ghc/docs/users_guide/phases.sgml

   1   <sect1 id="options-phases">
   2     <title>Options related to a particular phase</title>
   3
   4     <sect2 id="replacing-phases">
   5       <title>Replacing the program for one or more phases</title>
   6       <indexterm><primary>phases, changing</primary></indexterm>
   7
   8       <para>You may specify that a different program be used for one
   9       of the phases of the compilation system, in place of whatever
  10       the <Command>ghc</Command> has wired into it.  For example, you
  11       might want to try a different assembler.  The following options
  12       allow you to change the external program used for a given
  13       compilation phase:</para>
  14
  15       <variablelist>
  16         <varlistentry>
  17           <term><option>-pgmL</option> <replaceable>cmd</replaceable></term>
  18           <indexterm><primary><option>-pgmL</option></primary>
  19           </indexterm>
  20           <listitem>
  21             <para>Use <replaceable>cmd</replaceable> as the literate
  22             pre-processor.</para>
  23           </listitem>
  24         </varlistentry>
  25
  26         <varlistentry>
  27           <term><option>-pgmP</option> <replaceable>cmd</replaceable></term>
  28           <indexterm><primary><option>-pgmP</option></primary>
  29           </indexterm>
  30           <listitem>
  31             <para>Use <replaceable>cmd</replaceable> as the C
  32             pre-processor (with <option>-cpp</option> only).</para>
  33           </listitem>
  34         </varlistentry>
  35
  36         <varlistentry>
  37           <term><option>-pgmc</option> <replaceable>cmd</replaceable></term>
  38           <indexterm><primary><option>-pgmc</option></primary>
  39           </indexterm>
  40           <listitem>
  41             <para>Use <replaceable>cmd</replaceable> as the C
  42             compiler.</para>
  43           </listitem>
  44         </varlistentry>
  45
  46         <varlistentry>
  47           <term><option>-pgma</option> <replaceable>cmd</replaceable></term>
  48           <indexterm><primary><option>-pgma</option></primary>
  49           </indexterm>
  50           <listitem>
  51             <para>Use <replaceable>cmd</replaceable> as the
  52             assembler.</para>
  53           </listitem>
  54         </varlistentry>
  55
  56         <varlistentry>
  57           <term><option>-pgml</option> <replaceable>cmd</replaceable></term>
  58           <indexterm><primary><option>-pgml</option></primary>
  59           </indexterm>
  60           <listitem>
  61             <para>Use <replaceable>cmd</replaceable> as the
  62             linker.</para>
  63           </listitem>
  64         </varlistentry>
  65
  66         <varlistentry>
  67           <term><option>-pgmdll</option> <replaceable>cmd</replaceable></term>
  68           <indexterm><primary><option>-pgmdll</option></primary>
  69           </indexterm>
  70           <listitem>
  71             <para>Use <replaceable>cmd</replaceable> as the DLL
  72             generator.</para>
  73           </listitem>
  74         </varlistentry>
  75
  76         <varlistentry>
  77           <term><option>-pgmdep</option> <replaceable>cmd</replaceable></term>
  78           <indexterm><primary><option>-pgmdep</option></primary>
  79           </indexterm>
  80           <listitem>
  81             <para>Use <replaceable>cmd</replaceable> as the dependency
  82             generator.</para>
  83           </listitem>
  84         </varlistentry>
  85
  86         <varlistentry>
  87           <term><option>-pgmF</option> <replaceable>cmd</replaceable></term>
  88           <indexterm><primary><option>-pgmF</option></primary>
  89           </indexterm>
  90           <listitem>
  91             <para>Use <replaceable>cmd</replaceable> as the
  92             pre-processor (with <option>-F</option> only).</para>
  93           </listitem>
  94         </varlistentry>
  95       </variablelist>
  96
  97     </sect2>
  98
  99     <sect2 id="forcing-options-through">
 100       <title>Forcing options to a particular phase</title>
 101       <indexterm><primary>forcing GHC-phase options</primary></indexterm>
 102
 103       <para>Options can be forced through to a particlar compilation
 104       phase, using the following flags:</para>
 105
 106
 107       <para>So, for example, to force an <option>-Ewurble</option>
 108       option to the assembler, you would tell the driver
