ld/ld.1

   1 .\" Copyright (c) 1991, 1992 Free Software Foundation
   2 .\" See section COPYING for conditions for redistribution
   3 .TH ld 1 "17 August 1992" "cygnus support" "GNU Development Tools"
   4 .de BP
   5 .sp
   6 .ti \-.2i
   7 \(**
   8 ..
   9
  10 .SH NAME
  11 ld \- the GNU linker
  12
  13 .SH SYNOPSIS
  14 .hy 0
  15 .na
  16 .TP
  17 .B ld
  18 .RB "[\|" \-o "
  19 .I output\c
  20 \&\|] \c
  21 .I objfile\c
  22 \&.\|.\|.
  23 .br
  24 .RB "[\|" \-A\c
  25 .I architecture\c
  26 \&\|]
  27 .RB "[\|" "\-b\ "\c
  28 .I input-format\c
  29 \&\|]
  30 .RB "[\|" \-Bstatic "\|]"
  31 .RB "[\|" "\-c\ "\c
  32 .I commandfile\c
  33 \&\|]
  34 .RB "[\|" \-d | \-dc | \-dp\c
  35 \|]
  36 .br
  37 .RB "[\|" "\-defsym\ "\c
  38 .I symbol\c
  39 \& = \c
  40 .I expression\c
  41 \&\|]
  42 .RB "[\|" "\-e\ "\c
  43 .I entry\c
  44 \&\|]
  45 .RB "[\|" \-F "\|]"
  46 .RB "[\|" "\-F\ "\c
  47 .I format\c
  48 \&\|]
  49 .RB "[\|" "\-format\ "\c
  50 .I input-format\c
  51 \&\|]
  52 .RB "[\|" \-g "\|]"
  53 .RB "[\|" \-G\c
  54 .I size\c
  55 \&\|]
  56 .RB "[\|" \-i "\|]"
  57 .RB "[\|" \-l\c
  58 .I ar\c
  59 \&\|]
  60 .RB "[\|" \-L\c
  61 .I searchdir\c
  62 \&\|]
  63 .RB "[\|" \-M "\|]"
  64 .RB "[\|" \-m\c
  65 .I emulation\c
  66 \&\|]
  67 .RB "[\|" \-n | \-N "\|]"
  68 .RB "[\|" \-noinhibit-exec "\|]"
  69 .RB "[\|" "\-R\ "\c
  70 .I filename\c
  71 \&\|]
  72 .RB "[\|" \-relax "\|]"
  73 .RB "[\|" \-r | \-Ur "\|]"
  74 .RB "[\|" \-S "\|]"
  75 .RB "[\|" \-s "\|]"
  76 .RB "[\|" "\-T\ "\c
  77 .I commandfile\c
  78 \&\|]
  79 .RB "[\|" "\-Ttext\ "\c
  80 .I textorg\c
  81 \&\|]
  82 .RB "[\|" "\-Tdata\ "\c
  83 .I dataorg\c
  84 \&\|]
  85 .RB "[\|" "\-Tbss\ "\c
  86 .I bssorg\c
  87 \&\|]
  88 .RB "[\|" \-t "\|]"
  89 .RB "[\|" "\-u\ "\c
  90 .I sym\c
  91 \&]
  92 .RB "[\|" \-V "\|]"
  93 .RB "[\|" \-v "\|]"
  94 .RB "[\|" \-X "\|]"
  95 .RB "[\|" \-x "\|]"
  96 .RB "[\|" { \c
  97 .I script\c
  98 .BR } "\|]"
  99 .ad b
 100 .hy 1
 101 .SH DESCRIPTION
 102 \c
 103 .B ld\c
 104 \& combines a number of object and archive files, relocates
 105 their data and ties up symbol references. Often the last step in
 106 building a new compiled program to run is a call to \c
 107 .B ld\c
 108 \&.
 109
 110 \c
 111 .B ld\c
 112 \& accepts Linker Command Language files
 113 to provide explicit and total control over the linking process.
 114 This man page does not describe the command language; see the `\|\c
 115 .B ld\c
 116 \|' entry in `\|\c
 117 .B info\c
 118 \|', or the manual
 119 .I
 120 ld: the GNU linker
 121 \&, for full details on the command language and on other aspects of
 122 the GNU linker.
