Human-parseable symbol resolution errors

plt0.c

//Iterates each symbol that is either in .rel.dyn or .rel.plt sections
#define FOREACH_REL(func) \
    for (int i = 0; i < elf_hdr->e_shnum; i++) { \
        char *sh_name = shstrtab + sec_hdr[i].sh_name; \
        if (strcmp(sh_name, ".rel.dyn") == 0 || strcmp(sh_name, ".rel.plt") == 0) { \
            Elf32_Rel *rels = (Elf32_Rel *)((uintptr_t)text_base + sec_hdr[i].sh_addr); \
            for (size_t j = 0; j < sec_hdr[i].sh_size / sizeof(Elf32_Rel); j++) { \
                uintptr_t *ptr = (uintptr_t *)(text_base + rels[j].r_offset); \
                Elf32_Sym *sym = &syms[ELF32_R_SYM(rels[j].r_info)]; \
                int type = ELF32_R_TYPE(rels[j].r_info); \
                func \
            } \
        } \
    }
        
uintptr_t reloc_err(uintptr_t gotx)
{
    FOREACH_REL(
        switch (type) {
        case R_ARM_GLOB_DAT:
        case R_ARM_JUMP_SLOT:
            if (sym->st_shndx == SHN_UNDEF) {
                if (gotx == ptr) {
                    const char *name = dynstrtab + sym->st_name;
                    fatal_error("Undefined symbol %s.\n", name);
                    exit(-1);
                }
            }

            break;
        default:
            break;
        }
    )

    fatal_error("Unable to locate reloc %p???\n", gotx);
    exit(-1);
}

__attribute__((naked)) void plt0_stub()
{
    register uintptr_t got0 asm("r12");
    reloc_err(got0);
}

int so_relocate(void) {
    FOREACH_REL(
        const char *name = dynstrtab + sym->st_name;

        switch (type) {
        case R_ARM_ABS32:
            *ptr += (uintptr_t)text_base + sym->st_value;
            break;

        case R_ARM_RELATIVE:
            *ptr += (uintptr_t)text_base;
            break;

        case R_ARM_GLOB_DAT:
        case R_ARM_JUMP_SLOT:
        {
            if (sym->st_shndx != SHN_UNDEF)
                *ptr = (uintptr_t)text_base + sym->st_value;
            else {
                if ((*ptr = so_resolve_symbol(name)) == NULL) {
                    if (type == R_ARM_JUMP_SLOT)
                        *ptr = plt0_stub;
                    else {
                        fatal_error("Undefined symbol %s.\n", name);
                        exit(-1);
                    }
                }
            }

            break;
        }

        default:
            fatal_error("Error unknown relocation type %x\n", type);
            break;
        }
    )

    return 0;
}