1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <sect1 id="options-phases">
3 <title>Options related to a particular phase</title>
5 <sect2 id="replacing-phases">
6 <title>Replacing the program for one or more phases</title>
7 <indexterm><primary>phases, changing</primary></indexterm>
9 <para>You may specify that a different program be used for one
10 of the phases of the compilation system, in place of whatever
11 the <command>ghc</command> has wired into it. For example, you
12 might want to try a different assembler. The following options
13 allow you to change the external program used for a given
14 compilation phase:</para>
19 <option>-pgmL</option> <replaceable>cmd</replaceable>
20 <indexterm><primary><option>-pgmL</option></primary></indexterm>
23 <para>Use <replaceable>cmd</replaceable> as the literate
30 <option>-pgmP</option> <replaceable>cmd</replaceable>
31 <indexterm><primary><option>-pgmP</option></primary></indexterm>
34 <para>Use <replaceable>cmd</replaceable> as the C
35 pre-processor (with <option>-cpp</option> only).</para>
41 <option>-pgmc</option> <replaceable>cmd</replaceable>
42 <indexterm><primary><option>-pgmc</option></primary></indexterm>
45 <para>Use <replaceable>cmd</replaceable> as the C
52 <option>-pgmlo</option> <replaceable>cmd</replaceable>
53 <indexterm><primary><option>-pgmlo</option></primary></indexterm>
56 <para>Use <replaceable>cmd</replaceable> as the LLVM
63 <option>-pgmlc</option> <replaceable>cmd</replaceable>
64 <indexterm><primary><option>-pgmlc</option></primary></indexterm>
67 <para>Use <replaceable>cmd</replaceable> as the LLVM
74 <option>-pgmm</option> <replaceable>cmd</replaceable>
75 <indexterm><primary><option>-pgmm</option></primary></indexterm>
78 <para>Use <replaceable>cmd</replaceable> as the
85 <option>-pgms</option> <replaceable>cmd</replaceable>
86 <indexterm><primary><option>-pgms</option></primary></indexterm>
89 <para>Use <replaceable>cmd</replaceable> as the
96 <option>-pgma</option> <replaceable>cmd</replaceable>
97 <indexterm><primary><option>-pgma</option></primary></indexterm>
100 <para>Use <replaceable>cmd</replaceable> as the
107 <option>-pgml</option> <replaceable>cmd</replaceable>
108 <indexterm><primary><option>-pgml</option></primary></indexterm>
111 <para>Use <replaceable>cmd</replaceable> as the
118 <option>-pgmdll</option> <replaceable>cmd</replaceable>
119 <indexterm><primary><option>-pgmdll</option></primary></indexterm>
122 <para>Use <replaceable>cmd</replaceable> as the DLL
129 <option>-pgmF</option> <replaceable>cmd</replaceable>
130 <indexterm><primary><option>-pgmF</option></primary></indexterm>
133 <para>Use <replaceable>cmd</replaceable> as the
134 pre-processor (with <option>-F</option> only).</para>
140 <option>-pgmwindres</option> <replaceable>cmd</replaceable>
141 <indexterm><primary><option>-pgmwindres</option></primary></indexterm>
144 <para>Use <replaceable>cmd</replaceable> as the
145 program to use for embedding manifests on Windows. Normally this
146 is the program <literal>windres</literal>, which is supplied with a
147 GHC installation. See <option>-fno-embed-manifest</option> in <xref
148 linkend="options-linker" />.</para>
154 <sect2 id="forcing-options-through">
155 <title>Forcing options to a particular phase</title>
156 <indexterm><primary>forcing GHC-phase options</primary></indexterm>
158 <para>Options can be forced through to a particular compilation
159 phase, using the following flags:</para>
164 <option>-optL</option> <replaceable>option</replaceable>
165 <indexterm><primary><option>-optL</option></primary></indexterm>
168 <para>Pass <replaceable>option</replaceable> to the
169 literate pre-processor</para>
174 <option>-optP</option> <replaceable>option</replaceable>