 123
 124 This version of \c
 125 .B ld\c
 126 \& uses the general purpose BFD libraries
 127 to operate on object files. This allows \c
 128 .B ld\c
 129 \& to read, combine, and
 130 write object files in many different formats\(em\&for example, COFF or
 131 \c
 132 .B a.out\c
 133 \&.  Different formats may be linked together to produce any
 134 available kind of object file.  You can use `\|\c
 135 .B objdump \-i\c
 136 \|' to get a list of formats supported on various architectures; see
 137 .BR objdump ( 1 ).
 138
 139 Aside from its flexibility, the GNU linker is more helpful than other
 140 linkers in providing diagnostic information.  Many linkers abandon
 141 execution immediately upon encountering an error; whenever possible,
 142 \c
 143 .B ld\c
 144 \& continues executing, allowing you to identify other errors
 145 (or, in some cases, to get an output file in spite of the error).
 146
 147 The GNU linker \c
 148 .B ld\c
 149 \& is meant to cover a broad range of situations,
 150 and to be as compatible as possible with other linkers.  As a result,
 151 you have many choices to control its behavior through the command line,
 152 and through environment variables.
 153
 154 .SH OPTIONS
 155 The plethora of command-line options may seem intimidating, but in
 156 actual practice few of them are used in any particular context.
 157 For instance, a frequent use of \c
 158 .B ld\c
 159 \& is to link standard Unix
 160 object files on a standard, supported Unix system.  On such a system, to
 161 link a file \c
 162 .B hello.o\c
 163 \&:
 164 .sp
 165 .br
 166 $\ ld\ \-o\ output\ /lib/crt0.o\ hello.o\ \-lc
 167 .br
 168 .sp
 169 This tells \c
 170 .B ld\c
 171 \& to produce a file called \c
 172 .B output\c
 173 \& as the
 174 result of linking the file \c
 175 .B /lib/crt0.o\c
 176 \& with \c
 177 .B hello.o\c
 178 \& and
 179 the library \c
 180 .B libc.a\c
 181 \& which will come from the standard search
 182 directories.
 183
 184 The command-line options to \c
 185 .B ld\c
 186 \& may be specified in any order, and
 187 may be repeated at will.  For the most part, repeating an option with a
 188 different argument will either have no further effect, or override prior
 189 occurrences (those further to the left on the command line) of an
 190 option.
 191
 192 The exceptions\(em\&which may meaningfully be used more than once\(em\&are
 193 \c
 194 .B \-A\c
 195 \&, \c
 196 .B \-b\c
 197 \& (or its synonym \c
 198 .B \-format\c
 199 \&), \c
 200 .B \-defsym\c
 201 \&,
 202 \c
 203 .B \-L\c
 204 \&, \c
 205 .B \-l\c
 206 \&, \c
 207 .B \-R\c
 208 \&, and \c
 209 .B \-u\c
 210 \&.
 211
 212 The list of object files to be linked together, shown as \c
 213 .I objfile\c
 214 \&,
 215 may follow, precede, or be mixed in with command-line options; save that
 216 an \c
 217 .I objfile\c
 218 \& argument may not be placed between an option flag and
 219 its argument.
 220
 221 Usually the linker is invoked with at least one object file, but other
 222 forms of binary input files can also be specified with \c
 223 .B \-l\c
 224 \&,
 225 \c
 226 .B \-R\c
 227 \&, and the script command language.  If \c
 228 .I no\c
 229 \& binary input
 230 files at all are specified, the linker does not produce any output, and
 231 issues the message `\|\c
 232 .B No input files\c
 233 \|'.
 234
 235 Option arguments must either follow the option letter without intervening
 236 whitespace, or be given as separate arguments immediately following the
 237 option that requires them.
 238
 239 .TP
 240 .BI "-A" "architecture"\c
 241 \&
 242 In the current release of \c
 243 .B ld\c
 244 \&, this option is useful only for the
 245 Intel 960 family of architectures.  In that \c
 246 .B ld\c
 247 \& configuration, the
 248 \c
 249 .I architecture\c
 250 \& argument is one of the two-letter names identifying
 251 members of the 960 family; the option specifies the desired output
 252 target, and warns of any incompatible instructions in the input files.
