ldrdf.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

/*
 * ldrdf.c - RDOFF Object File linker/loader main program.
 *
 * Copyright (c) 1996,99 Julian Hall. All rights reserved.
 * Improvements and fixes (c) 1999-2004 RET & COM Research.
 *
 * This file is distributed under the terms and conditions of the
 * GNU Lesser Public License (LGPL), version 2.1.
 * See http://www.gnu.org/copyleft/lgpl.html for details.
 */

/*
 * TODO:
 * - enhance search of required export symbols in libraries (now depends
 *   on modules order in library)
 * - keep a cache of symbol names in each library module so
 *   we don't have to constantly recheck the file
 * - general performance improvements
 *
 * BUGS & LIMITATIONS: this program doesn't support multiple code, data
 * or bss segments, therefore for 16 bit programs whose code, data or BSS
 * segment exceeds 64K in size, it will not work. This program probably
 * won't work if compiled by a 16 bit compiler. Try DJGPP if you're running
 * under DOS. '#define STINGY_MEMORY' may help a little.
 */

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

#define RDOFF_UTILS

#include "rdoff.h"
#include "symtab.h"
#include "collectn.h"
#include "rdlib.h"
#include "segtab.h"

#define LDRDF_VERSION "1.07"

/* #define STINGY_MEMORY */

/* =======================================================================
 * Types & macros that are private to this program
 */

struct segment_infonode {
    int dest_seg;               /* output segment to be placed into, -1 to 
                                   skip linking this segment */
    long reloc;                 /* segment's relocation factor */
};

struct modulenode {
    rdffile f;                  /* the RDOFF file structure */
    struct segment_infonode seginfo[RDF_MAXSEGS];       /* what are we doing
                                                           with each segment? */
    void *header;
    char *name;
    struct modulenode *next;
    long bss_reloc;
};

#include "ldsegs.h"

#define newstr(str) strcpy(malloc(strlen(str) + 1),str)
#define newstrcat(s1,s2) strcat(strcpy(malloc(strlen(s1)+strlen(s2)+1),s1),s2)

/* ==========================================================================
 * Function prototypes of private utility functions
 */

void processmodule(const char *filename, struct modulenode *mod);
int allocnewseg(uint16 type, uint16 reserved);
int findsegment(uint16 type, uint16 reserved);
void symtab_add(const char *symbol, int segment, long offset);
int symtab_get(const char *symbol, int *segment, long *offset);

/* =========================================================================
 * Global data structures.
 */

/* a linked list of modules that will be included in the output */
struct modulenode *modules = NULL;
struct modulenode *lastmodule = NULL;

/* a linked list of libraries to be searched for unresolved imported symbols */
struct librarynode *libraries = NULL;
struct librarynode *lastlib = NULL;

/* the symbol table */
void *symtab = NULL;

/* objects search path */
char *objpath = NULL;

/* libraries search path */
char *libpath = NULL;

/* file to embed as a generic record */
char *generic_rec_file = NULL;

/* error file */
static FILE *error_file;

/* the header of the output file, built up stage by stage */
rdf_headerbuf *newheader = NULL;

/* The current state of segment allocation, including information about
 * which output segment numbers have been allocated, and their types and
 * amount of data which has already been allocated inside them. 
 */
struct SegmentHeaderRec outputseg[RDF_MAXSEGS];
int nsegs = 0;
long bss_length;

/* global options which affect how the program behaves */
struct ldrdfoptions {
    int verbose;
    int align;
    int dynalink;
    int strip;
    int respfile;
    int stderr_redir;
    int objpath;
    int libpath;
} options;

int errorcount = 0;             /* determines main program exit status */

/* =========================================================================
 * Utility functions
 */

/*
 * initsegments()
 *
 * sets up segments 0, 1, and 2, the initial code data and bss segments
 */
void initsegments()
{
    nsegs = 3;
    outputseg[0].type = 1;
    outputseg[0].number = 0;
    outputseg[0].reserved = 0;
    outputseg[0].length = 0;
    outputseg[1].type = 2;
    outputseg[1].number = 1;
    outputseg[1].reserved = 0;
    outputseg[1].length = 0;
    outputseg[2].type = 0xFFFF; /* reserved segment type */
    outputseg[2].number = 2;
    outputseg[2].reserved = 0;
    outputseg[2].length = 0;
    bss_length = 0;
}

