outaout.c

一个免费的汇编语言编译器的源代码

    if (exact) {
	/*
	 * Find a symbol pointing _exactly_ at this one.
	 */
	for (sym = shead; sym; sym = sym->next)
	    if (sym->value == offset)
		break;
    } else {
	/*
	 * Find the nearest symbol below this one.
	 */
	sym = NULL;
	for (sm = shead; 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 = sym->symnum;
    r->reltype = type | RELTYPE_SYMFLAG;
    r->bytes = bytes;

    sect->nrelocs++;

    return offset - sym->value;
}

/*
 * This routine deals with ..gotoff relocations. These _must_ refer
 * to a symbol, due to a perversity of *BSD's PIC implementation,
 * and it must be a non-global one as well; so we store `asym', the
 * first nonglobal symbol defined in each section, and always work
 * from that. Relocation type is always RELTYPE_GOTOFF.
 *
 * Return value is the adjusted value of `addr', having become an
 * offset from the `asym' symbol rather than the section.
 */
static long aout_add_gotoff_reloc (struct Section *sect, long segment,
				   long offset, int bytes) 
{
    struct Reloc *r;
    struct Symbol *asym;

    /*
     * First look up the segment to find whether it's text, data,
     * bss or an external symbol.
     */
    asym = NULL;
    if (segment == stext.index)
	asym = stext.asym;
    else if (segment == sdata.index)
	asym = sdata.asym;
    else if (segment == sbss.index)
	asym = sbss.asym;
    if (!asym)
	error (ERR_NONFATAL, "`..gotoff' relocations require a non-global"
	       " symbol in the section");

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

    r->address = sect->len;
    r->symbol = asym->symnum;
    r->reltype = RELTYPE_GOTOFF;
    r->bytes = bytes;

    sect->nrelocs++;

    return offset - asym->value;
}

static void aout_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;

    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;
    }

    if (segto == stext.index)
	s = &stext;
    else if (segto == sdata.index)
	s = &sdata;
    else if (segto == sbss.index)
	s = NULL;
    else {
	error(ERR_WARNING, "attempt to assemble code in"
	      " segment %d: defaulting to `.text'", segto);
	s = &stext;
    }

    if (!s && type != OUT_RESERVE) {
	error(ERR_WARNING, "attempt to initialise memory in the"
	      " BSS section: ignored");
	if (type == OUT_REL2ADR)
	    realbytes = 2;
	else if (type == OUT_REL4ADR)
	    realbytes = 4;
	sbss.len += realbytes;
	return;
    }