 253 It also modifies the linker's search strategy for archive libraries, to
 254 support the use of libraries specific to each particular
 255 architecture, by including in the search loop names suffixed with the
 256 string identifying the architecture.
 257
 258 For example, if your \c
 259 .B ld\c
 260 \& command line included `\|\c
 261 .B \-ACA\c
 262 \|' as
 263 well as `\|\c
 264 .B \-ltry\c
 265 \|', the linker would look (in its built-in search
 266 paths, and in any paths you specify with \c
 267 .B \-L\c
 268 \&) for a library with
 269 the names
 270 .sp
 271 .br
 272 try
 273 .br
 274 libtry.a
 275 .br
 276 tryca
 277 .br
 278 libtryca.a
 279 .br
 280 .sp
 281
 282 The first two possibilities would be considered in any event; the last
 283 two are due to the use of `\|\c
 284 .B \-ACA\c
 285 \|'.
 286
 287 Future releases of \c
 288 .B ld\c
 289 \& may support similar functionality for
 290 other architecture families.
 291
 292 You can meaningfully use \c
 293 .B \-A\c
 294 \& more than once on a command line, if
 295 an architecture family allows combination of target architectures; each
 296 use will add another pair of name variants to search for when \c
 297 .B \-l\c
 298 \&
 299 specifies a library.
 300
 301 .TP
 302 .BI "-b " "input-format"\c
 303 \&
 304 Specify the binary format for input object files that follow this option
 305 on the command line.  You don't usually need to specify this, as
 306 \c
 307 .B ld\c
 308 \& is configured to expect as a default input format the most
 309 usual format on each machine.  \c
 310 .I input-format\c
 311 \& is a text string, the
 312 name of a particular format supported by the BFD libraries.
 313 \c
 314 .B \-format \c
 315 .I input-format\c
 316 \&\c
 317 \& has the same effect.
 318
 319 You may want to use this option if you are linking files with an unusual
 320 binary format.  You can also use \c
 321 .B \-b\c
 322 \& to switch formats explicitly (when
 323 linking object files of different formats), by including
 324 \c
 325 .B \-b \c
 326 .I input-format\c
 327 \&\c
 328 \& before each group of object files in a
 329 particular format.
 330
 331 The default format is taken from the environment variable
 332 .B GNUTARGET\c
 333 \&.  You can also define the input
 334 format from a script, using the command \c
 335 .B TARGET\c
 336 \&.
 337
 338 .TP
 339 .B \-Bstatic
 340 This flag is accepted for command-line compatibility with the SunOS linker,
 341 but has no effect on \c
 342 .B ld\c
 343 \&.
 344
 345 .TP
 346 .BI "-c " "commandfile"\c
 347 \&
 348 Directs \c
 349 .B ld\c
 350 \& to read link commands from the file
 351 \c
 352 .I commandfile\c
 353 \&.  These commands will completely override \c
 354 .B ld\c
 355 \&'s
 356 default link format (rather than adding to it); \c
 357 .I commandfile\c
 358 \& must
 359 specify everything necessary to describe the target format.
 360
 361
 362 You may also include a script of link commands directly in the command
 363 line by bracketing it between `\|\c
 364 .B {\c
 365 \|' and `\|\c
 366 .B }\c
 367 \|' characters.
 368
 369 .TP
 370 .B \-d
 371 .TP
 372 .B \-dc
 373 .TP
 374 .B \-dp
 375 These three options are equivalent; multiple forms are supported for
 376 compatibility with other linkers.  Use any of them to make \c
 377 .B ld\c
 378 \&
 379 assign space to common symbols even if a relocatable output file is
 380 specified (\c
 381 .B \-r\c
 382 \&).  The script command
 383 \c
 384 .B FORCE_COMMON_ALLOCATION\c
 385 \& has the same effect.
 386
 387 .TP
 388 .BI "-defsym " "symbol"\c
 389 \& = \c
 390 .I expression\c
 391 \&
 392 Create a global symbol in the output file, containing the absolute
 393 address given by \c
 394 .I expression\c
 395 \&.  You may use this option as many
 396 times as necessary to define multiple symbols in the command line.  A
 397 limited form of arithmetic is supported for the \c
 398 .I expression\c
 399 \& in this
 400 context: you may give a hexadecimal constant or the name of an existing
 401 symbol, or use \c
 402 .B +\c
 403 \& and \c
 404 .B \-\c
 405 \& to add or subtract hexadecimal
 406 constants or symbols.  If you need more elaborate expressions, consider
 407 using the linker command language from a script.
