// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * elf.c - ELF access library
 *
 * Adapted from kpatch (https://github.com/dynup/kpatch):
 * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#include "elf.h"
#include "warn.h"

#define MAX_NAME_LEN 128

struct section *find_section_by_name(struct elf *elf, const char *name)
{
        struct section *sec;

        list_for_each_entry(sec, &elf->sections, list)
                if (!strcmp(sec->name, name))
                        return sec;

        return NULL;
}

static struct section *find_section_by_index(struct elf *elf,
                                             unsigned int idx)
{
        struct section *sec;

        list_for_each_entry(sec, &elf->sections, list)
                if (sec->idx == idx)
                        return sec;

        return NULL;
}

static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
{
        struct section *sec;
        struct symbol *sym;

        list_for_each_entry(sec, &elf->sections, list)
                hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
                        if (sym->idx == idx)
                                return sym;

        return NULL;
}

struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
{
        struct symbol *sym;

        list_for_each_entry(sym, &sec->symbol_list, list)
                if (sym->type != STT_SECTION &&
                    sym->offset == offset)
                        return sym;

        return NULL;
}

struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
{
        struct section *sec;
        struct symbol *sym;

        list_for_each_entry(sec, &elf->sections, list)
                list_for_each_entry(sym, &sec->symbol_list, list)
                        if (!strcmp(sym->name, name))
                                return sym;

        return NULL;
}

struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
{
        struct symbol *sym;

        list_for_each_entry(sym, &sec->symbol_list, list)
                if (sym->type != STT_SECTION &&
                    offset >= sym->offset && offset < sym->offset + sym->len)
                        return sym;

        return NULL;
}

struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
                                     unsigned int len)
{
        struct rela *rela;
        unsigned long o;

        if (!sec->rela)
                return NULL;

        for (o = offset; o < offset + len; o++)
                hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
                        if (rela->offset == o)
                                return rela;

        return NULL;
}

struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
{
        return find_rela_by_dest_range(sec, offset, 1);
}

struct symbol *find_containing_func(struct section *sec, unsigned long offset)
{
        struct symbol *func;

        list_for_each_entry(func, &sec->symbol_list, list)
                if (func->type == STT_FUNC && offset >= func->offset &&
                    offset < func->offset + func->len)
                        return func;

        return NULL;
}

static int read_sections(struct elf *elf)
{
        Elf_Scn *s = NULL;
        struct section *sec;
        size_t shstrndx, sections_nr;
        int i;

        if (elf_getshdrnum(elf->elf, &sections_nr)) {
                WARN_ELF("elf_getshdrnum");
                return -1;
        }

        if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
                WARN_ELF("elf_getshdrstrndx");
                return -1;
        }

        for (i = 0; i < sections_nr; i++) {
                sec = malloc(sizeof(*sec));
                if (!sec) {
                        perror("malloc");
                        return -1;
                }
                memset(sec, 0, sizeof(*sec));

                INIT_LIST_HEAD(&sec->symbol_list);
                INIT_LIST_HEAD(&sec->rela_list);
                hash_init(sec->rela_hash);
                hash_init(sec->symbol_hash);

                list_add_tail(&sec->list, &elf->sections);

                s = elf_getscn(elf->elf, i);
                if (!s) {
                        WARN_ELF("elf_getscn");
                        return -1;
                }

                sec->idx = elf_ndxscn(s);

                if (!gelf_getshdr(s, &sec->sh)) {
                        WARN_ELF("gelf_getshdr");
                        return -1;
                }

                sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
                if (!sec->name) {
                        WARN_ELF("elf_strptr");
                        return -1;
                }

                if (sec->sh.sh_size != 0) {
                        sec->data = elf_getdata(s, NULL);
                        if (!sec->data) {
                                WARN_ELF("elf_getdata");
                                return -1;
                        }
                        if (sec->data->d_off != 0 ||
                            sec->data->d_size != sec->sh.sh_size) {
                                WARN("unexpected data attributes for %s",
                                     sec->name);
                                return -1;
                        }
                }
                sec->len = sec->sh.sh_size;
        }