 109       <option>-opta-Ewurble</option> (the dash before the E is
 110       required).</para>
 111
 112       <para>GHC is itself a Haskell program, so if you need to pass
 113       options directly to GHC's runtime system you can enclose them in
 114       <literal>+RTS ... -RTS</literal> (see <xref
 115       linkend="runtime-control">).</para>
 116
 117     </sect2>
 118
 119     <sect2 id="c-pre-processor">
 120       <title>Options affecting the C pre-processor</title>
 121
 122       <indexterm><primary>pre-processing: cpp</primary></indexterm>
 123       <indexterm><primary>C pre-processor options</primary></indexterm>
 124       <indexterm><primary>cpp, pre-processing with</primary></indexterm>
 125
 126       <variablelist>
 127
 128         <varlistentry>
 129           <term><option>-cpp</option></term>
 130           <indexterm><primary><option>-cpp</option></primary></indexterm>
 131           <listitem>
 132             <para>The C pre-processor <command>cpp</command> is run
 133             over your Haskell code only if the <option>-cpp</option>
 134             option <indexterm><primary>-cpp
 135             option</primary></indexterm> is given.  Unless you are
 136             building a large system with significant doses of
 137             conditional compilation, you really shouldn't need
 138             it.</para>
 139           </listitem>
 140         </varlistentry>
 141
 142         <varlistentry>
 143           <term><option>-D</option><replaceable>symbol</replaceable><optional>=<replaceable>value</replaceable></optional></term>
 144           <indexterm><primary><option>-D</option></primary></indexterm>
 145           <listitem>
 146             <para>Define macro <replaceable>symbol</replaceable> in the
 147             usual way.  NB: does <emphasis>not</emphasis> affect
 148             <option>-D</option> macros passed to the C&nbsp;compiler
 149             when compiling via C!  For those, use the
 150             <option>-optc-Dfoo</option> hack&hellip; (see <xref
 151             linkend="forcing-options-through">).</para>
 152           </listitem>
 153         </varlistentry>
 154
 155         <varlistentry>
 156           <term><option>-U</option><replaceable>symbol</replaceable></term>
 157           <indexterm><primary><option>-U</option></primary></indexterm>
 158           <listitem>
 159             <para> Undefine macro <replaceable>symbol</replaceable> in the
 160             usual way.</para>
 161           </listitem>
 162         </varlistentry>
 163
 164         <varlistentry>
 165           <term><option>-I</option><replaceable>dir</replaceable></term>
 166           <indexterm><primary><option>-I</option></primary></indexterm>
 167           <listitem>
 168             <para> Specify a directory in which to look for
 169             <literal>&num;include</literal> files, in the usual C
 170             way.</para>
 171           </listitem>
 172         </varlistentry>
 173       </variablelist>
 174
 175       <para>The GHC driver pre-defines several macros when processing
 176       Haskell source code (<filename>.hs</filename> or
 177       <filename>.lhs</filename> files):</para>
 178
 179       <variablelist>
 180
 181         <varlistentry>
 182           <term><constant>&lowbar;&lowbar;HASKELL98&lowbar;&lowbar;</constant></term>
 183           <indexterm><primary><literal>&lowbar;&lowbar;HASKELL98&lowbar;&lowbar;</literal></primary></indexterm>
 184           <listitem>
 185             <para>If defined, this means that GHC supports the
 186             language defined by the Haskell 98 report.</para>
 187           </listitem>
 188         </varlistentry>
 189
 190         <varlistentry>
 191           <term><constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;=98</constant></term>
 192           <indexterm><primary><constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;=98</constant></primary></indexterm>
 193           <listitem>
 194             <para>In GHC 4.04 and later, the
 195             <constant>&lowbar;&lowbar;HASKELL&lowbar;&lowbar;</constant>
 196             macro is defined as having the value
 197             <constant>98</constant>.</para>
 198           </listitem>
 199         </varlistentry>
 200
 201         <varlistentry>
 202           <term><constant>&lowbar;&lowbar;HASKELL1&lowbar;&lowbar;</constant></term>
 203           <indexterm><primary><constant>&lowbar;&lowbar;HASKELL1&lowbar;&lowbar;
