
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: {
const struct btf_array *a = (void *)(t + 1);
id = a->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_warning("unexpected type in decl chain, kind:%u, id:[%u]\n",
kind, 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_of(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 bool btf_is_mod_kind(const struct btf *btf, __u32 id)
{
const struct btf_type *t = btf__type_by_id(btf, id);
switch (btf_kind_of(t)) {
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
return true;
default:
return false;
}
}
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 (*<fname>), 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_of(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 = (void *)(t + 1);
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];
if (btf_is_mod_kind(d->btf, next_id))
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_t = btf__type_by_id(d->btf, next_id);
multidim = btf_kind_of(next_t) == BTF_KIND_ARRAY;
/* 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 = (void *)(t + 1);
__u16 vlen = btf_vlen_of(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_warning("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);
}