 408
 409 .TP
 410 .BI "-e " "entry"\c
 411 \&
 412 Use \c
 413 .I entry\c
 414 \& as the explicit symbol for beginning execution of your
 415 program, rather than the default entry point.  for a
 416 discussion of defaults and other ways of specifying the
 417 entry point.
 418
 419 .TP
 420 .B \-F
 421 .TP
 422 .BI "-F" "format"\c
 423 \&
 424 Some older linkers used this option throughout a compilation toolchain
 425 for specifying object-file format for both input and output object
 426 files.  \c
 427 .B ld\c
 428 \&'s mechanisms (the \c
 429 .B \-b\c
 430 \& or \c
 431 .B \-format\c
 432 \& options
 433 for input files, the \c
 434 .B TARGET\c
 435 \& command in linker scripts for output
 436 files, the \c
 437 .B GNUTARGET\c
 438 \& environment variable) are more flexible, but
 439 but it accepts (and ignores) the \c
 440 .B \-F\c
 441 \& option flag for compatibility
 442 with scripts written to call the old linker.
 443
 444 .TP
 445 .BI "-format " "input-format"\c
 446 \&
 447 Synonym for \c
 448 .B \-b\c
 449 \& \c
 450 .I input-format\c
 451 \&.
 452
 453 .TP
 454 .B \-g
 455 Accepted, but ignored; provided for compatibility with other tools.
 456
 457 .TP
 458 .BI "\-G " "size"\c
 459 Set the maximum size of objects to be optimized using the GP register
 460 to
 461 .I size
 462 under MIPS ECOFF.  Ignored for other object file formats.
 463
 464 .TP
 465 .B \-i
 466 Perform an incremental link (same as option \c
 467 .B \-r\c
 468 \&).
 469
 470 .TP
 471 .BI "-l" "ar"\c
 472 \&
 473 Add an archive file \c
 474 .I ar\c
 475 \& to the list of files to link.  This
 476 option may be used any number of times.  \c
 477 .B ld\c
 478 \& will search its
 479 path-list for occurrences of \c
 480 .B lib\c
 481 .I ar\c
 482 \&.a\c
 483 \& for every \c
 484 .I ar\c
 485 \&
 486 specified.
 487
 488 .TP
 489 .BI "-L" "searchdir"\c
 490 \&
 491 This command adds path \c
 492 .I searchdir\c
 493 \& to the list of paths that
 494 \c
 495 .B ld\c
 496 \& will search for archive libraries.  You may use this option
 497 any number of times.
 498
 499 The default set of paths searched (without being specified with
 500 \c
 501 .B \-L\c
 502 \&) depends on what emulation mode \c
 503 .B ld\c
 504 \& is using, and in
 505 some cases also on how it was configured.    The
 506 paths can also be specified in a link script with the \c
 507 .B SEARCH_DIR\c
 508 \&
 509 command.
 510
 511 .TP
 512 .B \-M
 513 Print (to the standard output file) a link map\(em\&diagnostic information
 514 about where symbols are mapped by \c
 515 .B ld\c
 516 \&, and information on global
 517 common storage allocation.
 518
 519 .TP
 520 .BI "\-m " "emulation"\c
 521 Emulate the
 522 .I emulation
 523 linker.  You can list the available emulations with the
 524 .I \-V
 525 option.  This option overrides the compiled-in default, which is the
 526 system for which you configured
 527 .BR ld .
 528
 529 .TP
 530 .B \-N
 531 specifies readable and writable \c
 532 .B text\c
 533 \& and \c
 534 .B data\c
 535 \& sections. If
 536 the output format supports Unix style magic numbers, the output is
 537 marked as \c
 538 .B OMAGIC\c
 539 \&.
 540
 541 When you use the `\|\c
 542 .B \-N\c
 543 \&\|' option, the linker does not page-align the
 544 data segment.
