outelf.c

nasm的全套源代码,有些我做了些修改,以方便您更方便更容易调试成功,方便学习做编译器

            type = SHT_PROGBITS;
        } else if (!nasm_stricmp(q, "nobits")) {
            type = SHT_NOBITS;
        }
    }

    if (!strcmp(name, ".comment") ||
        !strcmp(name, ".shstrtab") ||
        !strcmp(name, ".symtab") || !strcmp(name, ".strtab")) {
        error(ERR_NONFATAL, "attempt to redefine reserved section"
              "name `%s'", name);
        return NO_SEG;
    }

    for (i = 0; i < nsects; i++)
        if (!strcmp(name, sects[i]->name))
            break;
    if (i == nsects) {
        if (!strcmp(name, ".text"))
            i = elf_make_section(name, SHT_PROGBITS,
                                 SHF_ALLOC | SHF_EXECINSTR, 16);
        else if (!strcmp(name, ".rodata"))
            i = elf_make_section(name, SHT_PROGBITS, SHF_ALLOC, 4);
        else if (!strcmp(name, ".data"))
            i = elf_make_section(name, SHT_PROGBITS,
                                 SHF_ALLOC | SHF_WRITE, 4);
        else if (!strcmp(name, ".bss"))
            i = elf_make_section(name, SHT_NOBITS,
                                 SHF_ALLOC | SHF_WRITE, 4);
        else
            i = elf_make_section(name, SHT_PROGBITS, SHF_ALLOC, 1);
        if (type)
            sects[i]->type = type;
        if (align)
            sects[i]->align = align;
        sects[i]->flags &= ~flags_and;
        sects[i]->flags |= flags_or;
    } else if (pass == 1) {
        if (type || align || flags_and)
            error(ERR_WARNING, "section attributes ignored on"
                  " redeclaration of section `%s'", name);
    }

    return sects[i]->index;
}

static void elf_deflabel(char *name, long segment, long offset,
                         int is_global, char *special)
{
    int pos = strslen;
    struct Symbol *sym;
    int special_used = FALSE;

#if defined(DEBUG) && DEBUG>2
    fprintf(stderr,
            " elf_deflabel: %s, seg=%ld, off=%ld, is_global=%d, %s\n",
            name, segment, offset, is_global, special);
#endif
    if (name[0] == '.' && name[1] == '.' && name[2] != '@') {
        /*
         * This is a NASM special symbol. We never allow it into
         * the ELF symbol table, even if it's a valid one. If it
         * _isn't_ a valid one, we should barf immediately.
         */
        if (strcmp(name, "..gotpc") && strcmp(name, "..gotoff") &&
            strcmp(name, "..got") && strcmp(name, "..plt") &&
            strcmp(name, "..sym"))
            error(ERR_NONFATAL, "unrecognised special symbol `%s'", name);
        return;
    }

    if (is_global == 3) {
        struct Symbol **s;
        /*
         * Fix up a forward-reference symbol size from the first
         * pass.
         */
        for (s = &fwds; *s; s = &(*s)->nextfwd)
            if (!strcmp((*s)->name, name)) {
                struct tokenval tokval;
                expr *e;
                char *p = special;

                while (*p && !isspace(*p))
                    p++;
                while (*p && isspace(*p))
                    p++;
                stdscan_reset();
                stdscan_bufptr = p;
                tokval.t_type = TOKEN_INVALID;
                e = evaluate(stdscan, NULL, &tokval, NULL, 1, error, NULL);
                if (e) {
                    if (!is_simple(e))
                        error(ERR_NONFATAL, "cannot use relocatable"
                              " expression as symbol size");
                    else
                        (*s)->size = reloc_value(e);
                }

