/*  Kernel module help for Meta.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
*/
#include <linux/moduleloader.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/sort.h>

#include <asm/unaligned.h>

/* Count how many different relocations (different symbol, different
   addend) */
static unsigned int count_relocs(const Elf32_Rela *rela, unsigned int num)
{
        unsigned int i, r_info, r_addend, _count_relocs;

        _count_relocs = 0;
        r_info = 0;
        r_addend = 0;
        for (i = 0; i < num; i++)
                /* Only count relbranch relocs, others don't need stubs */
                if (ELF32_R_TYPE(rela[i].r_info) == R_METAG_RELBRANCH &&
                    (r_info != ELF32_R_SYM(rela[i].r_info) ||
                     r_addend != rela[i].r_addend)) {
                        _count_relocs++;
                        r_info = ELF32_R_SYM(rela[i].r_info);
                        r_addend = rela[i].r_addend;
                }

        return _count_relocs;
}

static int relacmp(const void *_x, const void *_y)
{
        const Elf32_Rela *x, *y;

        y = (Elf32_Rela *)_x;
        x = (Elf32_Rela *)_y;

        /* Compare the entire r_info (as opposed to ELF32_R_SYM(r_info) only) to
         * make the comparison cheaper/faster. It won't affect the sorting or
         * the counting algorithms' performance
         */
        if (x->r_info < y->r_info)
                return -1;
        else if (x->r_info > y->r_info)
                return 1;
        else if (x->r_addend < y->r_addend)
                return -1;
        else if (x->r_addend > y->r_addend)
                return 1;
        else
                return 0;
}

static void relaswap(void *_x, void *_y, int size)
{
        uint32_t *x, *y, tmp;
        int i;

        y = (uint32_t *)_x;
        x = (uint32_t *)_y;

        for (i = 0; i < sizeof(Elf32_Rela) / sizeof(uint32_t); i++) {
                tmp = x[i];
                x[i] = y[i];
                y[i] = tmp;
        }
}

/* Get the potential trampolines size required of the init and
   non-init sections */
static unsigned long get_plt_size(const Elf32_Ehdr *hdr,
                                  const Elf32_Shdr *sechdrs,
                                  const char *secstrings,
                                  int is_init)
{
        unsigned long ret = 0;
        unsigned i;

        /* Everything marked ALLOC (this includes the exported
           symbols) */
        for (i = 1; i < hdr->e_shnum; i++) {
                /* If it's called *.init*, and we're not init, we're
                   not interested */
                if ((strstr(secstrings + sechdrs[i].sh_name, ".init") != NULL)
                    != is_init)
                        continue;

                /* We don't want to look at debug sections. */
                if (strstr(secstrings + sechdrs[i].sh_name, ".debug") != NULL)
                        continue;

                if (sechdrs[i].sh_type == SHT_RELA) {
                        pr_debug("Found relocations in section %u\n", i);
                        pr_debug("Ptr: %p.  Number: %u\n",
                                 (void *)hdr + sechdrs[i].sh_offset,
                                 sechdrs[i].sh_size / sizeof(Elf32_Rela));

                        /* Sort the relocation information based on a symbol and
                         * addend key. This is a stable O(n*log n) complexity
                         * alogrithm but it will reduce the complexity of
                         * count_relocs() to linear complexity O(n)
                         */
                        sort((void *)hdr + sechdrs[i].sh_offset,
                             sechdrs[i].sh_size / sizeof(Elf32_Rela),
                             sizeof(Elf32_Rela), relacmp, relaswap);

                        ret += count_relocs((void *)hdr
                                             + sechdrs[i].sh_offset,
                                             sechdrs[i].sh_size
                                             / sizeof(Elf32_Rela))
                                * sizeof(struct metag_plt_entry);
                }
        }

        return ret;
}

int module_frob_arch_sections(Elf32_Ehdr *hdr,
                              Elf32_Shdr *sechdrs,
                              char *secstrings,
                              struct module *me)
{
        unsigned int i;

        /* Find .plt and .init.plt sections */
        for (i = 0; i < hdr->e_shnum; i++) {
                if (strcmp(secstrings + sechdrs[i].sh_name, ".init.plt") == 0)
                        me->arch.init_plt_section = i;
                else if (strcmp(secstrings + sechdrs[i].sh_name, ".plt") == 0)
                        me->arch.core_plt_section = i;
        }
        if (!me->arch.core_plt_section || !me->arch.init_plt_section) {
                pr_err("Module doesn't contain .plt or .init.plt sections.\n");
                return -ENOEXEC;
        }

