// 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,
                                    const 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 = strdup(name);
                if (!id->name) {
                        free(id);
                        return NULL;
                }
                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,
                                         const 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,
                                                const char *name,
                                                enum btf_id_kind kind)
{
        return __btf_id__add(root, name, kind, true);
}

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

        if (pos >= len)
                return -1;

        if (len - pos >= buf_sz)
                return -1;

        strcpy(buf, prefix_end + pos);
        /*
         * __BTF_ID__func__vfs_truncate__0
         * buf =           ^
         *
         * cut the unique id part
         */
        p = strrchr(buf, '_');
        p--;
        if (*p != '_')
                return -1;
        *p = '\0';

        return 0;
}

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[KSYM_NAME_LEN];

        if (get_id(name + size, id, sizeof(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 btf_id__free_all(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);
                next = rb_next(&id->rb_node);
                rb_erase(&id->rb_node, root);
                free(id->name);
                free(id);
        }
}

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);
        btf_id__free_all(&obj.structs);
        btf_id__free_all(&obj.unions);
        btf_id__free_all(&obj.typedefs);
        btf_id__free_all(&obj.funcs);
        btf_id__free_all(&obj.sets);
        if (obj.efile.elf) {
                elf_end(obj.efile.elf);
                close(obj.efile.fd);
        }
        return err;
}