module.c

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#include <linux/moduleloader.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>

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

int apply_relocate_add(Elf32_Shdr *sechdrs,
               const char *strtab,
               unsigned int symindex,
               unsigned int relsec,
               struct module *me)
{
    unsigned int i;
    Elf32_Rela *rela = (void *)sechdrs[relsec].sh_addr;

    DEBUGP("Applying relocate section %u to %u\n", relsec,
           sechdrs[relsec].sh_info);
    for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
        /* This is where to make the change */
        uint32_t *loc = (uint32_t *)(sechdrs[sechdrs[relsec].sh_info].sh_addr
                         + rela[i].r_offset);
        /* This is the symbol it is referring to.  Note that all
           undefined symbols have been resolved.  */
        Elf32_Sym *sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
            + ELF32_R_SYM(rela[i].r_info);
        uint32_t v = sym->st_value + rela[i].r_addend;

        switch (ELF32_R_TYPE(rela[i].r_info)) {
        case R_H8_DIR24R8:
            loc = (uint32_t *)((uint32_t)loc - 1);
            *loc = (*loc & 0xff000000) | ((*loc & 0xffffff) + v);
            break;
        case R_H8_DIR24A8:
            if (ELF32_R_SYM(rela[i].r_info))
                *loc += v;
            break;
        case R_H8_DIR32:
        case R_H8_DIR32A16:
            *loc += v;
            break;
        case R_H8_PCREL16:
            v -= (unsigned long)loc + 2;
            if ((Elf32_Sword)v > 0x7fff || 
                (Elf32_Sword)v < -(Elf32_Sword)0x8000)
                goto overflow;
            else 
                *(unsigned short *)loc = v;
            break;
        case R_H8_PCREL8:
            v -= (unsigned long)loc + 1;
            if ((Elf32_Sword)v > 0x7f || 
                (Elf32_Sword)v < -(Elf32_Sword)0x80)
                goto overflow;
            else 
                *(unsigned char *)loc = v;
            break;
        default:
            printk(KERN_ERR "module %s: Unknown relocation: %u\n",
                   me->name, ELF32_R_TYPE(rela[i].r_info));
            return -ENOEXEC;
        }
    }
    return 0;
 overflow:
    printk(KERN_ERR "module %s: relocation offset overflow: %08x\n",
           me->name, rela[i].r_offset);
    return -ENOEXEC;
}