outaout.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

/* outaout.c	output routines for the Netwide Assembler to produce
 *		Linux a.out object files
 *
 * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
 * Julian Hall. All rights reserved. The software is
 * redistributable under the licence given in the file "Licence"
 * distributed in the NASM archive.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#include "nasm.h"
#include "nasmlib.h"
#include "outform.h"

#if defined OF_AOUT || defined OF_AOUTB

#define RELTYPE_ABSOLUTE 0x00
#define RELTYPE_RELATIVE 0x01
#define RELTYPE_GOTPC    0x01   /* no explicit GOTPC in a.out */
#define RELTYPE_GOTOFF   0x10
#define RELTYPE_GOT      0x10   /* distinct from GOTOFF bcos sym not sect */
#define RELTYPE_PLT      0x21
#define RELTYPE_SYMFLAG  0x08

struct Reloc {
    struct Reloc *next;
    long address;               /* relative to _start_ of section */
    long symbol;                /* symbol number or -ve section id */
    int bytes;                  /* 2 or 4 */
    int reltype;                /* see above */
};

struct Symbol {
    long strpos;                /* string table position of name */
    int type;                   /* symbol type - see flags below */
    long value;                 /* address, or COMMON variable size */
    long size;                  /* size for data or function exports */
    long segment;               /* back-reference used by gsym_reloc */
    struct Symbol *next;        /* list of globals in each section */
    struct Symbol *nextfwd;     /* list of unresolved-size symbols */
    char *name;                 /* for unresolved-size symbols */
    long symnum;                /* index into symbol table */
};

/*
 * Section IDs - used in Reloc.symbol when negative, and in
 * Symbol.type when positive.
 */
#define SECT_ABS 2              /* absolute value */
#define SECT_TEXT 4             /* text section */
#define SECT_DATA 6             /* data section */
#define SECT_BSS 8              /* bss section */
#define SECT_MASK 0xE           /* mask out any of the above */

/*
 * More flags used in Symbol.type.
 */
#define SYM_GLOBAL 1            /* it's a global symbol */
#define SYM_DATA 0x100          /* used for shared libs */
#define SYM_FUNCTION 0x200      /* used for shared libs */
#define SYM_WITH_SIZE 0x4000    /* not output; internal only */

/*
 * Bit more explanation of symbol types: SECT_xxx denotes a local
 * symbol. SECT_xxx|SYM_GLOBAL denotes a global symbol, defined in
 * this module. Just SYM_GLOBAL, with zero value, denotes an
 * external symbol referenced in this module. And just SYM_GLOBAL,
 * but with a non-zero value, declares a C `common' variable, of
 * size `value'.
 */

struct Section {
    struct SAA *data;
    unsigned long len, size, nrelocs;
    long index;
    struct Reloc *head, **tail;
    struct Symbol *gsyms, *asym;
};

static struct Section stext, sdata, sbss;

static struct SAA *syms;
static unsigned long nsyms;

static struct RAA *bsym;

static struct SAA *strs;
static unsigned long strslen;

static struct Symbol *fwds;

static FILE *aoutfp;
static efunc error;
static evalfunc evaluate;

static int bsd;
static int is_pic;

static void aout_write(void);
static void aout_write_relocs(struct Reloc *);
static void aout_write_syms(void);
static void aout_sect_write(struct Section *, const unsigned char *,
                            unsigned long);
static void aout_pad_sections(void);
static void aout_fixup_relocs(struct Section *);

/*
 * Special section numbers which are used to define special
 * symbols, which can be used with WRT to provide PIC relocation
 * types.
 */
static long aout_gotpc_sect, aout_gotoff_sect;
static long aout_got_sect, aout_plt_sect;
static long aout_sym_sect;

static void aoutg_init(FILE * fp, efunc errfunc, ldfunc ldef,
                       evalfunc eval)
{
    aoutfp = fp;
    error = errfunc;
    evaluate = eval;
    (void)ldef;                 /* placate optimisers */
    stext.data = saa_init(1L);
    stext.head = NULL;
    stext.tail = &stext.head;
    sdata.data = saa_init(1L);
    sdata.head = NULL;
    sdata.tail = &sdata.head;
    stext.len = stext.size = sdata.len = sdata.size = sbss.len = 0;
    stext.nrelocs = sdata.nrelocs = 0;
    stext.gsyms = sdata.gsyms = sbss.gsyms = NULL;
    stext.index = seg_alloc();
    sdata.index = seg_alloc();
    sbss.index = seg_alloc();
    stext.asym = sdata.asym = sbss.asym = NULL;
    syms = saa_init((long)sizeof(struct Symbol));
    nsyms = 0;
    bsym = raa_init();
    strs = saa_init(1L);
    strslen = 0;
    fwds = NULL;
}

#ifdef OF_AOUT

static void aout_init(FILE * fp, efunc errfunc, ldfunc ldef, evalfunc eval)
{
    bsd = FALSE;
    aoutg_init(fp, errfunc, ldef, eval);

    aout_gotpc_sect = aout_gotoff_sect = aout_got_sect =
        aout_plt_sect = aout_sym_sect = NO_SEG;
}

