rdfload.c

一个汇编语言编译器源码

/* rdfload.c	RDOFF Object File loader library
 *
 * 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.
 *
 * Permission to use this file in your own projects is granted, as long
 * as acknowledgement is given in an appropriate manner to its authors,
 * with instructions of how to obtain a copy via ftp.
 */

/*
 * TODO: this has been modified from previous version only in very
 * simplistic ways. Needs to be improved drastically, especially:
 *   - support for more than the 2 standard segments
 *   - support for segment relocations (hard to do in ANSI C)
 */

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

#include "rdfload.h"
#include "symtab.h"
#include "rdoff.h"
#include "collectn.h"

extern int rdf_errno;

rdfmodule * rdfload(const char *filename)
{
    rdfmodule 	* f = malloc(sizeof(rdfmodule));
    long 	bsslength = 0;
    char	* hdr;
    rdfheaderrec *r;

    if (f == NULL) 
    {
	rdf_errno = 6;		/* out of memory */
	return NULL;
    }

    f->symtab = symtabNew();
    if (!f->symtab)
    {
	free(f);
	rdf_errno = 6;
	return NULL;
    }

    /* open the file */
    if ( rdfopen( &(f->f), filename ) ) {
	free(f);
	return NULL;
    }

    /* read in text and data segments, and header */
    
    f->t = malloc (f->f.seg[0].length);
    f->d = malloc (f->f.seg[1].length); /* BSS seg allocated later */
    hdr = malloc (f->f.header_len);

    if (! f->t || ! f->d || !hdr) {
	rdf_errno = 6;
	rdfclose(&f->f);
	if (f->t) free(f->t);
	if (f->d) free(f->d);
	free(f);
	return NULL;
    }

    if ( rdfloadseg (&f->f,RDOFF_HEADER,hdr) ||
	 rdfloadseg (&f->f,RDOFF_CODE,f->t) ||
	 rdfloadseg (&f->f,RDOFF_DATA,f->d) )
    {
	rdfclose(&f->f);
	free(f->t);
	free(f->d);
	free(f);
	free(hdr);
	return NULL;
    }

    rdfclose(&f->f);

    /* Allocate BSS segment; step through header and count BSS records */

    while ( ( r = rdfgetheaderrec (&f->f) ) )
    {
	if (r->type == 5)
	    bsslength += r->b.amount;
    }

    f->b = malloc ( bsslength );
    if (! f->b )
    {
	free(f->t);
	free(f->d);
	free(f);
	free(hdr);
	rdf_errno = 6;
	return NULL;
    }

    rdfheaderrewind (&f->f);

    f->textrel = (long)f->t;
    f->datarel = (long)f->d;
    f->bssrel  = (long)f->b;

    return f;
}

int rdf_relocate(rdfmodule * m)
{
    rdfheaderrec	* r;
    Collection		imports;    
    symtabEnt		e;
    long		rel;
    unsigned char	* seg;
    
    rdfheaderrewind ( & m->f );
    collection_init(&imports);

    while ( (r = rdfgetheaderrec ( & m->f ) ) )
    {
	switch (r->type)
	{
	case 1:		/* Relocation record */

	    /* calculate relocation factor */

	    if (r->r.refseg == 0) rel = m->textrel;
	    else if (r->r.refseg == 1) rel = m->datarel;
	    else if (r->r.refseg == 2) rel = m->bssrel;
	    else
		/* We currently do not support load-time linkage.
		   This should be added some time soon... */

		return 1;	/* return error code */

	    if ((r->r.segment & 63) == 0) seg = m->t;
	    else if ((r->r.segment & 63) == 1) seg = m->d;
	    else
		continue;	/* relocation not in a loaded segment */

	    /* it doesn't matter in this case that the code is non-portable,
	       as the entire concept of executing a module like this is
	       non-portable */
	    switch(r->r.length) {
	    case 1:
		seg[r->r.offset] += (char) rel;
		break;
	    case 2:
		*(int16 *)(seg + r->r.offset) += (int16) rel;
		break;
	    case 4:
		*(long *)(seg + r->r.offset) += rel;
		break;
	    }
	    break;

	case 3:			/* export record - add to symtab */
	    e.segment = r->e.segment;
	    e.offset = r->e.offset + 
	               (e.segment == 0 ? m->textrel : /* 0 -> code */
			e.segment == 1 ? m->datarel : /* 1 -> data */
			                 m->bssrel) ; /* 2 -> bss  */
	    e.flags = 0;
	    e.name = malloc(strlen(r->e.label) + 1);
	    if (! e.name)
		return 1;

	    strcpy(e.name,r->e.label);
	    symtabInsert(m->symtab,&e);
	    break;

	case 6:			/* segment relocation */
	    fprintf(stderr, "%s: segment relocation not supported by this "
		    "loader\n", m->f.name);
	    return 1;
	}
    }    
    return 0;
}