main.c

// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

/*
 * resolve_btfids scans ELF object for .BTF_ids section and resolves
 * its symbols with BTF ID values.
 *
 * Each symbol points to 4 bytes data and is expected to have
 * following name syntax:
 *
 * __BTF_ID__<type>__<symbol>[__<id>]
 *
 * type is:
 *
 *   func    - lookup BTF_KIND_FUNC symbol with <symbol> name
 *             and store its ID into the data:
 *
 *             __BTF_ID__func__vfs_close__1:
 *             .zero 4
 *
 *   struct  - lookup BTF_KIND_STRUCT symbol with <symbol> name
 *             and store its ID into the data:
 *
 *             __BTF_ID__struct__sk_buff__1:
 *             .zero 4
 *
 *   union   - lookup BTF_KIND_UNION symbol with <symbol> name
 *             and store its ID into the data:
 *
 *             __BTF_ID__union__thread_union__1:
 *             .zero 4
 *
 *   typedef - lookup BTF_KIND_TYPEDEF symbol with <symbol> name
 *             and store its ID into the data:
 *
 *             __BTF_ID__typedef__pid_t__1:
 *             .zero 4
 *
 *   set     - store symbol size into first 4 bytes and sort following
 *             ID list
 *
 *             __BTF_ID__set__list:
 *             .zero 4
 *             list:
 *             __BTF_ID__func__vfs_getattr__3:
 *             .zero 4
 *             __BTF_ID__func__vfs_fallocate__4:
 *             .zero 4
 *
 *   set8    - store symbol size into first 4 bytes and sort following
 *             ID list
 *
 *             __BTF_ID__set8__list:
 *             .zero 8
 *             list:
 *             __BTF_ID__func__vfs_getattr__3:
 *             .zero 4
 *	       .word (1 << 0) | (1 << 2)
 *             __BTF_ID__func__vfs_fallocate__5:
 *             .zero 4
 *	       .word (1 << 3) | (1 << 1) | (1 << 2)
 */

#define  _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <libelf.h>
#include <gelf.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/btf_ids.h>
#include <linux/kallsyms.h>
#include <linux/rbtree.h>
#include <linux/zalloc.h>
#include <linux/err.h>
#include <linux/limits.h>
#include <bpf/btf.h>
#include <bpf/libbpf.h>
#include <subcmd/parse-options.h>

#define BTF_IDS_SECTION	".BTF_ids"
#define BTF_ID_PREFIX	"__BTF_ID__"

#define BTF_STRUCT	"struct"
#define BTF_UNION	"union"
#define BTF_TYPEDEF	"typedef"
#define BTF_FUNC	"func"
#define BTF_SET		"set"
#define BTF_SET8	"set8"

#define ADDR_CNT	100

#if __BYTE_ORDER == __LITTLE_ENDIAN
# define ELFDATANATIVE	ELFDATA2LSB
#elif __BYTE_ORDER == __BIG_ENDIAN
# define ELFDATANATIVE	ELFDATA2MSB
#else
# error "Unknown machine endianness!"
#endif

enum btf_id_kind {
	BTF_ID_KIND_NONE,
	BTF_ID_KIND_SYM,
	BTF_ID_KIND_SET,
	BTF_ID_KIND_SET8
};

struct btf_id {
	struct rb_node	 rb_node;
	char		*name;
	union {
		int	 id;
		int	 cnt;
	};
	enum btf_id_kind kind;
	int		 addr_cnt;
	Elf64_Addr	 addr[ADDR_CNT];
};

struct object {
	const char *path;
	const char *btf_path;
	const char *base_btf_path;

	struct btf *btf;
	struct btf *base_btf;
	bool distill_base;

	struct {
		int		 fd;
		Elf		*elf;
		Elf_Data	*symbols;
		Elf_Data	*idlist;
		int		 symbols_shndx;
		int		 idlist_shndx;
		size_t		 strtabidx;
		unsigned long	 idlist_addr;
		int		 encoding;
	} efile;

	struct rb_root	sets;
	struct rb_root	structs;
	struct rb_root	unions;
	struct rb_root	typedefs;
	struct rb_root	funcs;

	int nr_funcs;
	int nr_structs;
	int nr_unions;
	int nr_typedefs;
};

#define KF_IMPLICIT_ARGS (1 << 16)
#define KF_IMPL_SUFFIX "_impl"

struct kfunc {
	const char *name;
	u32 btf_id;
	u32 flags;
};

struct btf2btf_context {
	struct btf *btf;
	u32 *decl_tags;
	u32 nr_decl_tags;
	u32 max_decl_tags;
	struct kfunc *kfuncs;
	u32 nr_kfuncs;
	u32 max_kfuncs;
};

static int verbose;
static int warnings;

static int eprintf(int level, int var, const char *fmt, ...)
{
	va_list args;
	int ret = 0;

	if (var >= level) {
		va_start(args, fmt);
		ret = vfprintf(stderr, fmt, args);
		va_end(args);
	}
	return ret;
}