#endif

#ifdef OF_AOUTB

extern struct ofmt of_aoutb;

static void aoutb_init(FILE * fp, efunc errfunc, ldfunc ldef,
                       evalfunc eval)
{
    bsd = TRUE;
    aoutg_init(fp, errfunc, ldef, eval);

    is_pic = 0x00;              /* may become 0x40 */

    aout_gotpc_sect = seg_alloc();
    ldef("..gotpc", aout_gotpc_sect + 1, 0L, NULL, FALSE, FALSE, &of_aoutb,
         error);
    aout_gotoff_sect = seg_alloc();
    ldef("..gotoff", aout_gotoff_sect + 1, 0L, NULL, FALSE, FALSE,
         &of_aoutb, error);
    aout_got_sect = seg_alloc();
    ldef("..got", aout_got_sect + 1, 0L, NULL, FALSE, FALSE, &of_aoutb,
         error);
    aout_plt_sect = seg_alloc();
    ldef("..plt", aout_plt_sect + 1, 0L, NULL, FALSE, FALSE, &of_aoutb,
         error);
    aout_sym_sect = seg_alloc();
    ldef("..sym", aout_sym_sect + 1, 0L, NULL, FALSE, FALSE, &of_aoutb,
         error);
}

#endif

static void aout_cleanup(int debuginfo)
{
    struct Reloc *r;

    (void)debuginfo;

    aout_pad_sections();
    aout_fixup_relocs(&stext);
    aout_fixup_relocs(&sdata);
    aout_write();
    fclose(aoutfp);
    saa_free(stext.data);
    while (stext.head) {
        r = stext.head;
        stext.head = stext.head->next;
        nasm_free(r);
    }
    saa_free(sdata.data);
    while (sdata.head) {
        r = sdata.head;
        sdata.head = sdata.head->next;
        nasm_free(r);
    }
    saa_free(syms);
    raa_free(bsym);
    saa_free(strs);
}

static long aout_section_names(char *name, int pass, int *bits)
{
    /*
     * Default to 32 bits.
     */
    if (!name)
        *bits = 32;

    if (!name)
        return stext.index;

    if (!strcmp(name, ".text"))
        return stext.index;
    else if (!strcmp(name, ".data"))
        return sdata.index;
    else if (!strcmp(name, ".bss"))
        return sbss.index;
    else
        return NO_SEG;
}

static void aout_deflabel(char *name, long segment, long offset,
                          int is_global, char *special)
{
    int pos = strslen + 4;
    struct Symbol *sym;
    int special_used = FALSE;

    if (name[0] == '.' && name[1] == '.' && name[2] != '@') {
        /*
         * This is a NASM special symbol. We never allow it into
         * the a.out 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->segment = segment;
    if (segment == NO_SEG)
        sym->type |= SECT_ABS;
    else if (segment == stext.index) {
        sym->type |= SECT_TEXT;
        if (is_global) {
            sym->next = stext.gsyms;
            stext.gsyms = sym;
        } else if (!stext.asym)
            stext.asym = sym;
    } else if (segment == sdata.index) {
        sym->type |= SECT_DATA;
        if (is_global) {
            sym->next = sdata.gsyms;
            sdata.gsyms = sym;
        } else if (!sdata.asym)
            sdata.asym = sym;
    } else if (segment == sbss.index) {
        sym->type |= SECT_BSS;
        if (is_global) {
            sym->next = sbss.gsyms;
            sbss.gsyms = sym;
        } else if (!sbss.asym)
            sbss.asym = sym;
    } else
        sym->type = SYM_GLOBAL;
    if (is_global == 2)
        sym->value = offset;
    else
        sym->value = (sym->type == SYM_GLOBAL ? 0 : offset);

    if (is_global && sym->type != SYM_GLOBAL) {
        /*
         * Global symbol exported _from_ this module. We must check
         * the special text for type information.
         */

        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 */

                if (!bsd) {
                    error(ERR_NONFATAL, "Linux a.out does not support"
                          " symbol size information");
                } else {
                    while (special[n] && isspace(special[n]))
                        n++;
                    /*
                     * We have a size expression; attempt to
                     * evaluate it.
                     */
                    sym->type |= SYM_WITH_SIZE;
                    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;
        }
    }

    /*
     * define the references from external-symbol segment numbers
     * to these symbol records.
     */
    if (segment != NO_SEG && segment != stext.index &&
        segment != sdata.index && segment != sbss.index)
        bsym = raa_write(bsym, segment, nsyms);
    sym->symnum = nsyms;

    nsyms++;
    if (sym->type & SYM_WITH_SIZE)
        nsyms++;                /* and another for the size */

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

static void aout_add_reloc(struct Section *sect, long segment,
                           int reltype, int bytes)
{
    struct Reloc *r;

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

    r->address = sect->len;
    r->symbol = (segment == NO_SEG ? -SECT_ABS :
                 segment == stext.index ? -SECT_TEXT :
                 segment == sdata.index ? -SECT_DATA :
                 segment == sbss.index ? -SECT_BSS :
                 raa_read(bsym, segment));
    r->reltype = reltype;
    if (r->symbol >= 0)
        r->reltype |= RELTYPE_SYMFLAG;
    r->bytes = bytes;

    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.
 *
 * RELTYPE_GOT references require the _exact_ symbol address to be
 * used; RELTYPE_ABSOLUTE 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 aout_add_gsym_reloc(struct Section *sect,
                                long segment, long offset,
                                int type, int bytes, int exact)
{
    struct Symbol *sym, *sm, *shead;
    struct Reloc *r;

    /*
     * First look up the segment to find whether it's text, data,
     * bss or an external symbol.
     */
    shead = NULL;
    if (segment == stext.index)
        shead = stext.gsyms;
    else if (segment == sdata.index)
        shead = sdata.gsyms;
    else if (segment == sbss.index)
        shead = sbss.gsyms;
    if (!shead) {
        if (exact && offset != 0)
            error(ERR_NONFATAL, "unable to find a suitable global symbol"
                  " for this reference");