                /*
                 * Remove it from the list of unresolved sizes.
                 */
                nasm_free((*s)->name);
                *s = (*s)->nextfwd;
                return;
            }
        return;                 /* it wasn't an important one */
    }

    saa_wbytes(strs, name, (long)(1 + strlen(name)));
    strslen += 1 + strlen(name);

    sym = saa_wstruct(syms);

    sym->strpos = pos;
    sym->type = is_global ? SYM_GLOBAL : 0;
    sym->size = 0;
    if (segment == NO_SEG)
        sym->section = SHN_ABS;
    else {
        int i;
        sym->section = SHN_UNDEF;
        if (nsects == 0 && segment == def_seg) {
            int tempint;
            if (segment != elf_section_names(".text", 2, &tempint))
                error(ERR_PANIC,
                      "strange segment conditions in ELF driver");
            sym->section = nsects;
        } else {
            for (i = 0; i < nsects; i++)
                if (segment == sects[i]->index) {
                    sym->section = i + 1;
                    break;
                }
        }
    }

    if (is_global == 2) {
        sym->size = offset;
        sym->value = 0;
        sym->section = SHN_COMMON;
        /*
         * We have a common variable. Check the special text to see
         * if it's a valid number and power of two; if so, store it
         * as the alignment for the common variable.
         */
        if (special) {
            int err;
            sym->value = readnum(special, &err);
            if (err)
                error(ERR_NONFATAL, "alignment constraint `%s' is not a"
                      " valid number", special);
            else if ((sym->value | (sym->value - 1)) != 2 * sym->value - 1)
                error(ERR_NONFATAL, "alignment constraint `%s' is not a"
                      " power of two", special);
        }
        special_used = TRUE;
    } else
        sym->value = (sym->section == SHN_UNDEF ? 0 : offset);

    if (sym->type == SYM_GLOBAL) {
        /*
         * There's a problem here that needs fixing.
         * If sym->section == SHN_ABS, then the first line of the
         * else section causes a core dump, because its a reference
         * beyond the end of the section array.
         * This behaviour is exhibited by this code:
         *     GLOBAL crash_nasm
         *     crash_nasm equ 0
         *
         * I'm not sure how to procede, because I haven't got the
         * first clue about how ELF works, so I don't know what to
         * do with it. Furthermore, I'm not sure what the rest of this
         * section of code does. Help?
         *
         * For now, I'll see if doing absolutely nothing with it will
         * work...
         */
        if (sym->section == SHN_UNDEF || sym->section == SHN_COMMON) {
            bsym = raa_write(bsym, segment, nglobs);
        } else if (sym->section != SHN_ABS) {
            /*
             * This is a global symbol; so we must add it to the linked
             * list of global symbols in its section. We'll push it on
             * the beginning of the list, because it doesn't matter
             * much which end we put it on and it's easier like this.
             *
             * In addition, we check the special text for symbol
             * type and size information.
             */
            sym->next = sects[sym->section - 1]->gsyms;
            sects[sym->section - 1]->gsyms = sym;

            if (special) {
                int n = strcspn(special, " ");

                if (!nasm_strnicmp(special, "function", n))
                    sym->type |= SYM_FUNCTION;
                else if (!nasm_strnicmp(special, "data", n) ||
                         !nasm_strnicmp(special, "object", n))
                    sym->type |= SYM_DATA;
                else
                    error(ERR_NONFATAL, "unrecognised symbol type `%.*s'",
                          n, special);
                if (special[n]) {
                    struct tokenval tokval;
                    expr *e;
                    int fwd = FALSE;
                    char *saveme = stdscan_bufptr;      /* bugfix? fbk 8/10/00 */

                    while (special[n] && isspace(special[n]))
                        n++;
                    /*
                     * We have a size expression; attempt to
                     * evaluate it.
                     */
                    stdscan_reset();
                    stdscan_bufptr = special + n;
                    tokval.t_type = TOKEN_INVALID;
                    e = evaluate(stdscan, NULL, &tokval, &fwd, 0, error,
                                 NULL);
                    if (fwd) {
                        sym->nextfwd = fwds;
                        fwds = sym;
                        sym->name = nasm_strdup(name);
                    } else if (e) {
                        if (!is_simple(e))
                            error(ERR_NONFATAL, "cannot use relocatable"
                                  " expression as symbol size");
                        else
                            sym->size = reloc_value(e);
                    }
                    stdscan_bufptr = saveme;    /* bugfix? fbk 8/10/00 */
                }
                special_used = TRUE;
            }
        }
        sym->globnum = nglobs;
        nglobs++;
    } else
        nlocals++;