#ifndef pr_fmt
#define pr_fmt(fmt) fmt
#endif

#define pr_debug(fmt, ...) \
	eprintf(1, verbose, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debugN(n, fmt, ...) \
	eprintf(n, verbose, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_err(fmt, ...) \
	eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
#define pr_info(fmt, ...) \
	eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)

static bool is_btf_id(const char *name)
{
	return name && !strncmp(name, BTF_ID_PREFIX, sizeof(BTF_ID_PREFIX) - 1);
}

static struct btf_id *btf_id__find(struct rb_root *root, const char *name)
{
	struct rb_node *p = root->rb_node;
	struct btf_id *id;
	int cmp;

	while (p) {
		id = rb_entry(p, struct btf_id, rb_node);
		cmp = strcmp(id->name, name);
		if (cmp < 0)
			p = p->rb_left;
		else if (cmp > 0)
			p = p->rb_right;
		else
			return id;
	}
	return NULL;
}

static struct btf_id *__btf_id__add(struct rb_root *root,
				    char *name,
				    enum btf_id_kind kind,
				    bool unique)
{
	struct rb_node **p = &root->rb_node;
	struct rb_node *parent = NULL;
	struct btf_id *id;
	int cmp;

	while (*p != NULL) {
		parent = *p;
		id = rb_entry(parent, struct btf_id, rb_node);
		cmp = strcmp(id->name, name);
		if (cmp < 0)
			p = &(*p)->rb_left;
		else if (cmp > 0)
			p = &(*p)->rb_right;
		else
			return unique ? NULL : id;
	}

	id = zalloc(sizeof(*id));
	if (id) {
		pr_debug("adding symbol %s\n", name);
		id->name = name;
		id->kind = kind;
		rb_link_node(&id->rb_node, parent, p);
		rb_insert_color(&id->rb_node, root);
	}
	return id;
}

static inline struct btf_id *btf_id__add(struct rb_root *root, char *name, enum btf_id_kind kind)
{
	return __btf_id__add(root, name, kind, false);
}

static inline struct btf_id *btf_id__add_unique(struct rb_root *root, char *name, enum btf_id_kind kind)
{
	return __btf_id__add(root, name, kind, true);
}

static char *get_id(const char *prefix_end)
{
	/*
	 * __BTF_ID__func__vfs_truncate__0
	 * prefix_end =  ^
	 * pos        =    ^
	 */
	int len = strlen(prefix_end);
	int pos = sizeof("__") - 1;
	char *p, *id;

	if (pos >= len)
		return NULL;

	id = strdup(prefix_end + pos);
	if (id) {
		/*
		 * __BTF_ID__func__vfs_truncate__0
		 * id =            ^
		 *
		 * cut the unique id part
		 */
		p = strrchr(id, '_');
		p--;
		if (*p != '_') {
			free(id);
			return NULL;
		}
		*p = '\0';
	}
	return id;
}

static struct btf_id *add_set(struct object *obj, char *name, enum btf_id_kind kind)
{
	int len = strlen(name);
	int prefixlen;
	char *id;

	/*
	 * __BTF_ID__set__name
	 * name =    ^
	 * id   =         ^
	 */
	switch (kind) {
	case BTF_ID_KIND_SET:
		prefixlen = sizeof(BTF_SET "__") - 1;
		break;
	case BTF_ID_KIND_SET8:
		prefixlen = sizeof(BTF_SET8 "__") - 1;
		break;
	default:
		pr_err("Unexpected kind %d passed to %s() for symbol %s\n", kind, __func__, name);
		return NULL;
	}

	id = name + prefixlen;
	if (id >= name + len) {
		pr_err("FAILED to parse set name: %s\n", name);
		return NULL;
	}

	return btf_id__add_unique(&obj->sets, id, kind);
}

static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
{
	char *id;

	id = get_id(name + size);
	if (!id) {
		pr_err("FAILED to parse symbol name: %s\n", name);
		return NULL;
	}

	return btf_id__add(root, id, BTF_ID_KIND_SYM);
}

static void bswap_32_data(void *data, u32 nr_bytes)
{
	u32 cnt, i;
	u32 *ptr;

	cnt = nr_bytes / sizeof(u32);
	ptr = data;

	for (i = 0; i < cnt; i++)
		ptr[i] = bswap_32(ptr[i]);
}

static int elf_collect(struct object *obj)
{
	Elf_Scn *scn = NULL;
	size_t shdrstrndx;
	GElf_Ehdr ehdr;
	int idx = 0;
	Elf *elf;
	int fd;

	fd = open(obj->path, O_RDWR, 0666);
	if (fd == -1) {
		pr_err("FAILED cannot open %s: %s\n",
			obj->path, strerror(errno));
		return -1;
	}

	elf_version(EV_CURRENT);

	elf = elf_begin(fd, ELF_C_READ_MMAP_PRIVATE, NULL);
	if (!elf) {
		close(fd);
		pr_err("FAILED cannot create ELF descriptor: %s\n",
			elf_errmsg(-1));
		return -1;
	}

	obj->efile.fd  = fd;
	obj->efile.elf = elf;

	elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT);

	if (elf_getshdrstrndx(elf, &shdrstrndx) != 0) {
		pr_err("FAILED cannot get shdr str ndx\n");
		return -1;
	}

	if (gelf_getehdr(obj->efile.elf, &ehdr) == NULL) {
		pr_err("FAILED cannot get ELF header: %s\n",
			elf_errmsg(-1));
		return -1;
	}
	obj->efile.encoding = ehdr.e_ident[EI_DATA];

	/*
	 * Scan all the elf sections and look for save data
	 * from .BTF_ids section and symbols.
	 */
	while ((scn = elf_nextscn(elf, scn)) != NULL) {
		Elf_Data *data;
		GElf_Shdr sh;
		char *name;

		idx++;
		if (gelf_getshdr(scn, &sh) != &sh) {
			pr_err("FAILED get section(%d) header\n", idx);
			return -1;
		}

		name = elf_strptr(elf, shdrstrndx, sh.sh_name);
		if (!name) {
			pr_err("FAILED get section(%d) name\n", idx);
			return -1;
		}

		data = elf_getdata(scn, 0);
		if (!data) {
			pr_err("FAILED to get section(%d) data from %s\n",
				idx, name);
			return -1;
		}

		pr_debug2("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
			  idx, name, (unsigned long) data->d_size,
			  (int) sh.sh_link, (unsigned long) sh.sh_flags,
			  (int) sh.sh_type);