175 <indexterm><primary><option>-optP</option></primary></indexterm>
178 <para>Pass <replaceable>option</replaceable> to CPP (makes
179 sense only if <option>-cpp</option> is also on).</para>
184 <option>-optF</option> <replaceable>option</replaceable>
185 <indexterm><primary><option>-optF</option></primary></indexterm>
188 <para>Pass <replaceable>option</replaceable> to the
189 custom pre-processor (see <xref linkend="pre-processor"/>).</para>
194 <option>-optc</option> <replaceable>option</replaceable>
195 <indexterm><primary><option>-optc</option></primary></indexterm>
198 <para>Pass <replaceable>option</replaceable> to the C compiler.</para>
203 <option>-optlo</option> <replaceable>option</replaceable>
204 <indexterm><primary><option>-optlo</option></primary></indexterm>
207 <para>Pass <replaceable>option</replaceable> to the LLVM optimiser.</para>
212 <option>-optlc</option> <replaceable>option</replaceable>
213 <indexterm><primary><option>-optlc</option></primary></indexterm>
216 <para>Pass <replaceable>option</replaceable> to the LLVM compiler.</para>
221 <option>-optm</option> <replaceable>option</replaceable>
222 <indexterm><primary><option>-optm</option></primary></indexterm>
225 <para>Pass <replaceable>option</replaceable> to the mangler.</para>
230 <option>-opta</option> <replaceable>option</replaceable>
231 <indexterm><primary><option>-opta</option></primary></indexterm>
234 <para>Pass <replaceable>option</replaceable> to the assembler.</para>
239 <option>-optl</option> <replaceable>option</replaceable>
240 <indexterm><primary><option>-optl</option></primary></indexterm>
243 <para>Pass <replaceable>option</replaceable> to the linker.</para>
248 <option>-optdll</option> <replaceable>option</replaceable>
249 <indexterm><primary><option>-optdll</option></primary></indexterm>
252 <para>Pass <replaceable>option</replaceable> to the DLL generator.</para>
257 <option>-optwindres</option> <replaceable>option</replaceable>
258 <indexterm><primary><option>-optwindres</option></primary></indexterm>
261 <para>Pass <replaceable>option</replaceable> to
262 <literal>windres</literal> when embedding manifests on Windows.
263 See <option>-fno-embed-manifest</option> in <xref
264 linkend="options-linker" />.</para>
269 <para>So, for example, to force an <option>-Ewurble</option>
270 option to the assembler, you would tell the driver
271 <option>-opta-Ewurble</option> (the dash before the E is
274 <para>GHC is itself a Haskell program, so if you need to pass
275 options directly to GHC's runtime system you can enclose them in
276 <literal>+RTS ... -RTS</literal> (see <xref
277 linkend="runtime-control"/>).</para>
281 <sect2 id="c-pre-processor">
282 <title>Options affecting the C pre-processor</title>
284 <indexterm><primary>pre-processing: cpp</primary></indexterm>
285 <indexterm><primary>C pre-processor options</primary></indexterm>
286 <indexterm><primary>cpp, pre-processing with</primary></indexterm>
292 <option>-cpp</option>
293 <indexterm><primary><option>-cpp</option></primary></indexterm>
296 <para>The C pre-processor <command>cpp</command> is run
297 over your Haskell code only if the <option>-cpp</option>
298 option <indexterm><primary>-cpp
299 option</primary></indexterm> is given. Unless you are
300 building a large system with significant doses of
301 conditional compilation, you really shouldn't need
308 <option>-D</option><replaceable>symbol</replaceable><optional>=<replaceable>value</replaceable></optional>
309 <indexterm><primary><option>-D</option></primary></indexterm>
312 <para>Define macro <replaceable>symbol</replaceable> in the
313 usual way. NB: does <emphasis>not</emphasis> affect
314 <option>-D</option> macros passed to the C compiler