 204           </constant></primary></indexterm>
 205           <listitem>
 206             <para>If defined to <replaceable>n</replaceable>, that
 207             means GHC supports the Haskell language defined in the
 208             Haskell report version <emphasis>1.n</emphasis>.
 209             Currently 5.  This macro is deprecated, and will probably
 210             disappear in future versions.</para>
 211           </listitem>
 212         </varlistentry>
 213
 214         <varlistentry>
 215           <term><constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 216           <indexterm><primary><constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 217           <listitem>
 218             <para>For version <replaceable>n</replaceable> of the GHC
 219             system, this will be <literal>&num;define</literal>d to
 220             <replaceable>100n</replaceable>.  For example, for version
 221             5.00, it is 500.</para>
 222
 223             <para>With any luck,
 224             <constant>&lowbar;&lowbar;GLASGOW&lowbar;HASKELL&lowbar;&lowbar;</constant>
 225             will be undefined in all other implementations that
 226             support C-style pre-processing.</para>
 227
 228             <para>(For reference: the comparable symbols for other
 229             systems are:
 230             <constant>&lowbar;&lowbar;HUGS&lowbar;&lowbar;</constant>
 231             for Hugs,
 232             <constant>&lowbar;&lowbar;NHC&lowbar;&lowbar;</constant>
 233             for nhc98, and
 234             <constant>&lowbar;&lowbar;HBC&lowbar;&lowbar;</constant>
 235             for Chalmers.)</para>
 236
 237             <para>NB. This macro is set when pre-processing both
 238             Haskell source and C source, including the C source
 239             generated from a Haskell module
 240             (i.e. <filename>.hs</filename>, <filename>.lhs</filename>,
 241             <filename>.c</filename> and <filename>.hc</filename>
 242             files).</para>
 243           </listitem>
 244         </varlistentry>
 245
 246         <varlistentry>
 247           <term><constant>&lowbar;&lowbar;CONCURRENT&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 248           <indexterm><primary><constant>&lowbar;&lowbar;CONCURRENT&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 249           <listitem>
 250             <para>This symbol is defined when pre-processing Haskell
 251             (input) and pre-processing C (GHC output).  Since GHC from
 252             verion 4.00 now supports concurrent haskell by default,
 253             this symbol is always defined.</para>
 254           </listitem>
 255         </varlistentry>
 256
 257         <varlistentry>
 258           <term><constant>&lowbar;&lowbar;PARALLEL&lowbar;HASKELL&lowbar;&lowbar;</constant></term>
 259           <indexterm><primary><constant>&lowbar;&lowbar;PARALLEL&lowbar;HASKELL&lowbar;&lowbar;</constant></primary></indexterm>
 260           <listitem>
 261             <para>Only defined when <option>-parallel</option> is in
 262             use!  This symbol is defined when pre-processing Haskell
 263             (input) and pre-processing C (GHC output).</para>
 264           </listitem>
 265         </varlistentry>
 266       </variablelist>
 267
 268       <para>A small word of warning: <option>-cpp</option> is not
 269       friendly to &ldquo;string gaps&rdquo;.<indexterm><primary>-cpp
 270       vs string gaps</primary></indexterm><indexterm><primary>string
 271       gaps vs -cpp</primary></indexterm>.  In other words, strings
 272       such as the following:</para>
 273
 274 <ProgramListing>
 275 strmod = "\
 276 \ p \
 277 \ "
 278 </ProgramListing>
 279
 280       <para>don't work with <option>-cpp</option>;
 281       <filename>/usr/bin/cpp</filename> elides the backslash-newline
 282       pairs.</para>
 283
 284       <para>However, it appears that if you add a space at the end of
 285       the line, then <command>cpp</command> (at least GNU
 286       <command>cpp</command> and possibly other
 287       <command>cpp</command>s) leaves the backslash-space pairs alone
 288       and the string gap works as expected.</para>
 289     </sect2>
 290
 291     <sect2 id="pre-processor">
 292       <title>Options affecting a Haskell pre-processor</title>
 293
 294       <indexterm><primary>pre-processing: custom</primary></indexterm>
 295       <indexterm><primary>Pre-processor options</primary></indexterm>
 296
 297       <variablelist>
 298         <varlistentry>
 299           <term><option>-F</option></term>
 300           <indexterm><primary><option>-F</option></primary></indexterm>
 301           <listitem>
 302             <para>A custom pre-processor is run over your Haskell
 303             source file only if the <option>-F</option> option
 304             <indexterm><primary>-F</primary></indexterm> is given.
 305             </para>
 306             <para>
 307             Running a custom pre-processor at compile-time is in some
 308             settings appropriate and useful. The <option>-F</option>
 309             option lets you run a pre-processor as part of the overall
 310             GHC compilation pipeline, which has the advantage over
 311             running a Haskell pre-processor separately in that it
 312             works in interpreted mode and you can continue to take
 313             reap the benefits of GHC's recompilation checker.
 314             </para>
 315             <para>
 316             The pre-processor is run just before the Haskell
 317             compiler proper processes the Haskell input, but after
 318             the literate markup has been stripped away and (possibly)
 319             the C pre-processor has washed the Haskell input.