		if (sh.sh_type == SHT_SYMTAB) {
			obj->efile.symbols       = data;
			obj->efile.symbols_shndx = idx;
			obj->efile.strtabidx     = sh.sh_link;
		} else if (!strcmp(name, BTF_IDS_SECTION)) {
			/*
			 * If target endianness differs from host, we need to bswap32
			 * the .BTF_ids section data on load, because .BTF_ids has
			 * Elf_Type = ELF_T_BYTE, and so libelf returns data buffer in
			 * the target endianness. We repeat this on dump.
			 */
			if (obj->efile.encoding != ELFDATANATIVE) {
				pr_debug("bswap_32 .BTF_ids data from target to host endianness\n");
				bswap_32_data(data->d_buf, data->d_size);
			}
			obj->efile.idlist       = data;
			obj->efile.idlist_shndx = idx;
			obj->efile.idlist_addr  = sh.sh_addr;
		}
	}

	return 0;
}

static int symbols_collect(struct object *obj)
{
	Elf_Scn *scn = NULL;
	int n, i;
	GElf_Shdr sh;
	char *name;

	scn = elf_getscn(obj->efile.elf, obj->efile.symbols_shndx);
	if (!scn)
		return -1;

	if (gelf_getshdr(scn, &sh) != &sh)
		return -1;

	n = sh.sh_size / sh.sh_entsize;

	/*
	 * Scan symbols and look for the ones starting with
	 * __BTF_ID__* over .BTF_ids section.
	 */
	for (i = 0; i < n; i++) {
		char *prefix;
		struct btf_id *id;
		GElf_Sym sym;

		if (!gelf_getsym(obj->efile.symbols, i, &sym))
			return -1;

		if (sym.st_shndx != obj->efile.idlist_shndx)
			continue;

		name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
				  sym.st_name);

		if (!is_btf_id(name))
			continue;

		/*
		 * __BTF_ID__TYPE__vfs_truncate__0
		 * prefix =  ^
		 */
		prefix = name + sizeof(BTF_ID_PREFIX) - 1;

		/* struct */
		if (!strncmp(prefix, BTF_STRUCT, sizeof(BTF_STRUCT) - 1)) {
			obj->nr_structs++;
			id = add_symbol(&obj->structs, prefix, sizeof(BTF_STRUCT) - 1);
		/* union  */
		} else if (!strncmp(prefix, BTF_UNION, sizeof(BTF_UNION) - 1)) {
			obj->nr_unions++;
			id = add_symbol(&obj->unions, prefix, sizeof(BTF_UNION) - 1);
		/* typedef */
		} else if (!strncmp(prefix, BTF_TYPEDEF, sizeof(BTF_TYPEDEF) - 1)) {
			obj->nr_typedefs++;
			id = add_symbol(&obj->typedefs, prefix, sizeof(BTF_TYPEDEF) - 1);
		/* func */
		} else if (!strncmp(prefix, BTF_FUNC, sizeof(BTF_FUNC) - 1)) {
			obj->nr_funcs++;
			id = add_symbol(&obj->funcs, prefix, sizeof(BTF_FUNC) - 1);
		/* set8 */
		} else if (!strncmp(prefix, BTF_SET8, sizeof(BTF_SET8) - 1)) {
			id = add_set(obj, prefix, BTF_ID_KIND_SET8);
			/*
			 * SET8 objects store list's count, which is encoded
			 * in symbol's size, together with 'cnt' field hence
			 * that - 1.
			 */
			if (id)
				id->cnt = sym.st_size / sizeof(uint64_t) - 1;
		/* set */
		} else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
			id = add_set(obj, prefix, BTF_ID_KIND_SET);
			/*
			 * SET objects store list's count, which is encoded
			 * in symbol's size, together with 'cnt' field hence
			 * that - 1.
			 */
			if (id)
				id->cnt = sym.st_size / sizeof(int) - 1;
		} else {
			pr_err("FAILED unsupported prefix %s\n", prefix);
			return -1;
		}

		if (!id)
			return -EINVAL;

		if (id->addr_cnt >= ADDR_CNT) {
			pr_err("FAILED symbol %s crossed the number of allowed lists\n",
				id->name);
			return -1;
		}
		id->addr[id->addr_cnt++] = sym.st_value;
	}

	return 0;
}

static int load_btf(struct object *obj)
{
	struct btf *base_btf = NULL, *btf = NULL;
	int err;

	if (obj->base_btf_path) {
		base_btf = btf__parse(obj->base_btf_path, NULL);
		err = libbpf_get_error(base_btf);
		if (err) {
			pr_err("FAILED: load base BTF from %s: %s\n",
			       obj->base_btf_path, strerror(-err));
			goto out_err;
		}
	}

	btf = btf__parse_split(obj->btf_path ?: obj->path, base_btf);
	err = libbpf_get_error(btf);
	if (err) {
		pr_err("FAILED: load BTF from %s: %s\n",
			obj->btf_path ?: obj->path, strerror(-err));
		goto out_err;
	}

	obj->base_btf = base_btf;
	obj->btf = btf;

	return 0;

out_err:
	btf__free(base_btf);
	btf__free(btf);
	obj->base_btf = NULL;
	obj->btf = NULL;
	return err;
}

static int symbols_resolve(struct object *obj)
{
	int nr_typedefs = obj->nr_typedefs;
	int nr_structs  = obj->nr_structs;
	int nr_unions   = obj->nr_unions;
	int nr_funcs    = obj->nr_funcs;
	struct btf *btf = obj->btf;
	int err, type_id;
	__u32 nr_types;

	err = -1;
	nr_types = btf__type_cnt(btf);