        /* Override their sizes */
        sechdrs[me->arch.core_plt_section].sh_size
                = get_plt_size(hdr, sechdrs, secstrings, 0);
        sechdrs[me->arch.core_plt_section].sh_type = SHT_NOBITS;
        sechdrs[me->arch.init_plt_section].sh_size
                = get_plt_size(hdr, sechdrs, secstrings, 1);
        sechdrs[me->arch.init_plt_section].sh_type = SHT_NOBITS;
        return 0;
}

/* Set up a trampoline in the PLT to bounce us to the distant function */
static uint32_t do_plt_call(void *location, Elf32_Addr val,
                            Elf32_Shdr *sechdrs, struct module *mod)
{
        struct metag_plt_entry *entry;
        /* Instructions used to do the indirect jump.  */
        uint32_t tramp[2];

        /* We have to trash a register, so we assume that any control
           transfer more than 21-bits away must be a function call
           (so we can use a call-clobbered register).  */

        /* MOVT D0Re0,#HI(v) */
        tramp[0] = 0x02000005 | (((val & 0xffff0000) >> 16) << 3);
        /* JUMP D0Re0,#LO(v) */
        tramp[1] = 0xac000001 | ((val & 0x0000ffff) << 3);

        /* Init, or core PLT? */
        if (location >= mod->module_core
            && location < mod->module_core + mod->core_size)
                entry = (void *)sechdrs[mod->arch.core_plt_section].sh_addr;
        else
                entry = (void *)sechdrs[mod->arch.init_plt_section].sh_addr;

        /* Find this entry, or if that fails, the next avail. entry */
        while (entry->tramp[0])
                if (entry->tramp[0] == tramp[0] && entry->tramp[1] == tramp[1])
                        return (uint32_t)entry;
                else
                        entry++;

        entry->tramp[0] = tramp[0];
        entry->tramp[1] = tramp[1];

        return (uint32_t)entry;
}

int apply_relocate_add(Elf32_Shdr *sechdrs,
                   const char *strtab,
                   unsigned int symindex,
                   unsigned int relsec,
                   struct module *me)
{
        unsigned int i;
        Elf32_Rela *rel = (void *)sechdrs[relsec].sh_addr;
        Elf32_Sym *sym;
        Elf32_Addr relocation;
        uint32_t *location;
        int32_t value;

        pr_debug("Applying relocate section %u to %u\n", relsec,
                 sechdrs[relsec].sh_info);
        for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
                /* This is where to make the change */
                location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
                        + rel[i].r_offset;
                /* This is the symbol it is referring to.  Note that all
                   undefined symbols have been resolved.  */
                sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
                        + ELF32_R_SYM(rel[i].r_info);
                relocation = sym->st_value + rel[i].r_addend;

                switch (ELF32_R_TYPE(rel[i].r_info)) {
                case R_METAG_NONE:
                        break;
                case R_METAG_HIADDR16:
                        relocation >>= 16;
                case R_METAG_LOADDR16:
                        *location = (*location & 0xfff80007) |
                                ((relocation & 0xffff) << 3);
                        break;
                case R_METAG_ADDR32:
                        /*
                         * Packed data structures may cause a misaligned
                         * R_METAG_ADDR32 to be emitted.
                         */
                        put_unaligned(relocation, location);
                        break;
                case R_METAG_GETSETOFF:
                        *location += ((relocation & 0xfff) << 7);
                        break;
                case R_METAG_RELBRANCH:
                        if (*location & (0x7ffff << 5)) {
                                pr_err("bad relbranch relocation\n");
                                break;
                        }

                        /* This jump is too big for the offset slot. Build
                         * a PLT to jump through to get to where we want to go.
                         * NB: 21bit check - not scaled to 19bit yet
                         */
                        if (((int32_t)(relocation -
                                       (uint32_t)location) > 0xfffff) ||
                            ((int32_t)(relocation -
                                       (uint32_t)location) < -0xfffff)) {
                                relocation = do_plt_call(location, relocation,
                                                         sechdrs, me);
                        }

                        value = relocation - (uint32_t)location;

                        /* branch instruction aligned */
                        value /= 4;

                        if ((value > 0x7ffff) || (value < -0x7ffff)) {
                                /*
                                 * this should have been caught by the code
                                 * above!
                                 */
                                pr_err("overflow of relbranch reloc\n");
                        }

                        *location = (*location & (~(0x7ffff << 5))) |
                                ((value & 0x7ffff) << 5);
                        break;

                default:
                        pr_err("module %s: Unknown relocation: %u\n",
                               me->name, ELF32_R_TYPE(rel[i].r_info));
                        return -ENOEXEC;
                }
        }
        return 0;
}