module.c

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/*  Kernel module help for Alpha.
    Copyright (C) 2002 Richard Henderson.

    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.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#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/slab.h>

#if 0
#define DEBUGP printk
#else
#define DEBUGP(fmt...)
#endif

/* Allocate the GOT at the end of the core sections.  */

struct got_entry {
    struct got_entry *next;
    Elf64_Sxword r_addend;
    int got_offset;
};

static inline void
process_reloc_for_got(Elf64_Rela *rela,
              struct got_entry *chains, Elf64_Xword *poffset)
{
    unsigned long r_sym = ELF64_R_SYM (rela->r_info);
    unsigned long r_type = ELF64_R_TYPE (rela->r_info);
    Elf64_Sxword r_addend = rela->r_addend;
    struct got_entry *g;

    if (r_type != R_ALPHA_LITERAL)
        return;

    for (g = chains + r_sym; g ; g = g->next)
        if (g->r_addend == r_addend) {
            if (g->got_offset == 0) {
                g->got_offset = *poffset;
                *poffset += 8;
            }
            goto found_entry;
        }

    g = kmalloc (sizeof (*g), GFP_KERNEL);
    g->next = chains[r_sym].next;
    g->r_addend = r_addend;
    g->got_offset = *poffset;
    *poffset += 8;
    chains[r_sym].next = g;

 found_entry:
    /* Trick: most of the ELF64_R_TYPE field is unused.  There are
       42 valid relocation types, and a 32-bit field.  Co-opt the
       bits above 256 to store the got offset for this reloc.  */
    rela->r_info |= g->got_offset << 8;
}

int
module_frob_arch_sections(Elf64_Ehdr *hdr, Elf64_Shdr *sechdrs,
              char *secstrings, struct module *me)
{
    struct got_entry *chains;
    Elf64_Rela *rela;
    Elf64_Shdr *esechdrs, *symtab, *s, *got;
    unsigned long nsyms, nrela, i;

    esechdrs = sechdrs + hdr->e_shnum;
    symtab = got = NULL;

    /* Find out how large the symbol table is.  Allocate one got_entry
       head per symbol.  Normally this will be enough, but not always.
       We'll chain different offsets for the symbol down each head.  */
    for (s = sechdrs; s < esechdrs; ++s)
        if (s->sh_type == SHT_SYMTAB)
            symtab = s;
        else if (!strcmp(".got", secstrings + s->sh_name)) {
            got = s;
            me->arch.gotsecindex = s - sechdrs;
        }

    if (!symtab) {
        printk(KERN_ERR "module %s: no symbol table\n", me->name);
        return -ENOEXEC;
    }
    if (!got) {
        printk(KERN_ERR "module %s: no got section\n", me->name);
        return -ENOEXEC;
    }

    nsyms = symtab->sh_size / sizeof(Elf64_Sym);
    chains = kcalloc(nsyms, sizeof(struct got_entry), GFP_KERNEL);
    if (!chains) {
        printk(KERN_ERR
               "module %s: no memory for symbol chain buffer\n",
               me->name);
        return -ENOMEM;
    }

    got->sh_size = 0;
    got->sh_addralign = 8;
    got->sh_type = SHT_NOBITS;

    /* Examine all LITERAL relocations to find out what GOT entries
       are required.  This sizes the GOT section as well.  */
    for (s = sechdrs; s < esechdrs; ++s)
        if (s->sh_type == SHT_RELA) {
            nrela = s->sh_size / sizeof(Elf64_Rela);
            rela = (void *)hdr + s->sh_offset;
            for (i = 0; i < nrela; ++i)
                process_reloc_for_got(rela+i, chains,
                              &got->sh_size);
        }

    /* Free the memory we allocated.  */
    for (i = 0; i < nsyms; ++i) {
        struct got_entry *g, *n;
        for (g = chains[i].next; g ; g = n) {
            n = g->next;
            kfree(g);
        }
    }
    kfree(chains);

    return 0;
}

int
apply_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
           unsigned int symindex, unsigned int relsec,
           struct module *me)
{
    Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
    unsigned long i, n = sechdrs[relsec].sh_size / sizeof(*rela);
    Elf64_Sym *symtab, *sym;
    void *base, *location;
    unsigned long got, gp;