 320             </para>
 321           </listitem>
 322         </varlistentry>
 323         <varlistentry>
 324           <term><option>-pgmF</option> <replaceable>cmd</replaceable></term>
 325           <indexterm><primary><option>-pgmF</option> <replaceable>cmd</replaceable></primary></indexterm>
 326           <listitem>
 327             <para>Use <replaceable>cmd</replaceable> as the Haskell
 328           pre-processor. When invoked, the
 329           <replaceable>cmd</replaceable> pre-processor is given at
 330           least three arguments on its command-line: the first
 331           argument is the name of the original source file, the second
 332           is the name of the file holding the input, and the third is
 333           the name of the file where
 334           <replaceable>cmd</replaceable> should write its output to.
 335           </para>
 336           <para>Additional arguments to the
 337           <replaceable>cmd</replaceable> pre-processor can be passed
 338           in using the <option>-optF</option> option. These are fed to
 339           <replaceable>cmd</replaceable> on the command line after the
 340           three standard input and output arguments.
 341         </para>
 342           </listitem>
 343         </varlistentry>
 344       </variablelist>
 345     </sect2>
 346
 347     <sect2 id="options-C-compiler">
 348       <title>Options affecting the C compiler (if applicable)</title>
 349
 350       <indexterm><primary>include-file options</primary></indexterm>
 351       <indexterm><primary>C compiler options</primary></indexterm>
 352       <indexterm><primary>GCC options</primary></indexterm>
 353
 354       <para>If you are compiling with lots of foreign calls, you may
 355       need to tell the C&nbsp;compiler about some
 356       <literal>&num;include</literal> files.  There is no real pretty
 357       way to do this, but you can use this hack from the
 358       command-line:</para>
 359
 360 <Screen>
 361 % ghc -c '-#include &lt;X/Xlib.h&gt;' Xstuff.lhs
 362 </Screen>
 363
 364     </sect2>
 365
 366     <sect2 id="options-codegen">
 367       <title>Options affecting code generation</title>
 368
 369       <variablelist>
 370         <varlistentry>
 371           <term><option>-fasm</option></term>
 372           <indexterm><primary><option>-fasm</option></primary></indexterm>
 373           <listitem>
 374             <para>Use GHC's native code generator rather than
 375             compiling via C.  This will compile faster (up to twice as
 376             fast), but may produce code that is slightly slower than
 377             compiling via C.  <option>-fasm</option> is the default
 378             when optimisation is off (see <xref
 379             linkend="options-optimise">).</para>
 380           </listitem>
 381         </varlistentry>
 382
 383         <varlistentry>
 384           <term><option>-fvia-C</option></term>
 385           <indexterm><primary><option>-fvia-C</option></primary>
 386           </indexterm>
 387           <listitem>
 388             <para>Compile via C instead of using the native code
 389             generator.  This is default for optimised compilations,
 390             and on architectures for which GHC doesn't have a native
 391             code generator.</para>
 392           </listitem>
 393         </varlistentry>
 394
 395         <varlistentry>
 396           <term><option>-fno-code</option></term>
 397           <indexterm><primary><option>-fno-code</option></primary>
 398           </indexterm>
 399           <listitem>
 400             <para>Omit code generation (and all later phases)
 401             altogether.  Might be of some use if you just want to see
 402             dumps of the intermediate compilation phases.</para>
 403           </listitem>
 404         </varlistentry>
 405       </variablelist>
 406     </sect2>
 407
 408     <sect2 id="options-linker">
 409       <title>Options affecting linking</title>
 410
 411       <indexterm><primary>linker options</primary></indexterm>
 412       <indexterm><primary>ld options</primary></indexterm>
 413
 414
 415       <para>GHC has to link your code with various libraries, possibly
 416       including: user-supplied, GHC-supplied, and system-supplied
 417       (<option>-lm</option> math library, for example).</para>
 418
 419       <variablelist>
 420
 421         <varlistentry>
 422           <term><option>-l</option><replaceable>lib</replaceable></term>
 423           <indexterm><primary><option>-l</option></primary></indexterm>
 424           <listitem>
 425             <para>Link in the <replaceable>lib</replaceable> library.