    if (type == OUT_RESERVE) {
	if (s) {
	    error(ERR_WARNING, "uninitialised space declared in"
		  " %s section: zeroing",
		  (segto == stext.index ? "code" : "data"));
	    aout_sect_write (s, NULL, realbytes);
	} else
	    sbss.len += realbytes;
    } else if (type == OUT_RAWDATA) {
	if (segment != NO_SEG)
	    error(ERR_PANIC, "OUT_RAWDATA with other than NO_SEG");
	aout_sect_write (s, data, realbytes);
    } else if (type == OUT_ADDRESS) {
	addr = *(long *)data;
	if (segment != NO_SEG) {
	    if (segment % 2) {
		error(ERR_NONFATAL, "a.out format does not support"
		      " segment base references");
	    } else {
		if (wrt == NO_SEG) {
		    aout_add_reloc (s, segment, RELTYPE_ABSOLUTE, realbytes);
		} else if (!bsd) {
		    error (ERR_NONFATAL, "Linux a.out format does not support"
			   " any use of WRT");
		    wrt = NO_SEG;      /* we can at least _try_ to continue */
		} else if (wrt == aout_gotpc_sect+1) {
		    is_pic = 0x40;
		    aout_add_reloc (s, segment, RELTYPE_GOTPC, realbytes);
		} else if (wrt == aout_gotoff_sect+1) {
		    is_pic = 0x40;
		    addr = aout_add_gotoff_reloc (s, segment,
						  addr, realbytes);
		} else if (wrt == aout_got_sect+1) {
		    is_pic = 0x40;
		    addr = aout_add_gsym_reloc (s, segment, addr, RELTYPE_GOT,
						realbytes, TRUE);
		} else if (wrt == aout_sym_sect+1) {
		    addr = aout_add_gsym_reloc (s, segment, addr,
						RELTYPE_ABSOLUTE, realbytes,
						FALSE);
		} else if (wrt == aout_plt_sect+1) {
		    is_pic = 0x40;
		    error(ERR_NONFATAL, "a.out format cannot produce non-PC-"
			  "relative PLT references");
		} else {
		    error (ERR_NONFATAL, "a.out format does not support this"
			   " use of WRT");
		    wrt = NO_SEG;      /* we can at least _try_ to continue */
		}
	    }
	}
	p = mydata;
	if (realbytes == 2)
	    WRITESHORT (p, addr);
	else
	    WRITELONG (p, addr);
	aout_sect_write (s, mydata, realbytes);
    } else if (type == OUT_REL2ADR) {
	if (segment == segto)
	    error(ERR_PANIC, "intra-segment OUT_REL2ADR");
	if (segment != NO_SEG && segment % 2) {
	    error(ERR_NONFATAL, "a.out format does not support"
		  " segment base references");
	} else {
	    if (wrt == NO_SEG) {
		aout_add_reloc (s, segment, RELTYPE_RELATIVE, 2);
	    } else if (!bsd) {
		error (ERR_NONFATAL, "Linux a.out format does not support"
		       " any use of WRT");
		wrt = NO_SEG;      /* we can at least _try_ to continue */
	    } else if (wrt == aout_plt_sect+1) {
		is_pic = 0x40;
		aout_add_reloc (s, segment, RELTYPE_PLT, 2);
	    } else if (wrt == aout_gotpc_sect+1 ||
		       wrt == aout_gotoff_sect+1 ||
		       wrt == aout_got_sect+1) {
		error(ERR_NONFATAL, "a.out format cannot produce PC-"
		      "relative GOT references");
	    } else {
		error (ERR_NONFATAL, "a.out format does not support this"
		       " use of WRT");
		wrt = NO_SEG;      /* we can at least _try_ to continue */
	    }
	}
	p = mydata;
	WRITESHORT (p, *(long*)data-(realbytes + s->len));
	aout_sect_write (s, mydata, 2L);
    } else if (type == OUT_REL4ADR) {
	if (segment == segto)
	    error(ERR_PANIC, "intra-segment OUT_REL4ADR");
	if (segment != NO_SEG && segment % 2) {
	    error(ERR_NONFATAL, "a.out format does not support"
		  " segment base references");
	} else {
	    if (wrt == NO_SEG) {
		aout_add_reloc (s, segment, RELTYPE_RELATIVE, 4);
	    } else if (!bsd) {
		error (ERR_NONFATAL, "Linux a.out format does not support"
		       " any use of WRT");
		wrt = NO_SEG;      /* we can at least _try_ to continue */
	    } else if (wrt == aout_plt_sect+1) {
		is_pic = 0x40;
		aout_add_reloc (s, segment, RELTYPE_PLT, 4);
	    } else if (wrt == aout_gotpc_sect+1 ||
		       wrt == aout_gotoff_sect+1 ||
		       wrt == aout_got_sect+1) {
		error(ERR_NONFATAL, "a.out format cannot produce PC-"
		      "relative GOT references");
	    } else {
		error (ERR_NONFATAL, "a.out format does not support this"
		       " use of WRT");
		wrt = NO_SEG;      /* we can at least _try_ to continue */
	    }
	}
	p = mydata;
	WRITELONG (p, *(long*)data-(realbytes + s->len));
	aout_sect_write (s, mydata, 4L);
    }
}

static void aout_pad_sections(void) 
{
    static unsigned char pad[] = { 0x90, 0x90, 0x90, 0x90 };
    /*
     * Pad each of the text and data sections with NOPs until their
     * length is a multiple of four. (NOP == 0x90.) Also increase
     * the length of the BSS section similarly.
     */
    aout_sect_write (&stext, pad, (-(long)stext.len) & 3);
    aout_sect_write (&sdata, pad, (-(long)sdata.len) & 3);
    sbss.len = (sbss.len + 3) & ~3;
}

/*
 * a.out files have the curious property that all references to
 * things in the data or bss sections are done by addresses which
 * are actually relative to the start of the _text_ section, in the
 * _file_. (No relation to what happens after linking. No idea why
 * this should be so. It's very strange.) So we have to go through
 * the relocation table, _after_ the final size of each section is
 * known, and fix up the relocations pointed to.
 */
static void aout_fixup_relocs(struct Section *sect) 
{
    struct Reloc *r;

    saa_rewind (sect->data);
    for (r = sect->head; r; r = r->next) {
	unsigned char *p, *q, blk[4];
	long l;

	saa_fread (sect->data, r->address, blk, (long)r->bytes);
	p = q = blk;
	l = *p++;
	if (r->bytes > 1) {
	    l += ((long)*p++) << 8;
	    if (r->bytes == 4) {
		l += ((long)*p++) << 16;
		l += ((long)*p++) << 24;
	    }
	}
	if (r->symbol == -SECT_DATA)
	    l += stext.len;
	else if (r->symbol == -SECT_BSS)
	    l += stext.len + sdata.len;
	if (r->bytes == 4)
	    WRITELONG(q, l);
	else if (r->bytes == 2)
	    WRITESHORT(q, l);
	else
	    *q++ = l & 0xFF;
	saa_fwrite (sect->data, r->address, blk, (long)r->bytes);
    }
}