	/*
	 * Iterate all the BTF types and search for collected symbol IDs.
	 */
	for (type_id = 1; type_id < nr_types; type_id++) {
		const struct btf_type *type;
		struct rb_root *root;
		struct btf_id *id;
		const char *str;
		int *nr;

		type = btf__type_by_id(btf, type_id);
		if (!type) {
			pr_err("FAILED: malformed BTF, can't resolve type for ID %d\n",
				type_id);
			goto out;
		}

		if (btf_is_func(type) && nr_funcs) {
			nr   = &nr_funcs;
			root = &obj->funcs;
		} else if (btf_is_struct(type) && nr_structs) {
			nr   = &nr_structs;
			root = &obj->structs;
		} else if (btf_is_union(type) && nr_unions) {
			nr   = &nr_unions;
			root = &obj->unions;
		} else if (btf_is_typedef(type) && nr_typedefs) {
			nr   = &nr_typedefs;
			root = &obj->typedefs;
		} else
			continue;

		str = btf__name_by_offset(btf, type->name_off);
		if (!str) {
			pr_err("FAILED: malformed BTF, can't resolve name for ID %d\n",
				type_id);
			goto out;
		}

		id = btf_id__find(root, str);
		if (id) {
			if (id->id) {
				pr_info("WARN: multiple IDs found for '%s': %d, %d - using %d\n",
					str, id->id, type_id, id->id);
				warnings++;
			} else {
				id->id = type_id;
				(*nr)--;
			}
		}
	}

	err = 0;
out:
	return err;
}

static int id_patch(struct object *obj, struct btf_id *id)
{
	Elf_Data *data = obj->efile.idlist;
	int *ptr = data->d_buf;
	int i;

	/* For set, set8, id->id may be 0 */
	if (!id->id && id->kind != BTF_ID_KIND_SET && id->kind != BTF_ID_KIND_SET8) {
		pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name);
		warnings++;
	}

	for (i = 0; i < id->addr_cnt; i++) {
		unsigned long addr = id->addr[i];
		unsigned long idx = addr - obj->efile.idlist_addr;

		pr_debug("patching addr %5lu: ID %7d [%s]\n",
			 idx, id->id, id->name);

		if (idx >= data->d_size) {
			pr_err("FAILED patching index %lu out of bounds %lu\n",
				idx, data->d_size);
			return -1;
		}

		idx = idx / sizeof(int);
		ptr[idx] = id->id;
	}

	return 0;
}

static int __symbols_patch(struct object *obj, struct rb_root *root)
{
	struct rb_node *next;
	struct btf_id *id;

	next = rb_first(root);
	while (next) {
		id = rb_entry(next, struct btf_id, rb_node);

		if (id_patch(obj, id))
			return -1;

		next = rb_next(next);
	}
	return 0;
}

static int cmp_id(const void *pa, const void *pb)
{
	const int *a = pa, *b = pb;

	return *a - *b;
}

static int sets_patch(struct object *obj)
{
	Elf_Data *data = obj->efile.idlist;
	struct rb_node *next;
	int cnt;

	next = rb_first(&obj->sets);
	while (next) {
		struct btf_id_set8 *set8 = NULL;
		struct btf_id_set *set = NULL;
		unsigned long addr, off;
		struct btf_id *id;

		id   = rb_entry(next, struct btf_id, rb_node);
		addr = id->addr[0];
		off = addr - obj->efile.idlist_addr;

		/* sets are unique */
		if (id->addr_cnt != 1) {
			pr_err("FAILED malformed data for set '%s'\n",
				id->name);
			return -1;
		}

		switch (id->kind) {
		case BTF_ID_KIND_SET:
			set = data->d_buf + off;
			cnt = set->cnt;
			qsort(set->ids, set->cnt, sizeof(set->ids[0]), cmp_id);
			break;
		case BTF_ID_KIND_SET8:
			set8 = data->d_buf + off;
			cnt = set8->cnt;
			/*
			 * Make sure id is at the beginning of the pairs
			 * struct, otherwise the below qsort would not work.
			 */
			BUILD_BUG_ON((u32 *)set8->pairs != &set8->pairs[0].id);
			qsort(set8->pairs, set8->cnt, sizeof(set8->pairs[0]), cmp_id);
			break;
		default:
			pr_err("Unexpected btf_id_kind %d for set '%s'\n", id->kind, id->name);
			return -1;
		}

		pr_debug("sorting  addr %5lu: cnt %6d [%s]\n", off, cnt, id->name);

		next = rb_next(next);
	}
	return 0;
}

static int symbols_patch(struct object *obj)
{
	if (__symbols_patch(obj, &obj->structs)  ||
	    __symbols_patch(obj, &obj->unions)   ||
	    __symbols_patch(obj, &obj->typedefs) ||
	    __symbols_patch(obj, &obj->funcs)    ||
	    __symbols_patch(obj, &obj->sets))
		return -1;

	if (sets_patch(obj))
		return -1;

	return 0;
}

static int dump_raw_data(const char *out_path, const void *data, u32 size)
{
	size_t written;
	FILE *file;

	file = fopen(out_path, "wb");
	if (!file) {
		pr_err("Couldn't open %s for writing\n", out_path);
		return -1;
	}

	written = fwrite(data, 1, size, file);
	if (written != size) {
		pr_err("Failed to write data to %s\n", out_path);
		fclose(file);
		unlink(out_path);
		return -1;
	}

	fclose(file);
	pr_debug("Dumped %lu bytes of data to %s\n", size, out_path);

	return 0;
}

static int dump_raw_btf_ids(struct object *obj, const char *out_path)
{
	Elf_Data *data = obj->efile.idlist;
	int err;

	if (!data || !data->d_buf) {
		pr_debug("%s has no BTF_ids data to dump\n", obj->path);
		return 0;
	}