/*
 * loadmodule
 *
 * Determine the characteristics of a module, and decide what to do with
 * each segment it contains (including determining destination segments and
 * relocation factors for segments that	are kept).
 */
void loadmodule(const char *filename)
{
    if (options.verbose)
        printf("loading `%s'\n", filename);

    /* allocate a new module entry on the end of the modules list */
    if (!modules) {
        modules = malloc(sizeof(*modules));
        lastmodule = modules;
    } else {
        lastmodule->next = malloc(sizeof(*modules));
        lastmodule = lastmodule->next;
    }

    if (!lastmodule) {
        fprintf(stderr, "ldrdf: out of memory\n");
        exit(1);
    }

    /* open the file using 'rdfopen', which returns nonzero on error */
    if (rdfopen(&lastmodule->f, filename) != 0) {
        rdfperror("ldrdf", filename);
        exit(1);
    }

    /* 
     * store information about the module, and determine what segments
     * it contains, and what we should do with them (determine relocation
     * factor if we decide to keep them)
     */
    lastmodule->header = NULL;
    lastmodule->name = strdup(filename);
    lastmodule->next = NULL;

    processmodule(filename, lastmodule);
}

/*
 * processmodule()
 *
 * step through each segment, determine what exactly we're doing with
 * it, and if we intend to keep it, determine (a) which segment to
 * put it in and (b) whereabouts in that segment it will end up.
 * (b) is fairly easy, because we're now keeping track of how big each
 * segment in our output file is...
 */
void processmodule(const char *filename, struct modulenode *mod)
{
    struct segconfig sconf;
    int seg, outseg;
    void *header;
    rdfheaderrec *hr;
    long bssamount = 0;
    int bss_was_referenced = 0;

    for (seg = 0; seg < mod->f.nsegs; seg++) {
        /*
         * get the segment configuration for this type from the segment
         * table. getsegconfig() is a macro, defined in ldsegs.h.
         */
        getsegconfig(sconf, mod->f.seg[seg].type);

        if (options.verbose > 1) {
            printf("%s %04x [%04x:%10s] ", filename,
                   mod->f.seg[seg].number, mod->f.seg[seg].type,
                   sconf.typedesc);
        }
        /*
         * sconf->dowhat tells us what to do with a segment of this type.
         */
        switch (sconf.dowhat) {
        case SEG_IGNORE:
            /*
             * Set destination segment to -1, to indicate that this segment
             * should be ignored for the purpose of output, ie it is left
             * out of the linked executable.
             */
            mod->seginfo[seg].dest_seg = -1;
            if (options.verbose > 1)
                printf("IGNORED\n");
            break;

        case SEG_NEWSEG:
            /*
             * The configuration tells us to create a new segment for
             * each occurrence of this segment type.
             */
            outseg = allocnewseg(sconf.mergetype,
                                 mod->f.seg[seg].reserved);
            mod->seginfo[seg].dest_seg = outseg;
            mod->seginfo[seg].reloc = 0;
            outputseg[outseg].length = mod->f.seg[seg].length;
            if (options.verbose > 1)
                printf("=> %04x:%08lx (+%04lx)\n", outseg,
                       mod->seginfo[seg].reloc, mod->f.seg[seg].length);
            break;

        case SEG_MERGE:
            /*
             * The configuration tells us to merge the segment with
             * a previously existing segment of type 'sconf.mergetype',
             * if one exists. Otherwise a new segment is created.
             * This is handled transparently by 'findsegment()'.
             */
            outseg = findsegment(sconf.mergetype,
                                 mod->f.seg[seg].reserved);
            mod->seginfo[seg].dest_seg = outseg;

            /*
             * We need to add alignment to these segments.
             */
            if (outputseg[outseg].length % options.align != 0)
                outputseg[outseg].length +=
                    options.align -
                    (outputseg[outseg].length % options.align);

            mod->seginfo[seg].reloc = outputseg[outseg].length;
            outputseg[outseg].length += mod->f.seg[seg].length;

            if (options.verbose > 1)
                printf("=> %04x:%08lx (+%04lx)\n", outseg,
                       mod->seginfo[seg].reloc, mod->f.seg[seg].length);
        }