static void aout_write(void) 
{
    /*
     * Emit the a.out header.
     */
    /* OMAGIC, M_386 or MID_I386, no flags */
    fwritelong (bsd ? 0x07018600 | is_pic : 0x640107L, aoutfp);
    fwritelong (stext.len, aoutfp);
    fwritelong (sdata.len, aoutfp);
    fwritelong (sbss.len, aoutfp);
    fwritelong (nsyms * 12, aoutfp);   /* length of symbol table */
    fwritelong (0L, aoutfp);	       /* object files have no entry point */
    fwritelong (stext.nrelocs * 8, aoutfp);   /* size of text relocs */
    fwritelong (sdata.nrelocs * 8, aoutfp);   /* size of data relocs */

    /*
     * Write out the code section and the data section.
     */
    saa_fpwrite (stext.data, aoutfp);
    saa_fpwrite (sdata.data, aoutfp);

    /*
     * Write out the relocations.
     */
    aout_write_relocs (stext.head);
    aout_write_relocs (sdata.head);

    /*
     * Write the symbol table.
     */
    aout_write_syms ();

    /*
     * And the string table.
     */
    fwritelong (strslen+4, aoutfp);    /* length includes length count */
    saa_fpwrite (strs, aoutfp);
}

static void aout_write_relocs (struct Reloc *r) 
{
    while (r) {
	unsigned long word2;

	fwritelong (r->address, aoutfp);

	if (r->symbol >= 0)
	    word2 = r->symbol;
	else
	    word2 = -r->symbol;
	word2 |= r->reltype << 24;
	word2 |= (r->bytes == 1 ? 0 :
		  r->bytes == 2 ? 0x2000000L : 0x4000000L);
	fwritelong (word2, aoutfp);

	r = r->next;
    }
}

static void aout_write_syms (void) 
{
    unsigned long i;

    saa_rewind (syms);
    for (i = 0; i < nsyms; i++) {
	struct Symbol *sym = saa_rstruct(syms);
	fwritelong (sym->strpos, aoutfp);
	fwritelong ((long)sym->type & ~SYM_WITH_SIZE, aoutfp);
	/*
	 * Fix up the symbol value now we know the final section
	 * sizes.
	 */
	if ((sym->type & SECT_MASK) == SECT_DATA)
	    sym->value += stext.len;
	if ((sym->type & SECT_MASK) == SECT_BSS)
	    sym->value += stext.len + sdata.len;
	fwritelong (sym->value, aoutfp);
	/*
	 * Output a size record if necessary.
	 */
	if (sym->type & SYM_WITH_SIZE) {
	    fwritelong(sym->strpos, aoutfp);
	    fwritelong(0x0DL, aoutfp);  /* special value: means size */
	    fwritelong(sym->size, aoutfp);
	    i++;		       /* use up another of `nsyms' */
	}
    }
}

static void aout_sect_write (struct Section *sect,
			     const unsigned char *data, unsigned long len) 
{
    saa_wbytes (sect->data, data, len);
    sect->len += len;
}

static long aout_segbase (long segment) 
{
    return segment;
}

static int aout_directive (char *directive, char *value, int pass) 
{
    return 0;
}

static void aout_filename (char *inname, char *outname, efunc error) 
{
    standard_extension (inname, outname, ".o", error);
}

static const char *aout_stdmac[] = {
    "%define __SECT__ [section .text]",
    "%macro __NASM_CDecl__ 1",
    "%endmacro",
    NULL
};

static int aout_set_info(enum geninfo type, char **val)
{
    return 0;
}
#endif /* OF_AOUT || OF_AOUTB */

#ifdef OF_AOUT

struct ofmt of_aout = {
    "Linux a.out object files",
    "aout",
    NULL,
    null_debug_arr,
    &null_debug_form,
    aout_stdmac,
    aout_init,
    aout_set_info,
    aout_out,
    aout_deflabel,
    aout_section_names,
    aout_segbase,
    aout_directive,
    aout_filename,
    aout_cleanup
};

#endif

#ifdef OF_AOUTB

struct ofmt of_aoutb = {
    "NetBSD/FreeBSD a.out object files",
    "aoutb",
    NULL,
    null_debug_arr,
    &null_debug_form,
    aout_stdmac,
    aoutb_init,
    aout_set_info,
    aout_out,
    aout_deflabel,
    aout_section_names,
    aout_segbase,
    aout_directive,
    aout_filename,
    aout_cleanup
};

#endif