	/*
	 * If target endianness differs from host, we need to bswap32 the
	 * .BTF_ids section data before dumping so that the output is in
	 * target endianness.
	 */
	if (obj->efile.encoding != ELFDATANATIVE) {
		pr_debug("bswap_32 .BTF_ids data from host to target endianness\n");
		bswap_32_data(data->d_buf, data->d_size);
	}

	err = dump_raw_data(out_path, data->d_buf, data->d_size);
	if (err)
		return -1;

	return 0;
}

static int dump_raw_btf(struct btf *btf, const char *out_path)
{
	const void *raw_btf_data;
	u32 raw_btf_size;
	int err;

	raw_btf_data = btf__raw_data(btf, &raw_btf_size);
	if (!raw_btf_data) {
		pr_err("btf__raw_data() failed\n");
		return -1;
	}

	err = dump_raw_data(out_path, raw_btf_data, raw_btf_size);
	if (err)
		return -1;

	return 0;
}

static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf, s32 type_id)
{
	const struct btf_type *t = btf__type_by_id(btf, type_id);

	while (btf_is_mod(t))
		t = btf__type_by_id(btf, t->type);

	return t;
}

static int push_decl_tag_id(struct btf2btf_context *ctx, u32 decl_tag_id)
{
	u32 *arr = ctx->decl_tags;
	u32 cap = ctx->max_decl_tags;

	if (ctx->nr_decl_tags + 1 > cap) {
		cap = max(cap + 256, cap * 2);
		arr = realloc(arr, sizeof(u32) * cap);
		if (!arr)
			return -ENOMEM;
		ctx->max_decl_tags = cap;
		ctx->decl_tags = arr;
	}

	ctx->decl_tags[ctx->nr_decl_tags++] = decl_tag_id;

	return 0;
}

static int push_kfunc(struct btf2btf_context *ctx, struct kfunc *kfunc)
{
	struct kfunc *arr = ctx->kfuncs;
	u32 cap = ctx->max_kfuncs;

	if (ctx->nr_kfuncs + 1 > cap) {
		cap = max(cap + 256, cap * 2);
		arr = realloc(arr, sizeof(struct kfunc) * cap);
		if (!arr)
			return -ENOMEM;
		ctx->max_kfuncs = cap;
		ctx->kfuncs = arr;
	}

	ctx->kfuncs[ctx->nr_kfuncs++] = *kfunc;

	return 0;
}

static int collect_decl_tags(struct btf2btf_context *ctx)
{
	const u32 type_cnt = btf__type_cnt(ctx->btf);
	struct btf *btf = ctx->btf;
	const struct btf_type *t;
	int err;

	for (u32 id = 1; id < type_cnt; id++) {
		t = btf__type_by_id(btf, id);
		if (!btf_is_decl_tag(t))
			continue;
		err = push_decl_tag_id(ctx, id);
		if (err)
			return err;
	}

	return 0;
}

/*
 * To find the kfunc flags having its struct btf_id (with ELF addresses)
 * we need to find the address that is in range of a set8.
 * If a set8 is found, then the flags are located at addr + 4 bytes.
 * Return 0 (no flags!) if not found.
 */
static u32 find_kfunc_flags(struct object *obj, struct btf_id *kfunc_id)
{
	const u32 *elf_data_ptr = obj->efile.idlist->d_buf;
	u64 set_lower_addr, set_upper_addr, addr;
	struct btf_id *set_id;
	struct rb_node *next;
	u32 flags;
	u64 idx;

	for (next = rb_first(&obj->sets); next; next = rb_next(next)) {
		set_id = rb_entry(next, struct btf_id, rb_node);
		if (set_id->kind != BTF_ID_KIND_SET8 || set_id->addr_cnt != 1)
			continue;

		set_lower_addr = set_id->addr[0];
		set_upper_addr = set_lower_addr + set_id->cnt * sizeof(u64);

		for (u32 i = 0; i < kfunc_id->addr_cnt; i++) {
			addr = kfunc_id->addr[i];
			/*
			 * Lower bound is exclusive to skip the 8-byte header of the set.
			 * Upper bound is inclusive to capture the last entry at offset 8*cnt.
			 */
			if (set_lower_addr < addr && addr <= set_upper_addr) {
				pr_debug("found kfunc %s in BTF_ID_FLAGS %s\n",
					 kfunc_id->name, set_id->name);
				idx = addr - obj->efile.idlist_addr;
				idx = idx / sizeof(u32) + 1;
				flags = elf_data_ptr[idx];

				return flags;
			}
		}
	}

	return 0;
}

static int collect_kfuncs(struct object *obj, struct btf2btf_context *ctx)
{
	const char *tag_name, *func_name;
	struct btf *btf = ctx->btf;
	const struct btf_type *t;
	u32 flags, func_id;
	struct kfunc kfunc;
	struct btf_id *id;
	int err;

	if (ctx->nr_decl_tags == 0)
		return 0;

	for (u32 i = 0; i < ctx->nr_decl_tags; i++) {
		t = btf__type_by_id(btf, ctx->decl_tags[i]);
		if (btf_kflag(t) || btf_decl_tag(t)->component_idx != -1)
			continue;

		tag_name = btf__name_by_offset(btf, t->name_off);
		if (strcmp(tag_name, "bpf_kfunc") != 0)
			continue;

		func_id = t->type;
		t = btf__type_by_id(btf, func_id);
		if (!btf_is_func(t))
			continue;

		func_name = btf__name_by_offset(btf, t->name_off);
		if (!func_name)
			continue;

		id = btf_id__find(&obj->funcs, func_name);
		if (!id || id->kind != BTF_ID_KIND_SYM)
			continue;

		flags = find_kfunc_flags(obj, id);

		kfunc.name = id->name;
		kfunc.btf_id = func_id;
		kfunc.flags = flags;