        /* sanity check, one more call to elf_nextscn() should return NULL */
        if (elf_nextscn(elf->elf, s)) {
                WARN("section entry mismatch");
                return -1;
        }

        return 0;
}

static int read_symbols(struct elf *elf)
{
        struct section *symtab, *sec;
        struct symbol *sym, *pfunc, *alias;
        struct list_head *entry, *tmp;
        int symbols_nr, i;
        char *coldstr;

        symtab = find_section_by_name(elf, ".symtab");
        if (!symtab) {
                WARN("missing symbol table");
                return -1;
        }

        symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;

        for (i = 0; i < symbols_nr; i++) {
                sym = malloc(sizeof(*sym));
                if (!sym) {
                        perror("malloc");
                        return -1;
                }
                memset(sym, 0, sizeof(*sym));
                alias = sym;

                sym->idx = i;

                if (!gelf_getsym(symtab->data, i, &sym->sym)) {
                        WARN_ELF("gelf_getsym");
                        goto err;
                }

                sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
                                       sym->sym.st_name);
                if (!sym->name) {
                        WARN_ELF("elf_strptr");
                        goto err;
                }

                sym->type = GELF_ST_TYPE(sym->sym.st_info);
                sym->bind = GELF_ST_BIND(sym->sym.st_info);

                if (sym->sym.st_shndx > SHN_UNDEF &&
                    sym->sym.st_shndx < SHN_LORESERVE) {
                        sym->sec = find_section_by_index(elf,
                                                         sym->sym.st_shndx);
                        if (!sym->sec) {
                                WARN("couldn't find section for symbol %s",
                                     sym->name);
                                goto err;
                        }
                        if (sym->type == STT_SECTION) {
                                sym->name = sym->sec->name;
                                sym->sec->sym = sym;
                        }
                } else
                        sym->sec = find_section_by_index(elf, 0);

                sym->offset = sym->sym.st_value;
                sym->len = sym->sym.st_size;

                /* sorted insert into a per-section list */
                entry = &sym->sec->symbol_list;
                list_for_each_prev(tmp, &sym->sec->symbol_list) {
                        struct symbol *s;

                        s = list_entry(tmp, struct symbol, list);

                        if (sym->offset > s->offset) {
                                entry = tmp;
                                break;
                        }

                        if (sym->offset == s->offset) {
                                if (sym->len && sym->len == s->len && alias == sym)
                                        alias = s;

                                if (sym->len >= s->len) {
                                        entry = tmp;
                                        break;
                                }
                        }
                }
                sym->alias = alias;
                list_add(&sym->list, entry);
                hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
        }

        /* Create parent/child links for any cold subfunctions */
        list_for_each_entry(sec, &elf->sections, list) {
                list_for_each_entry(sym, &sec->symbol_list, list) {
                        char pname[MAX_NAME_LEN + 1];
                        size_t pnamelen;
                        if (sym->type != STT_FUNC)
                                continue;
                        sym->pfunc = sym->cfunc = sym;
                        coldstr = strstr(sym->name, ".cold");
                        if (!coldstr)
                                continue;

                        pnamelen = coldstr - sym->name;
                        if (pnamelen > MAX_NAME_LEN) {
                                WARN("%s(): parent function name exceeds maximum length of %d characters",
                                     sym->name, MAX_NAME_LEN);
                                return -1;
                        }

                        strncpy(pname, sym->name, pnamelen);
                        pname[pnamelen] = '\0';
                        pfunc = find_symbol_by_name(elf, pname);

                        if (!pfunc) {
                                WARN("%s(): can't find parent function",
                                     sym->name);
                                return -1;
                        }

                        sym->pfunc = pfunc;
                        pfunc->cfunc = sym;