    DEBUGP("Applying relocate section %u to %u\n", relsec,
           sechdrs[relsec].sh_info);

    base = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr;
    symtab = (Elf64_Sym *)sechdrs[symindex].sh_addr;

    /* The small sections were sorted to the end of the segment.
       The following should definitely cover them.  */
    gp = (u64)me->module_core + me->core_size - 0x8000;
    got = sechdrs[me->arch.gotsecindex].sh_addr;

    for (i = 0; i < n; i++) {
        unsigned long r_sym = ELF64_R_SYM (rela[i].r_info);
        unsigned long r_type = ELF64_R_TYPE (rela[i].r_info);
        unsigned long r_got_offset = r_type >> 8;
        unsigned long value, hi, lo;
        r_type &= 0xff;

        /* This is where to make the change.  */
        location = base + rela[i].r_offset;

        /* This is the symbol it is referring to.  Note that all
           unresolved symbols have been resolved.  */
        sym = symtab + r_sym;
        value = sym->st_value + rela[i].r_addend;

        switch (r_type) {
        case R_ALPHA_NONE:
            break;
        case R_ALPHA_REFQUAD:
            /* BUG() can produce misaligned relocations. */
            ((u32 *)location)[0] = value;
            ((u32 *)location)[1] = value >> 32;
            break;
        case R_ALPHA_GPREL32:
            value -= gp;
            if ((int)value != value)
                goto reloc_overflow;
            *(u32 *)location = value;
            break;
        case R_ALPHA_LITERAL:
            hi = got + r_got_offset;
            lo = hi - gp;
            if ((short)lo != lo)
                goto reloc_overflow;
            *(u16 *)location = lo;
            *(u64 *)hi = value;
            break;
        case R_ALPHA_LITUSE:
            break;
        case R_ALPHA_GPDISP:
            value = gp - (u64)location;
            lo = (short)value;
            hi = (int)(value - lo);
            if (hi + lo != value)
                goto reloc_overflow;
            *(u16 *)location = hi >> 16;
            *(u16 *)(location + rela[i].r_addend) = lo;
            break;
        case R_ALPHA_BRSGP:
            /* BRSGP is only allowed to bind to local symbols.
               If the section is undef, this means that the
               value was resolved from somewhere else.  */
            if (sym->st_shndx == SHN_UNDEF)
                goto reloc_overflow;
            if ((sym->st_other & STO_ALPHA_STD_GPLOAD) ==
                STO_ALPHA_STD_GPLOAD)
                /* Omit the prologue. */
                value += 8;
            /* FALLTHRU */
        case R_ALPHA_BRADDR:
            value -= (u64)location + 4;
            if (value & 3)
                goto reloc_overflow;
            value = (long)value >> 2;
            if (value + (1<<21) >= 1<<22)
                goto reloc_overflow;
            value &= 0x1fffff;
            value |= *(u32 *)location & ~0x1fffff;
            *(u32 *)location = value;
            break;
        case R_ALPHA_HINT:
            break;
        case R_ALPHA_SREL32:
            value -= (u64)location;
            if ((int)value != value)
                goto reloc_overflow;
            *(u32 *)location = value;
            break;
        case R_ALPHA_SREL64:
            value -= (u64)location;
            *(u64 *)location = value;
            break;
        case R_ALPHA_GPRELHIGH:
            value = (long)(value - gp + 0x8000) >> 16;
            if ((short) value != value)
                goto reloc_overflow;
            *(u16 *)location = value;
            break;
        case R_ALPHA_GPRELLOW:
            value -= gp;
            *(u16 *)location = value;
            break;
        case R_ALPHA_GPREL16:
            value -= gp;
            if ((short) value != value)
                goto reloc_overflow;
            *(u16 *)location = value;
            break;
        default:
            printk(KERN_ERR "module %s: Unknown relocation: %lu\n",
                   me->name, r_type);
            return -ENOEXEC;
        reloc_overflow:
            if (ELF64_ST_TYPE (sym->st_info) == STT_SECTION)
              printk(KERN_ERR
                     "module %s: Relocation (type %lu) overflow vs section %d\n",
                     me->name, r_type, sym->st_shndx);
            else
              printk(KERN_ERR
                     "module %s: Relocation (type %lu) overflow vs %s\n",
                     me->name, r_type, strtab + sym->st_name);
            return -ENOEXEC;
        }
    }

    return 0;
}