		err = push_kfunc(ctx, &kfunc);
		if (err)
			return err;
	}

	return 0;
}

static int build_btf2btf_context(struct object *obj, struct btf2btf_context *ctx)
{
	int err;

	ctx->btf = obj->btf;

	err = collect_decl_tags(ctx);
	if (err) {
		pr_err("ERROR: resolve_btfids: failed to collect decl tags from BTF\n");
		return err;
	}

	err = collect_kfuncs(obj, ctx);
	if (err) {
		pr_err("ERROR: resolve_btfids: failed to collect kfuncs from BTF\n");
		return err;
	}

	return 0;
}


/* Implicit BPF kfunc arguments can only be of particular types */
static bool is_kf_implicit_arg(const struct btf *btf, const struct btf_param *p)
{
	static const char *const kf_implicit_arg_types[] = {
		"bpf_prog_aux",
	};
	const struct btf_type *t;
	const char *name;

	t = btf_type_skip_qualifiers(btf, p->type);
	if (!btf_is_ptr(t))
		return false;

	t = btf_type_skip_qualifiers(btf, t->type);
	if (!btf_is_struct(t))
		return false;

	name = btf__name_by_offset(btf, t->name_off);
	if (!name)
		return false;

	for (int i = 0; i < ARRAY_SIZE(kf_implicit_arg_types); i++)
		if (strcmp(name, kf_implicit_arg_types[i]) == 0)
			return true;

	return false;
}

/*
 * For a kfunc with KF_IMPLICIT_ARGS we do the following:
 *   1. Add a new function with _impl suffix in the name, with the prototype
 *      of the original kfunc.
 *   2. Add all decl tags except "bpf_kfunc" for the _impl func.
 *   3. Add a new function prototype with modified list of arguments:
 *      omitting implicit args.
 *   4. Change the prototype of the original kfunc to the new one.
 *
 * This way we transform the BTF associated with the kfunc from
 *	__bpf_kfunc bpf_foo(int arg1, void *implicit_arg);
 * into
 *	bpf_foo_impl(int arg1, void *implicit_arg);
 *	__bpf_kfunc bpf_foo(int arg1);
 *
 * If a kfunc with KF_IMPLICIT_ARGS already has an _impl counterpart
 * in BTF, then it's a legacy case: an _impl function is declared in the
 * source code. In this case, we can skip adding an _impl function, but we
 * still have to add a func prototype that omits implicit args.
 */
static int process_kfunc_with_implicit_args(struct btf2btf_context *ctx, struct kfunc *kfunc)
{
	s32 idx, new_proto_id, new_func_id, proto_id;
	const char *param_name, *tag_name;
	const struct btf_param *params;
	enum btf_func_linkage linkage;
	char tmp_name[KSYM_NAME_LEN];
	struct btf *btf = ctx->btf;
	int err, len, nr_params;
	struct btf_type *t;

	t = (struct btf_type *)btf__type_by_id(btf, kfunc->btf_id);
	if (!t || !btf_is_func(t)) {
		pr_err("ERROR: resolve_btfids: btf id %d is not a function\n", kfunc->btf_id);
		return -EINVAL;
	}

	linkage = btf_vlen(t);

	proto_id = t->type;
	t = (struct btf_type *)btf__type_by_id(btf, proto_id);
	if (!t || !btf_is_func_proto(t)) {
		pr_err("ERROR: resolve_btfids: btf id %d is not a function prototype\n", proto_id);
		return -EINVAL;
	}

	len = snprintf(tmp_name, sizeof(tmp_name), "%s%s", kfunc->name, KF_IMPL_SUFFIX);
	if (len < 0 || len >= sizeof(tmp_name)) {
		pr_err("ERROR: function name is too long: %s%s\n", kfunc->name, KF_IMPL_SUFFIX);
		return -E2BIG;
	}

	if (btf__find_by_name_kind(btf, tmp_name, BTF_KIND_FUNC) > 0) {
		pr_debug("resolve_btfids: function %s already exists in BTF\n", tmp_name);
		goto add_new_proto;
	}

	/* Add a new function with _impl suffix and original prototype */
	new_func_id = btf__add_func(btf, tmp_name, linkage, proto_id);
	if (new_func_id < 0) {
		pr_err("ERROR: resolve_btfids: failed to add func %s to BTF\n", tmp_name);
		return new_func_id;
	}

	/* Copy all decl tags except "bpf_kfunc" from the original kfunc to the new one */
	for (int i = 0; i < ctx->nr_decl_tags; i++) {
		t = (struct btf_type *)btf__type_by_id(btf, ctx->decl_tags[i]);
		if (t->type != kfunc->btf_id)
			continue;

		tag_name = btf__name_by_offset(btf, t->name_off);
		if (strcmp(tag_name, "bpf_kfunc") == 0)
			continue;

		idx = btf_decl_tag(t)->component_idx;

		if (btf_kflag(t))
			err = btf__add_decl_attr(btf, tag_name, new_func_id, idx);
		else
			err = btf__add_decl_tag(btf, tag_name, new_func_id, idx);

		if (err < 0) {
			pr_err("ERROR: resolve_btfids: failed to add decl tag %s for %s\n",
			       tag_name, tmp_name);
			return -EINVAL;
		}
	}

add_new_proto:
	t = (struct btf_type *)btf__type_by_id(btf, proto_id);
	new_proto_id = btf__add_func_proto(btf, t->type);
	if (new_proto_id < 0) {
		pr_err("ERROR: resolve_btfids: failed to add func proto for %s\n", kfunc->name);
		return new_proto_id;
	}