                        /*
                         * Unfortunately, -fnoreorder-functions puts the child
                         * inside the parent.  Remove the overlap so we can
                         * have sane assumptions.
                         *
                         * Note that pfunc->len now no longer matches
                         * pfunc->sym.st_size.
                         */
                        if (sym->sec == pfunc->sec &&
                            sym->offset >= pfunc->offset &&
                            sym->offset + sym->len == pfunc->offset + pfunc->len) {
                                pfunc->len -= sym->len;
                        }
                }
        }

        return 0;

err:
        free(sym);
        return -1;
}

static int read_relas(struct elf *elf)
{
        struct section *sec;
        struct rela *rela;
        int i;
        unsigned int symndx;

        list_for_each_entry(sec, &elf->sections, list) {
                if (sec->sh.sh_type != SHT_RELA)
                        continue;

                sec->base = find_section_by_name(elf, sec->name + 5);
                if (!sec->base) {
                        WARN("can't find base section for rela section %s",
                             sec->name);
                        return -1;
                }

                sec->base->rela = sec;

                for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
                        rela = malloc(sizeof(*rela));
                        if (!rela) {
                                perror("malloc");
                                return -1;
                        }
                        memset(rela, 0, sizeof(*rela));

                        if (!gelf_getrela(sec->data, i, &rela->rela)) {
                                WARN_ELF("gelf_getrela");
                                return -1;
                        }

                        rela->type = GELF_R_TYPE(rela->rela.r_info);
                        rela->addend = rela->rela.r_addend;
                        rela->offset = rela->rela.r_offset;
                        symndx = GELF_R_SYM(rela->rela.r_info);
                        rela->sym = find_symbol_by_index(elf, symndx);
                        rela->sec = sec;
                        if (!rela->sym) {
                                WARN("can't find rela entry symbol %d for %s",
                                     symndx, sec->name);
                                return -1;
                        }

                        list_add_tail(&rela->list, &sec->rela_list);
                        hash_add(sec->rela_hash, &rela->hash, rela->offset);

                }
        }

        return 0;
}

struct elf *elf_read(const char *name, int flags)
{
        struct elf *elf;
        Elf_Cmd cmd;

        elf_version(EV_CURRENT);

        elf = malloc(sizeof(*elf));
        if (!elf) {
                perror("malloc");
                return NULL;
        }
        memset(elf, 0, sizeof(*elf));

        INIT_LIST_HEAD(&elf->sections);

        elf->fd = open(name, flags);
        if (elf->fd == -1) {
                fprintf(stderr, "objtool: Can't open '%s': %s\n",
                        name, strerror(errno));
                goto err;
        }

        if ((flags & O_ACCMODE) == O_RDONLY)
                cmd = ELF_C_READ_MMAP;
        else if ((flags & O_ACCMODE) == O_RDWR)
                cmd = ELF_C_RDWR;
        else /* O_WRONLY */
                cmd = ELF_C_WRITE;

        elf->elf = elf_begin(elf->fd, cmd, NULL);
        if (!elf->elf) {
                WARN_ELF("elf_begin");
                goto err;
        }

        if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
                WARN_ELF("gelf_getehdr");
                goto err;
        }

        if (read_sections(elf))
                goto err;

        if (read_symbols(elf))
                goto err;

        if (read_relas(elf))
                goto err;

        return elf;

err:
        elf_close(elf);
        return NULL;
}

struct section *elf_create_section(struct elf *elf, const char *name,
                                   size_t entsize, int nr)
{
        struct section *sec, *shstrtab;
        size_t size = entsize * nr;
        Elf_Scn *s;
        Elf_Data *data;

        sec = malloc(sizeof(*sec));
        if (!sec) {
                perror("malloc");
                return NULL;
        }
        memset(sec, 0, sizeof(*sec));

        INIT_LIST_HEAD(&sec->symbol_list);
        INIT_LIST_HEAD(&sec->rela_list);
        hash_init(sec->rela_hash);
        hash_init(sec->symbol_hash);

        list_add_tail(&sec->list, &elf->sections);

        s = elf_newscn(elf->elf);
        if (!s) {
                WARN_ELF("elf_newscn");
                return NULL;
        }

        sec->name = strdup(name);
        if (!sec->name) {
                perror("strdup");
                return NULL;
        }

        sec->idx = elf_ndxscn(s);
        sec->len = size;
        sec->changed = true;

        sec->data = elf_newdata(s);
        if (!sec->data) {
                WARN_ELF("elf_newdata");
                return NULL;
        }

        sec->data->d_size = size;
        sec->data->d_align = 1;

        if (size) {
                sec->data->d_buf = malloc(size);
                if (!sec->data->d_buf) {
                        perror("malloc");
                        return NULL;
                }
                memset(sec->data->d_buf, 0, size);
        }

        if (!gelf_getshdr(s, &sec->sh)) {
                WARN_ELF("gelf_getshdr");
                return NULL;
        }

        sec->sh.sh_size = size;
        sec->sh.sh_entsize = entsize;
        sec->sh.sh_type = SHT_PROGBITS;
        sec->sh.sh_addralign = 1;
        sec->sh.sh_flags = SHF_ALLOC;