    if (special && !special_used)
        error(ERR_NONFATAL, "no special symbol features supported here");
}

static void elf_add_reloc(struct Section *sect, long segment, int type)
{
    struct Reloc *r;

    r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
    sect->tail = &r->next;
    r->next = NULL;

    r->address = sect->len;
    if (segment == NO_SEG)
        r->symbol = 2;
    else {
        int i;
        r->symbol = 0;
        for (i = 0; i < nsects; i++)
            if (segment == sects[i]->index)
                r->symbol = i + 3;
        if (!r->symbol)
            r->symbol = GLOBAL_TEMP_BASE + raa_read(bsym, segment);
    }
    r->type = type;

    sect->nrelocs++;
}

/*
 * This routine deals with ..got and ..sym relocations: the more
 * complicated kinds. In shared-library writing, some relocations
 * with respect to global symbols must refer to the precise symbol
 * rather than referring to an offset from the base of the section
 * _containing_ the symbol. Such relocations call to this routine,
 * which searches the symbol list for the symbol in question.
 *
 * R_386_GOT32 references require the _exact_ symbol address to be
 * used; R_386_32 references can be at an offset from the symbol.
 * The boolean argument `exact' tells us this.
 *
 * Return value is the adjusted value of `addr', having become an
 * offset from the symbol rather than the section. Should always be
 * zero when returning from an exact call.
 *
 * Limitation: if you define two symbols at the same place,
 * confusion will occur.
 *
 * Inefficiency: we search, currently, using a linked list which
 * isn't even necessarily sorted.
 */
static long elf_add_gsym_reloc(struct Section *sect,
                               long segment, long offset,
                               int type, int exact)
{
    struct Reloc *r;
    struct Section *s;
    struct Symbol *sym, *sm;
    int i;

    /*
     * First look up the segment/offset pair and find a global
     * symbol corresponding to it. If it's not one of our segments,
     * then it must be an external symbol, in which case we're fine
     * doing a normal elf_add_reloc after first sanity-checking
     * that the offset from the symbol is zero.
     */
    s = NULL;
    for (i = 0; i < nsects; i++)
        if (segment == sects[i]->index) {
            s = sects[i];
            break;
        }
    if (!s) {
        if (exact && offset != 0)
            error(ERR_NONFATAL, "unable to find a suitable global symbol"
                  " for this reference");
        else
            elf_add_reloc(sect, segment, type);
        return offset;
    }

    if (exact) {
        /*
         * Find a symbol pointing _exactly_ at this one.
         */
        for (sym = s->gsyms; sym; sym = sym->next)
            if (sym->value == offset)
                break;
    } else {
        /*
         * Find the nearest symbol below this one.
         */
        sym = NULL;
        for (sm = s->gsyms; sm; sm = sm->next)
            if (sm->value <= offset && (!sym || sm->value > sym->value))
                sym = sm;
    }
    if (!sym && exact) {
        error(ERR_NONFATAL, "unable to find a suitable global symbol"
              " for this reference");
        return 0;
    }

    r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
    sect->tail = &r->next;
    r->next = NULL;

    r->address = sect->len;
    r->symbol = GLOBAL_TEMP_BASE + sym->globnum;
    r->type = type;

    sect->nrelocs++;

    return offset - sym->value;
}

static void elf_out(long segto, const void *data, unsigned long type,
                    long segment, long wrt)
{
    struct Section *s;
    long realbytes = type & OUT_SIZMASK;
    long addr;
    unsigned char mydata[4], *p;
    int i;
    static struct symlininfo sinfo;

    type &= OUT_TYPMASK;

    /*
     * handle absolute-assembly (structure definitions)
     */
    if (segto == NO_SEG) {
        if (type != OUT_RESERVE)
            error(ERR_NONFATAL, "attempt to assemble code in [ABSOLUTE]"
                  " space");
        return;