	/* Add non-implicit args to the new prototype */
	t = (struct btf_type *)btf__type_by_id(btf, proto_id);
	nr_params = btf_vlen(t);
	for (int i = 0; i < nr_params; i++) {
		params = btf_params(t);
		if (is_kf_implicit_arg(btf, &params[i]))
			break;
		param_name = btf__name_by_offset(btf, params[i].name_off);
		err = btf__add_func_param(btf, param_name, params[i].type);
		if (err < 0) {
			pr_err("ERROR: resolve_btfids: failed to add param %s for %s\n",
			       param_name, kfunc->name);
			return err;
		}
		t = (struct btf_type *)btf__type_by_id(btf, proto_id);
	}

	/* Finally change the prototype of the original kfunc to the new one */
	t = (struct btf_type *)btf__type_by_id(btf, kfunc->btf_id);
	t->type = new_proto_id;

	pr_debug("resolve_btfids: updated BTF for kfunc with implicit args %s\n", kfunc->name);

	return 0;
}

static int btf2btf(struct object *obj)
{
	struct btf2btf_context ctx = {};
	int err;

	err = build_btf2btf_context(obj, &ctx);
	if (err)
		goto out;

	for (u32 i = 0; i < ctx.nr_kfuncs; i++) {
		struct kfunc *kfunc = &ctx.kfuncs[i];

		if (!(kfunc->flags & KF_IMPLICIT_ARGS))
			continue;

		err = process_kfunc_with_implicit_args(&ctx, kfunc);
		if (err)
			goto out;
	}

	err = 0;
out:
	free(ctx.decl_tags);
	free(ctx.kfuncs);

	return err;
}

/*
 * Sort types by name in ascending order resulting in all
 * anonymous types being placed before named types.
 */
static int cmp_type_names(const void *a, const void *b, void *priv)
{
	struct btf *btf = (struct btf *)priv;
	const struct btf_type *ta = btf__type_by_id(btf, *(__u32 *)a);
	const struct btf_type *tb = btf__type_by_id(btf, *(__u32 *)b);
	const char *na, *nb;
	int r;

	na = btf__str_by_offset(btf, ta->name_off);
	nb = btf__str_by_offset(btf, tb->name_off);
	r = strcmp(na, nb);
	if (r != 0)
		return r;

	/* preserve original relative order of anonymous or same-named types */
	return *(__u32 *)a < *(__u32 *)b ? -1 : 1;
}

static int sort_btf_by_name(struct btf *btf)
{
	__u32 *permute_ids = NULL, *id_map = NULL;
	int nr_types, i, err = 0;
	__u32 start_id = 0, id;

	if (btf__base_btf(btf))
		start_id = btf__type_cnt(btf__base_btf(btf));
	nr_types = btf__type_cnt(btf) - start_id;

	permute_ids = calloc(nr_types, sizeof(*permute_ids));
	if (!permute_ids) {
		err = -ENOMEM;
		goto out;
	}

	id_map = calloc(nr_types, sizeof(*id_map));
	if (!id_map) {
		err = -ENOMEM;
		goto out;
	}

	for (i = 0, id = start_id; i < nr_types; i++, id++)
		permute_ids[i] = id;

	qsort_r(permute_ids, nr_types, sizeof(*permute_ids), cmp_type_names,
		btf);

	for (i = 0; i < nr_types; i++) {
		id = permute_ids[i] - start_id;
		id_map[id] = i + start_id;
	}

	err = btf__permute(btf, id_map, nr_types, NULL);
	if (err)
		pr_err("FAILED: btf permute: %s\n", strerror(-err));

out:
	free(permute_ids);
	free(id_map);
	return err;
}

static int finalize_btf(struct object *obj)
{
	struct btf *base_btf = obj->base_btf, *btf = obj->btf;
	int err;

	if (obj->base_btf && obj->distill_base) {
		err = btf__distill_base(obj->btf, &base_btf, &btf);
		if (err) {
			pr_err("FAILED to distill base BTF: %s\n", strerror(errno));
			goto out_err;
		}

		btf__free(obj->base_btf);
		btf__free(obj->btf);
		obj->base_btf = base_btf;
		obj->btf = btf;
	}

	err = sort_btf_by_name(obj->btf);
	if (err) {
		pr_err("FAILED to sort BTF: %s\n", strerror(errno));
		goto out_err;
	}

	return 0;

out_err:
	btf__free(base_btf);
	btf__free(btf);
	obj->base_btf = NULL;
	obj->btf = NULL;

	return err;
}

static inline int make_out_path(char *buf, u32 buf_sz, const char *in_path, const char *suffix)
{
	int len = snprintf(buf, buf_sz, "%s%s", in_path, suffix);

	if (len < 0 || len >= buf_sz) {
		pr_err("Output path is too long: %s%s\n", in_path, suffix);
		return -E2BIG;
	}

	return 0;
}

/*
 * Patch the .BTF_ids section of an ELF file with data from provided file.
 * Equivalent to: objcopy --update-section .BTF_ids=<btfids> <elf>
 *
 * 1. Find .BTF_ids section in the ELF
 * 2. Verify that blob file size matches section size
 * 3. Update section data buffer with blob data
 * 4. Write the ELF file
 */
static int patch_btfids(const char *btfids_path, const char *elf_path)
{
	Elf_Scn *scn = NULL;
	FILE *btfids_file;
	size_t shdrstrndx;
	int fd, err = -1;
	Elf_Data *data;
	struct stat st;
	GElf_Shdr sh;
	char *name;
	Elf *elf;

	elf_version(EV_CURRENT);

	fd = open(elf_path, O_RDWR, 0666);
	if (fd < 0) {
		pr_err("FAILED to open %s: %s\n", elf_path, strerror(errno));
		return -1;
	}

	elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
	if (!elf) {
		close(fd);
		pr_err("FAILED cannot create ELF descriptor: %s\n", elf_errmsg(-1));
		return -1;
	}

	elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT);

