// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
 */

/*
 * This file reads all the special sections which have alternate instructions
 * which can be patched in or redirected to at runtime.
 */

#include <stdlib.h>
#include <string.h>

#include <arch/special.h>
#include <objtool/builtin.h>
#include <objtool/special.h>
#include <objtool/warn.h>
#include <objtool/endianness.h>

struct special_entry {
        const char *sec;
        bool group, jump_or_nop;
        unsigned char size, orig, new;
        unsigned char orig_len, new_len; /* group only */
        unsigned char feature; /* ALTERNATIVE macro CPU feature */
        unsigned char key; /* jump_label key */
};

struct special_entry entries[] = {
        {
                .sec = ".altinstructions",
                .group = true,
                .size = ALT_ENTRY_SIZE,
                .orig = ALT_ORIG_OFFSET,
                .orig_len = ALT_ORIG_LEN_OFFSET,
                .new = ALT_NEW_OFFSET,
                .new_len = ALT_NEW_LEN_OFFSET,
                .feature = ALT_FEATURE_OFFSET,
        },
        {
                .sec = "__jump_table",
                .jump_or_nop = true,
                .size = JUMP_ENTRY_SIZE,
                .orig = JUMP_ORIG_OFFSET,
                .new = JUMP_NEW_OFFSET,
                .key = JUMP_KEY_OFFSET,
        },
        {
                .sec = "__ex_table",
                .size = EX_ENTRY_SIZE,
                .orig = EX_ORIG_OFFSET,
                .new = EX_NEW_OFFSET,
        },
        {},
};

void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)
{
}

static void reloc_to_sec_off(struct reloc *reloc, struct section **sec,
                             unsigned long *off)
{
        *sec = reloc->sym->sec;
        *off = reloc->sym->offset + reloc->addend;
}

static int get_alt_entry(struct elf *elf, struct special_entry *entry,
                         struct section *sec, int idx,
                         struct special_alt *alt)
{
        struct reloc *orig_reloc, *new_reloc;
        unsigned long offset;

        offset = idx * entry->size;

        alt->group = entry->group;
        alt->jump_or_nop = entry->jump_or_nop;

        if (alt->group) {
                alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset +
                                                   entry->orig_len);
                alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
                                                  entry->new_len);
        }

        if (entry->feature) {
                unsigned short feature;

                feature = bswap_if_needed(*(unsigned short *)(sec->data->d_buf +
                                                              offset +
                                                              entry->feature));
                arch_handle_alternative(feature, alt);
        }

        orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);
        if (!orig_reloc) {
                WARN_FUNC("can't find orig reloc", sec, offset + entry->orig);
                return -1;
        }

        reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off);

        if (!entry->group || alt->new_len) {
                new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new);
                if (!new_reloc) {
                        WARN_FUNC("can't find new reloc",
                                  sec, offset + entry->new);
                        return -1;
                }

                /*
                 * Skip retpoline .altinstr_replacement... we already rewrite the
                 * instructions for retpolines anyway, see arch_is_retpoline()
                 * usage in add_{call,jump}_destinations().
                 */
                if (arch_is_retpoline(new_reloc->sym))
                        return 1;

                reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off);

                /* _ASM_EXTABLE_EX hack */
                if (alt->new_off >= 0x7ffffff0)
                        alt->new_off -= 0x7ffffff0;
        }

        if (entry->key) {
                struct reloc *key_reloc;

                key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key);
                if (!key_reloc) {
                        WARN_FUNC("can't find key reloc",
                                  sec, offset + entry->key);
                        return -1;
                }
                alt->key_addend = key_reloc->addend;
        }

        return 0;
}

/*
 * Read all the special sections and create a list of special_alt structs which
 * describe all the alternate instructions which can be patched in or
 * redirected to at runtime.
 */
int special_get_alts(struct elf *elf, struct list_head *alts)
{
        struct special_entry *entry;
        struct section *sec;
        unsigned int nr_entries;
        struct special_alt *alt;
        int idx, ret;

        INIT_LIST_HEAD(alts);

        for (entry = entries; entry->sec; entry++) {
                sec = find_section_by_name(elf, entry->sec);
                if (!sec)
                        continue;

                if (sec->sh.sh_size % entry->size != 0) {
                        WARN("%s size not a multiple of %d",
                             sec->name, entry->size);
                        return -1;
                }

                nr_entries = sec->sh.sh_size / entry->size;

                for (idx = 0; idx < nr_entries; idx++) {
                        alt = malloc(sizeof(*alt));
                        if (!alt) {
                                WARN("malloc failed");
                                return -1;
                        }
                        memset(alt, 0, sizeof(*alt));

                        ret = get_alt_entry(elf, entry, sec, idx, alt);
                        if (ret > 0)
                                continue;
                        if (ret < 0)
                                return ret;

                        list_add_tail(&alt->list, alts);
                }
        }

        return 0;
}