/*
 * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>

#include <asm/cache.h>
#include <asm/opcodes.h>

#define PLT_ENT_STRIDE          L1_CACHE_BYTES
#define PLT_ENT_COUNT           (PLT_ENT_STRIDE / sizeof(u32))
#define PLT_ENT_SIZE            (sizeof(struct plt_entries) / PLT_ENT_COUNT)

#ifdef CONFIG_THUMB2_KERNEL
#define PLT_ENT_LDR             __opcode_to_mem_thumb32(0xf8dff000 | \
                                                        (PLT_ENT_STRIDE - 4))
#else
#define PLT_ENT_LDR             __opcode_to_mem_arm(0xe59ff000 | \
                                                    (PLT_ENT_STRIDE - 8))
#endif

struct plt_entries {
        u32     ldr[PLT_ENT_COUNT];
        u32     lit[PLT_ENT_COUNT];
};

static bool in_init(const struct module *mod, unsigned long loc)
{
        return loc - (u32)mod->init_layout.base < mod->init_layout.size;
}

u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
        struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
                                                          &mod->arch.init;

        struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
        int idx = 0;

        /*
         * Look for an existing entry pointing to 'val'. Given that the
         * relocations are sorted, this will be the last entry we allocated.
         * (if one exists).
         */
        if (pltsec->plt_count > 0) {
                plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
                idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;

                if (plt->lit[idx] == val)
                        return (u32)&plt->ldr[idx];

                idx = (idx + 1) % PLT_ENT_COUNT;
                if (!idx)
                        plt++;
        }

        pltsec->plt_count++;
        BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);

        if (!idx)
                /* Populate a new set of entries */
                *plt = (struct plt_entries){
                        { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
                        { val, }
                };
        else
                plt->lit[idx] = val;

        return (u32)&plt->ldr[idx];
}

#define cmp_3way(a,b)   ((a) < (b) ? -1 : (a) > (b))

static int cmp_rel(const void *a, const void *b)
{
        const Elf32_Rel *x = a, *y = b;
        int i;

        /* sort by type and symbol index */
        i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
        if (i == 0)
                i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
        return i;
}

static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
{
        u32 *tval = (u32 *)(base + rel->r_offset);

        /*
         * Do a bitwise compare on the raw addend rather than fully decoding
         * the offset and doing an arithmetic comparison.
         * Note that a zero-addend jump/call relocation is encoded taking the
         * PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
         */
        switch (ELF32_R_TYPE(rel->r_info)) {
                u16 upper, lower;

        case R_ARM_THM_CALL:
        case R_ARM_THM_JUMP24:
                upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
                lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);

                return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;

        case R_ARM_CALL:
        case R_ARM_PC24:
        case R_ARM_JUMP24:
                return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
        }
        BUG();
}

static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
{
        const Elf32_Rel *prev;

        /*
         * Entries are sorted by type and symbol index. That means that,
         * if a duplicate entry exists, it must be in the preceding
         * slot.
         */
        if (!num)
                return false;

        prev = rel + num - 1;
        return cmp_rel(rel + num, prev) == 0 &&
               is_zero_addend_relocation(base, prev);
}

/* Count how many PLT entries we may need */
static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
                               const Elf32_Rel *rel, int num, Elf32_Word dstidx)
{
        unsigned int ret = 0;
        const Elf32_Sym *s;
        int i;

        for (i = 0; i < num; i++) {
                switch (ELF32_R_TYPE(rel[i].r_info)) {
                case R_ARM_CALL:
                case R_ARM_PC24:
                case R_ARM_JUMP24:
                case R_ARM_THM_CALL:
                case R_ARM_THM_JUMP24:
                        /*
                         * We only have to consider branch targets that resolve
                         * to symbols that are defined in a different section.
                         * This is not simply a heuristic, it is a fundamental
                         * limitation, since there is no guaranteed way to emit
                         * PLT entries sufficiently close to the branch if the
                         * section size exceeds the range of a branch
                         * instruction. So ignore relocations against defined
                         * symbols if they live in the same section as the
                         * relocation target.
                         */
                        s = syms + ELF32_R_SYM(rel[i].r_info);
                        if (s->st_shndx == dstidx)
                                break;

                        /*
                         * Jump relocations with non-zero addends against
                         * undefined symbols are supported by the ELF spec, but
                         * do not occur in practice (e.g., 'jump n bytes past
                         * the entry point of undefined function symbol f').
                         * So we need to support them, but there is no need to
                         * take them into consideration when trying to optimize
                         * this code. So let's only check for duplicates when
                         * the addend is zero. (Note that calls into the core
                         * module via init PLT entries could involve section
                         * relative symbol references with non-zero addends, for
                         * which we may end up emitting duplicates, but the init
                         * PLT is released along with the rest of the .init
                         * region as soon as module loading completes.)
                         */
                        if (!is_zero_addend_relocation(base, rel + i) ||
                            !duplicate_rel(base, rel, i))
                                ret++;
                }
        }
        return ret;
}

int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
                              char *secstrings, struct module *mod)
{
        unsigned long core_plts = 0;
        unsigned long init_plts = 0;
        Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
        Elf32_Sym *syms = NULL;

        /*
         * To store the PLTs, we expand the .text section for core module code
         * and for initialization code.
         */
        for (s = sechdrs; s < sechdrs_end; ++s) {
                if (strcmp(".plt", secstrings + s->sh_name) == 0)
                        mod->arch.core.plt = s;
                else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
                        mod->arch.init.plt = s;
                else if (s->sh_type == SHT_SYMTAB)
                        syms = (Elf32_Sym *)s->sh_addr;
        }

        if (!mod->arch.core.plt || !mod->arch.init.plt) {
                pr_err("%s: module PLT section(s) missing\n", mod->name);
                return -ENOEXEC;
        }
        if (!syms) {
                pr_err("%s: module symtab section missing\n", mod->name);
                return -ENOEXEC;
        }

        for (s = sechdrs + 1; s < sechdrs_end; ++s) {
                Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
                int numrels = s->sh_size / sizeof(Elf32_Rel);
                Elf32_Shdr *dstsec = sechdrs + s->sh_info;

                if (s->sh_type != SHT_REL)
                        continue;

                /* ignore relocations that operate on non-exec sections */
                if (!(dstsec->sh_flags & SHF_EXECINSTR))
                        continue;

                /* sort by type and symbol index */
                sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);

                if (strncmp(secstrings + dstsec->sh_name, ".init", 5) != 0)
                        core_plts += count_plts(syms, dstsec->sh_addr, rels,
                                                numrels, s->sh_info);
                else
                        init_plts += count_plts(syms, dstsec->sh_addr, rels,
                                                numrels, s->sh_info);
        }

        mod->arch.core.plt->sh_type = SHT_NOBITS;
        mod->arch.core.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
        mod->arch.core.plt->sh_addralign = L1_CACHE_BYTES;
        mod->arch.core.plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
                                               sizeof(struct plt_entries));
        mod->arch.core.plt_count = 0;

        mod->arch.init.plt->sh_type = SHT_NOBITS;
        mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
        mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES;
        mod->arch.init.plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
                                               sizeof(struct plt_entries));
        mod->arch.init.plt_count = 0;

        pr_debug("%s: plt=%x, init.plt=%x\n", __func__,
                 mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
        return 0;
}