 545
 546 .TP
 547 .B \-n
 548 sets the text segment to be read only, and \c
 549 .B NMAGIC\c
 550 \& is written
 551 if possible.
 552
 553 .TP
 554 .B \-noinhibit-exec
 555 Normally, the linker will not produce an output file if it encounters
 556 errors during the link process.  With this flag, you can specify that
 557 you wish the output file retained even after non-fatal errors.
 558
 559 .TP
 560 .BI "-o " "output"\c
 561 \&
 562 .I output\c
 563 \&
 564 \c
 565 .I output\c
 566 \& is a name for the program produced by \c
 567 .B ld\c
 568 \&; if this
 569 option is not specified, the name `\|\c
 570 .B a.out\c
 571 \|' is used by default.  The
 572 script command \c
 573 .B OUTPUT\c
 574 \& can also specify the output file name.
 575
 576 .TP
 577 .BI "-R " "filename"\c
 578 \&
 579 .I file\c
 580 \&
 581 Read symbol names and their addresses from \c
 582 .I filename\c
 583 \&, but do not
 584 relocate it or include it in the output.  This allows your output file
 585 to refer symbolically to absolute locations of memory defined in other
 586 programs.
 587
 588 .TP
 589 .B \-relax
 590 An option with machine dependent effects.  Currently this option is only
 591 supported on the H8/300.
 592
 593 On some platforms, use this option to perform global optimizations that
 594 become possible when the linker resolves addressing in your program, such
 595 as relaxing address modes and synthesizing new instructions in the
 596 output object file.
 597
 598 On platforms where this is not supported, `\|\c
 599 .B \-relax\c
 600 \&\|' is accepted, but has no effect.
 601
 602 .TP
 603 .B \-r
 604 Generates relocatable output\(em\&i.e., generate an output file that can in
 605 turn serve as input to \c
 606 .B ld\c
 607 \&.  This is often called \c
 608 .I partial
 609 linking\c
 610 \&.  As a side effect, in environments that support standard Unix
 611 magic numbers, this option also sets the output file's magic number to
 612 \c
 613 .B OMAGIC\c
 614 \&.
 615 If this option is not specified, an absolute file is produced.  When
 616 linking C++ programs, this option \c
 617 .I will not\c
 618 \& resolve references to
 619 constructors; \c
 620 .B \-Ur\c
 621 \& is an alternative.
 622
 623 This option does the same as \c
 624 .B \-i\c
 625 \&.
 626
 627 .TP
 628 .B \-S
 629 Omits debugger symbol information (but not all symbols) from the output file.
 630
 631 .TP
 632 .B \-s
 633 Omits all symbol information from the output file.
 634
 635 .TP
 636 .BI "{ " "script" " }"
 637 You can, if you wish, include a script of linker commands directly in
 638 the command line instead of referring to it via an input file.  When the
 639 character `\|\c
 640 .B {\c
 641 \|' occurs on the command line, the linker switches to
 642 interpreting the command language until the end of the list of commands
 643 is reached\(em\&flagged with a closing brace `\|\c
 644 .B }\c
 645 \|'.  Other command-line
 646 options will not be recognized while parsing the script.
 647 See the `\|\c
 648 .B ld\c
 649 \|' entry in `\|\c
 650 .B info\c
 651 \|', or the manual
 652 .I
 653 ld: the GNU linker
 654 \&, for a description of the command language.
 655
 656 .TP
 657 .BI "-Tbss " "org"\c
 658 .TP
 659 .BI "-Tdata " "org"\c
 660 .TP
 661 .BI "-Ttext " "org"\c
 662 Use \c
 663 .I org\c
 664 \& as the starting address for\(em\&respectively\(em\&the
 665 \c
 666 .B bss\c
 667 \&, \c
 668 .B data\c
 669 \&, or the \c
 670 .B text\c
 671 \& segment of the output file.
 672 \c
 673 .I textorg\c
 674 \& must be a hexadecimal integer.
 675
 676 .TP
 677 .BI "-T " "commandfile"\c
 678 \&
 679 .TP
 680 .BI "-T" "commandfile"\c
 681 Equivalent to \c
 682 .B \-c \c
 683 .I commandfile\c
 684 \&\c
 685 \&; supported for compatibility with
 686 other tools.