	if (elf_getshdrstrndx(elf, &shdrstrndx) != 0) {
		pr_err("FAILED cannot get shdr str ndx\n");
		goto out;
	}

	while ((scn = elf_nextscn(elf, scn)) != NULL) {

		if (gelf_getshdr(scn, &sh) != &sh) {
			pr_err("FAILED to get section header\n");
			goto out;
		}

		name = elf_strptr(elf, shdrstrndx, sh.sh_name);
		if (!name)
			continue;

		if (strcmp(name, BTF_IDS_SECTION) == 0)
			break;
	}

	if (!scn) {
		pr_err("FAILED: section %s not found in %s\n", BTF_IDS_SECTION, elf_path);
		goto out;
	}

	data = elf_getdata(scn, NULL);
	if (!data) {
		pr_err("FAILED to get %s section data from %s\n", BTF_IDS_SECTION, elf_path);
		goto out;
	}

	if (stat(btfids_path, &st) < 0) {
		pr_err("FAILED to stat %s: %s\n", btfids_path, strerror(errno));
		goto out;
	}

	if ((size_t)st.st_size != data->d_size) {
		pr_err("FAILED: size mismatch - %s section in %s is %zu bytes, %s is %zu bytes\n",
		       BTF_IDS_SECTION, elf_path, data->d_size, btfids_path, (size_t)st.st_size);
		goto out;
	}

	btfids_file = fopen(btfids_path, "rb");
	if (!btfids_file) {
		pr_err("FAILED to open %s: %s\n", btfids_path, strerror(errno));
		goto out;
	}

	pr_debug("Copying data from %s to %s section of %s (%zu bytes)\n",
		 btfids_path, BTF_IDS_SECTION, elf_path, data->d_size);

	if (fread(data->d_buf, data->d_size, 1, btfids_file) != 1) {
		pr_err("FAILED to read %s\n", btfids_path);
		fclose(btfids_file);
		goto out;
	}
	fclose(btfids_file);

	elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
	if (elf_update(elf, ELF_C_WRITE) < 0) {
		pr_err("FAILED to update ELF file %s\n", elf_path);
		goto out;
	}

	err = 0;
out:
	elf_end(elf);
	close(fd);

	return err;
}

static const char * const resolve_btfids_usage[] = {
	"resolve_btfids [<options>] <ELF object>",
	"resolve_btfids --patch_btfids <.BTF_ids file> <ELF object>",
	NULL
};

int main(int argc, const char **argv)
{
	struct object obj = {
		.efile = {
			.idlist_shndx  = -1,
			.symbols_shndx = -1,
		},
		.structs  = RB_ROOT,
		.unions   = RB_ROOT,
		.typedefs = RB_ROOT,
		.funcs    = RB_ROOT,
		.sets     = RB_ROOT,
	};
	const char *btfids_path = NULL;
	bool fatal_warnings = false;
	bool resolve_btfids = true;
	char out_path[PATH_MAX];

	struct option btfid_options[] = {
		OPT_INCR('v', "verbose", &verbose,
			 "be more verbose (show errors, etc)"),
		OPT_STRING(0, "btf", &obj.btf_path, "file",
			   "path to a file with input BTF data"),
		OPT_STRING('b', "btf_base", &obj.base_btf_path, "file",
			   "path of file providing base BTF"),
		OPT_BOOLEAN(0, "fatal_warnings", &fatal_warnings,
			    "turn warnings into errors"),
		OPT_BOOLEAN(0, "distill_base", &obj.distill_base,
			    "distill --btf_base and emit .BTF.base section data"),
		OPT_STRING(0, "patch_btfids", &btfids_path, "file",
			   "path to .BTF_ids section data blob to patch into ELF file"),
		OPT_END()
	};
	int err = -1;

	argc = parse_options(argc, argv, btfid_options, resolve_btfids_usage,
			     PARSE_OPT_STOP_AT_NON_OPTION);
	if (argc != 1)
		usage_with_options(resolve_btfids_usage, btfid_options);

	obj.path = argv[0];

	if (btfids_path)
		return patch_btfids(btfids_path, obj.path);

	if (elf_collect(&obj))
		goto out;

	/*
	 * We did not find .BTF_ids section or symbols section,
	 * nothing to do..
	 */
	if (obj.efile.idlist_shndx == -1 ||
	    obj.efile.symbols_shndx == -1) {
		pr_debug("Cannot find .BTF_ids or symbols sections, skip symbols resolution\n");
		resolve_btfids = false;
	}

	if (resolve_btfids)
		if (symbols_collect(&obj))
			goto out;

	if (load_btf(&obj))
		goto out;

	if (btf2btf(&obj))
		goto out;

	if (finalize_btf(&obj))
		goto out;

	if (!resolve_btfids)
		goto dump_btf;

	if (symbols_resolve(&obj))
		goto out;

	if (symbols_patch(&obj))
		goto out;

	err = make_out_path(out_path, sizeof(out_path), obj.path, BTF_IDS_SECTION);
	err = err ?: dump_raw_btf_ids(&obj, out_path);
	if (err)
		goto out;

dump_btf:
	err = make_out_path(out_path, sizeof(out_path), obj.path, BTF_ELF_SEC);
	err = err ?: dump_raw_btf(obj.btf, out_path);
	if (err)
		goto out;

	if (obj.base_btf && obj.distill_base) {
		err = make_out_path(out_path, sizeof(out_path), obj.path, BTF_BASE_ELF_SEC);
		err = err ?: dump_raw_btf(obj.base_btf, out_path);
		if (err)
			goto out;
	}

	if (!(fatal_warnings && warnings))
		err = 0;
out:
	btf__free(obj.base_btf);
	btf__free(obj.btf);
	if (obj.efile.elf) {
		elf_end(obj.efile.elf);
		close(obj.efile.fd);
	}
	return err;
}