 426             On Unix systems, this will be in a file called
 427             <filename>lib<replaceable>lib</replaceable>.a</filename>
 428             or
 429             <filename>lib<replaceable>lib</replaceable>.so</filename>
 430             which resides somewhere on the library directories path.</para>
 431
 432             <para>Because of the sad state of most UNIX linkers, the
 433             order of such options does matter.  If library
 434             <replaceable>foo</replaceable> requires library
 435             <replaceable>bar</replaceable>, then in general
 436             <option>-l</option><replaceable>foo</replaceable> should
 437             come <emphasis>before</emphasis>
 438             <option>-l</option><replaceable>bar</replaceable> on the
 439             command line.</para>
 440
 441             <para>There's one other gotcha to bear in mind when using
 442             external libraries: if the library contains a
 443             <literal>main()</literal> function, then this will be
 444             linked in preference to GHC's own
 445             <literal>main()</literal> function
 446             (eg. <literal>libf2c</literal> and <literal>libl</literal>
 447             have their own <literal>main()</literal>s).  This is
 448             because GHC's <literal>main()</literal> comes from the
 449             <literal>HSrts</literal> library, which is normally
 450             included <emphasis>after</emphasis> all the other
 451             libraries on the linker's command line.  To force GHC's
 452             <literal>main()</literal> to be used in preference to any
 453             other <literal>main()</literal>s from external libraries,
 454             just add the option <option>-lHSrts</option> before any
 455             other libraries on the command line.</para>
 456           </listitem>
 457         </varlistentry>
 458
 459         <varlistentry>
 460           <term><option>-package</option> <replaceable>name</replaceable></term>
 461           <indexterm><primary><option>-package</option></primary></indexterm>
 462           <listitem>
 463             <para>If you are using a Haskell &ldquo;package&rdquo;
 464             (see <xref linkend="packages">), don't forget to add the
 465             relevant <option>-package</option> option when linking the
 466             program too: it will cause the appropriate libraries to be
 467             linked in with the program.  Forgetting the
 468             <option>-package</option> option will likely result in
 469             several pages of link errors.</para>
 470           </listitem>
 471         </varlistentry>
 472
 473         <varlistentry>
 474           <term><option>-L</option><replaceable>dir</replaceable></term>
 475           <indexterm><primary><option>-L</option></primary></indexterm>
 476           <listitem>
 477             <para>Where to find user-supplied libraries&hellip;
 478             Prepend the directory <replaceable>dir</replaceable> to
 479             the library directories path.</para>
 480           </listitem>
 481         </varlistentry>
 482
 483         <varlistentry>
 484           <term><option>-split-objs</option></term>
 485           <indexterm><primary><option>-split-objs</option></primary></indexterm>
 486           <listitem>
 487             <para>Tell the linker to split the single object file that
 488             would normally be generated into multiple object files,
 489             one per top-level Haskell function or type in the module.
 490             We use this feature for building GHC's libraries libraries
 491             (warning: don't use it unless you know what you're
 492             doing!).</para>
 493           </listitem>
 494         </varlistentry>
 495
 496         <varlistentry>
 497           <term><option>-static</option></term>
 498           <indexterm><primary><option>-static</option></primary></indexterm>
 499           <listitem>
 500             <para>Tell the linker to avoid shared Haskell libraries,
 501             if possible.  This is the default.</para>
 502           </listitem>
 503         </varlistentry>
 504
 505         <varlistentry>
 506           <term><option>-dynamic</option></term>
 507           <indexterm><primary><option>-dynamic</option></primary></indexterm>
 508           <listitem>
 509             <para>Tell the linker to use shared Haskell libraries, if
 510             available (this option is only supported on Windows at the
 511             moment, and also note that your distribution of GHC may
 512             not have been supplied with shared libraries).</para>
 513           </listitem>
 514         </varlistentry>
 515
 516         <varlistentry>
 517           <term><option>-no-hs-main</option></term>
 518           <indexterm><primary><option>-no-hs-main</option></primary></indexterm>
 519           <indexterm><primary>linking Haskell libraries with foreign code</primary></indexterm>
 520           <listitem>
 521             <para>In the event you want to include ghc-compiled code
 522             as part of another (non-Haskell) program, the RTS will not
 523             be supplying its definition of <function>main()</function>
 524             at link-time, you will have to. To signal that to the
 525             driver script when linking, use
 526             <option>-no-hs-main</option>.</para>
 527
 528             <para>Notice that since the command-line passed to the
 529             linker is rather involved, you probably want to use
 530             <command>ghc</command> to do the final link of your
 531             `mixed-language' application. This is not a requirement
 532             though, just try linking once with <option>-v</option> on
 533             to see what options the driver passes through to the
 534             linker.</para>
 535           </listitem>
 536         </varlistentry>
 537       </variablelist>
 538     </sect2>
 539
 540   </sect1>
 541
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