 687
 688 .TP
 689 .B \-t
 690 Prints names of input files as \c
 691 .B ld\c
 692 \& processes them.
 693
 694 .TP
 695 .BI "-u " "sym"
 696 Forces \c
 697 .I sym\c
 698 \& to be entered in the output file as an undefined symbol.
 699 This may, for example, trigger linking of additional modules from
 700 standard libraries.  \c
 701 .B \-u\c
 702 \& may be repeated with different option
 703 arguments to enter additional undefined symbols.
 704
 705 .TP
 706 .B \-Ur
 707 For anything other than C++ programs, this option is equivalent to
 708 \c
 709 .B \-r\c
 710 \&: it generates relocatable output\(em\&i.e., an output file that can in
 711 turn serve as input to \c
 712 .B ld\c
 713 \&.  When linking C++ programs, \c
 714 .B \-Ur\c
 715 \&
 716 \c
 717 .I will\c
 718 \& resolve references to constructors, unlike \c
 719 .B \-r\c
 720 \&.
 721
 722 .TP
 723 .B \-V
 724 Display the version number for \c
 725 .B ld
 726 and list the supported emulations.
 727 Print which input files can and can not be opened.
 728
 729 .TP
 730 .B \-v
 731 Display the version number for \c
 732 .B ld\c
 733 \&.
 734 Print which input files can and can not be opened.
 735
 736 .TP
 737 .B \-X
 738 If \c
 739 .B \-s\c
 740 \& or \c
 741 .B \-S\c
 742 \& is also specified, delete only local symbols
 743 beginning with `\|\c
 744 .B L\c
 745 \|'.
 746
 747 .TP
 748 .B \-x
 749 If \c
 750 .B \-s\c
 751 \& or \c
 752 .B \-S\c
 753 \& is also specified, delete all local symbols,
 754 not just those beginning with `\|\c
 755 .B L\c
 756 \|'.
 757
 758 .PP
 759
 760 .SH ENVIRONMENT
 761 \c
 762 You can change the behavior of
 763 .B ld\c
 764 \& with the environment variable \c
 765 .B GNUTARGET\c
 766 \&.
 767
 768 \c
 769 .B GNUTARGET\c
 770 \& determines the input-file object format if you don't
 771 use \c
 772 .B \-b\c
 773 \& (or its synonym \c
 774 .B \-format\c
 775 \&).  Its value should be one
 776 of the BFD names for an input format.  If there is no
 777 \c
 778 .B GNUTARGET\c
 779 \& in the environment, \c
 780 .B ld\c
 781 \& uses the natural format
 782 of the host. If \c
 783 .B GNUTARGET\c
 784 \& is set to \c
 785 .B default\c
 786 \& then BFD attempts to discover the
 787 input format by examining binary input files; this method often
 788 succeeds, but there are potential ambiguities, since there is no method
 789 of ensuring that the magic number used to flag object-file formats is
 790 unique.  However, the configuration procedure for BFD on each system
 791 places the conventional format for that system first in the search-list,
 792 so ambiguities are resolved in favor of convention.
 793
 794 .PP
 795
 796 .SH "SEE ALSO"
 797
 798 .BR objdump ( 1 )
 799 .br
 800 .br
 801 .RB "`\|" ld "\|' and `\|" binutils "\|'"
 802 entries in
 803 .B info\c
 804 .br
 805 .I
 806 ld: the GNU linker\c
 807 , Steve Chamberlain and Roland Pesch;
 808 .I
 809 The GNU Binary Utilities\c
 810 , Roland H. Pesch.
 811
 812 .SH COPYING
 813 Copyright (c) 1991, 1992 Free Software Foundation, Inc.
 814 .PP
 815 Permission is granted to make and distribute verbatim copies of
 816 this manual provided the copyright notice and this permission notice
 817 are preserved on all copies.
 818 .PP
 819 Permission is granted to copy and distribute modified versions of this
 820 manual under the conditions for verbatim copying, provided that the
 821 entire resulting derived work is distributed under the terms of a
 822 permission notice identical to this one.
 823 .PP
 824 Permission is granted to copy and distribute translations of this
 825 manual into another language, under the above conditions for modified
 826 versions, except that this permission notice may be included in
 827 translations approved by the Free Software Foundation instead of in
 828 the original English.