    }

    /*
     * extract symbols from the header, and dump them into the
     * symbol table
     */
    header = malloc(mod->f.header_len);
    if (!header) {
        fprintf(stderr, "ldrdf: not enough memory\n");
        exit(1);
    }
    if (rdfloadseg(&mod->f, RDOFF_HEADER, header)) {
        rdfperror("ldrdf", filename);
        exit(1);
    }

    while ((hr = rdfgetheaderrec(&mod->f))) {
        switch (hr->type) {
        case RDFREC_IMPORT:    /* imported symbol */
        case RDFREC_FARIMPORT:
            /* Define with seg = -1 */
            symtab_add(hr->i.label, -1, 0);
            break;

        case RDFREC_GLOBAL:{   /* exported symbol */
                int destseg;
                long destreloc;

                if (hr->e.segment == 2) {
                    bss_was_referenced = 1;
                    destreloc = bss_length;
                    if (destreloc % options.align != 0)
                        destreloc +=
                            options.align - (destreloc % options.align);
                    destseg = 2;
                } else {
                    if ((destseg =
                         mod->seginfo[(int)hr->e.segment].dest_seg) == -1)
                        continue;
                    destreloc = mod->seginfo[(int)hr->e.segment].reloc;
                }
                symtab_add(hr->e.label, destseg, destreloc + hr->e.offset);
                break;
            }

        case RDFREC_BSS:       /* BSS reservation */
            /*
             * first, amalgamate all BSS reservations in this module
             * into one, because we allow this in the output format.
             */
            bssamount += hr->b.amount;
            break;

        case RDFREC_COMMON:{   /* Common variable */
                symtabEnt *ste = symtabFind(symtab, hr->c.label);

                /* Is the symbol already in the table? */
                if (ste)
                    break;

                /* Align the variable */
                if (bss_length % hr->c.align != 0)
                    bss_length += hr->c.align - (bss_length % hr->c.align);
                if (options.verbose > 1) {
                    printf("%s %04x common '%s' => 0002:%08lx (+%04lx)\n",
                           filename, hr->c.segment, hr->c.label,
                           bss_length, hr->c.size);
                }

                symtab_add(hr->c.label, 2, bss_length);
                mod->bss_reloc = bss_length;
                bss_length += hr->c.size;
                break;
            }
        }
    }

    if (bssamount != 0 || bss_was_referenced) {
        /*
         * handle the BSS segment - first pad the existing bss length
         * to the correct alignment, then store the length in bss_reloc
         * for this module. Then add this module's BSS length onto
         * bss_length.
         */
        if (bss_length % options.align != 0)
            bss_length += options.align - (bss_length % options.align);

        mod->bss_reloc = bss_length;
        if (options.verbose > 1) {
            printf("%s 0002 [            BSS] => 0002:%08lx (+%04lx)\n",
                   filename, bss_length, bssamount);
        }
        bss_length += bssamount;
    }
#ifdef STINGY_MEMORY
    /*
     * we free the header buffer here, to save memory later.
     * this isn't efficient, but probably halves the memory usage
     * of this program...
     */
    mod->f.header_loc = NULL;
    free(header);

#endif

}

/*
 * Return 1 if a given module is in the list, 0 otherwise.
 */
int lookformodule(const char *name)
{
    struct modulenode *curr = modules;

    while (curr) {
        if (!strcmp(name, curr->name))
            return 1;
        curr = curr->next;
    }
    return 0;
}

/*
 * allocnewseg()
 * findsegment()
 *
 * These functions manipulate the array of output segments, and are used
 * by processmodule(). allocnewseg() allocates a segment in the array,
 * initialising it to be empty. findsegment() first scans the array for
 * a segment of the type requested, and if one isn't found allocates a
 * new one.
 */
int allocnewseg(uint16 type, uint16 reserved)
{
    outputseg[nsegs].type = type;
    outputseg[nsegs].number = nsegs;
    outputseg[nsegs].reserved = reserved;
    outputseg[nsegs].length = 0;
    outputseg[nsegs].offset = 0;
    outputseg[nsegs].data = NULL;

    return nsegs++;
}

int findsegment(uint16 type, uint16 reserved)
{
    int i;

    for (i = 0; i < nsegs; i++)
        if (outputseg[i].type == type)
            return i;

    return allocnewseg(type, reserved);
}

/*