        /* Add section name to .shstrtab (or .strtab for Clang) */
        shstrtab = find_section_by_name(elf, ".shstrtab");
        if (!shstrtab)
                shstrtab = find_section_by_name(elf, ".strtab");
        if (!shstrtab) {
                WARN("can't find .shstrtab or .strtab section");
                return NULL;
        }

        s = elf_getscn(elf->elf, shstrtab->idx);
        if (!s) {
                WARN_ELF("elf_getscn");
                return NULL;
        }

        data = elf_newdata(s);
        if (!data) {
                WARN_ELF("elf_newdata");
                return NULL;
        }

        data->d_buf = sec->name;
        data->d_size = strlen(name) + 1;
        data->d_align = 1;

        sec->sh.sh_name = shstrtab->len;

        shstrtab->len += strlen(name) + 1;
        shstrtab->changed = true;

        return sec;
}

struct section *elf_create_rela_section(struct elf *elf, struct section *base)
{
        char *relaname;
        struct section *sec;

        relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
        if (!relaname) {
                perror("malloc");
                return NULL;
        }
        strcpy(relaname, ".rela");
        strcat(relaname, base->name);

        sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
        free(relaname);
        if (!sec)
                return NULL;

        base->rela = sec;
        sec->base = base;

        sec->sh.sh_type = SHT_RELA;
        sec->sh.sh_addralign = 8;
        sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
        sec->sh.sh_info = base->idx;
        sec->sh.sh_flags = SHF_INFO_LINK;

        return sec;
}

int elf_rebuild_rela_section(struct section *sec)
{
        struct rela *rela;
        int nr, idx = 0, size;
        GElf_Rela *relas;

        nr = 0;
        list_for_each_entry(rela, &sec->rela_list, list)
                nr++;

        size = nr * sizeof(*relas);
        relas = malloc(size);
        if (!relas) {
                perror("malloc");
                return -1;
        }

        sec->data->d_buf = relas;
        sec->data->d_size = size;

        sec->sh.sh_size = size;

        idx = 0;
        list_for_each_entry(rela, &sec->rela_list, list) {
                relas[idx].r_offset = rela->offset;
                relas[idx].r_addend = rela->addend;
                relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
                idx++;
        }

        return 0;
}

int elf_write(struct elf *elf)
{
        struct section *sec;
        Elf_Scn *s;

        /* Update section headers for changed sections: */
        list_for_each_entry(sec, &elf->sections, list) {
                if (sec->changed) {
                        s = elf_getscn(elf->elf, sec->idx);
                        if (!s) {
                                WARN_ELF("elf_getscn");
                                return -1;
                        }
                        if (!gelf_update_shdr(s, &sec->sh)) {
                                WARN_ELF("gelf_update_shdr");
                                return -1;
                        }
                }
        }

        /* Make sure the new section header entries get updated properly. */
        elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);

        /* Write all changes to the file. */
        if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
                WARN_ELF("elf_update");
                return -1;
        }

        return 0;
}

void elf_close(struct elf *elf)
{
        struct section *sec, *tmpsec;
        struct symbol *sym, *tmpsym;
        struct rela *rela, *tmprela;

        if (elf->elf)
                elf_end(elf->elf);

        if (elf->fd > 0)
                close(elf->fd);

        list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
                list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
                        list_del(&sym->list);
                        hash_del(&sym->hash);
                        free(sym);
                }
                list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
                        list_del(&rela->list);
                        hash_del(&rela->hash);
                        free(rela);
                }
                list_del(&sec->list);
                free(sec);
        }

        free(elf);
}