315 when compiling via C! For those, use the
316 <option>-optc-Dfoo</option> hack… (see <xref
317 linkend="forcing-options-through"/>).</para>
323 <option>-U</option><replaceable>symbol</replaceable>
324 <indexterm><primary><option>-U</option></primary></indexterm>
327 <para> Undefine macro <replaceable>symbol</replaceable> in the
334 <option>-I</option><replaceable>dir</replaceable>
335 <indexterm><primary><option>-I</option></primary></indexterm>
338 <para> Specify a directory in which to look for
339 <literal>#include</literal> files, in the usual C
345 <para>The GHC driver pre-defines several macros when processing
346 Haskell source code (<filename>.hs</filename> or
347 <filename>.lhs</filename> files).</para>
349 <para>The symbols defined by GHC are listed below. To check which
350 symbols are defined by your local GHC installation, the following
351 trick is useful:</para>
353 <screen>$ ghc -E -optP-dM -cpp foo.hs
354 $ cat foo.hspp</screen>
356 <para>(you need a file <filename>foo.hs</filename>, but it isn't
357 actually used).</para>
362 <constant>__GLASGOW_HASKELL__</constant>
363 <indexterm><primary><constant>__GLASGOW_HASKELL__</constant></primary></indexterm>
367 <literal><replaceable>x</replaceable>.<replaceable>y</replaceable>.<replaceable>z</replaceable></literal>
369 <constant>__GLASGOW_HASKELL__</constant>
370 is the integer <replaceable>xyy</replaceable> (if
371 <replaceable>y</replaceable> is a single digit, then a leading zero
372 is added, so for example in version 6.2 of GHC,
373 <literal>__GLASGOW_HASKELL__==602</literal>). More
374 information in <xref linkend="version-numbering"/>.</para>
377 <constant>__GLASGOW_HASKELL__</constant>
378 will be undefined in all other implementations that
379 support C-style pre-processing.</para>
381 <para>(For reference: the comparable symbols for other
383 <constant>__HUGS__</constant>
385 <constant>__NHC__</constant>
387 <constant>__HBC__</constant>
390 <para>NB. This macro is set when pre-processing both
391 Haskell source and C source, including the C source
392 generated from a Haskell module
393 (i.e. <filename>.hs</filename>, <filename>.lhs</filename>,
394 <filename>.c</filename> and <filename>.hc</filename>
401 <constant>__PARALLEL_HASKELL__</constant>
402 <indexterm><primary><constant>__PARALLEL_HASKELL__</constant></primary></indexterm>
405 <para>Only defined when <option>-parallel</option> is in
406 use! This symbol is defined when pre-processing Haskell
407 (input) and pre-processing C (GHC output).</para>
413 <constant><replaceable>os</replaceable>_HOST_OS=1</constant>
416 <para>This define allows conditional compilation based on
417 the Operating System, where<replaceable>os</replaceable> is
418 the name of the current Operating System
419 (eg. <literal>linux</literal>, <literal>mingw32</literal>
420 for Windows, <literal>solaris</literal>, etc.).</para>
426 <constant><replaceable>arch</replaceable>_HOST_ARCH=1</constant>
429 <para>This define allows conditional compilation based on
430 the host architecture, where<replaceable>arch</replaceable>
431 is the name of the current architecture
432 (eg. <literal>i386</literal>, <literal>x86_64</literal>,
433 <literal>powerpc</literal>, <literal>sparc</literal>,
439 <sect3 id="cpp-string-gaps">
440 <title>CPP and string gaps</title>
442 <para>A small word of warning: <option>-cpp</option> is not
443 friendly to “string gaps”.<indexterm><primary>-cpp
444 vs string gaps</primary></indexterm><indexterm><primary>string
445 gaps vs -cpp</primary></indexterm>. In other words, strings
446 such as the following:</para>
448 <programlisting>strmod = "\
452 <para>don't work with <option>-cpp</option>;
453 <filename>/usr/bin/cpp</filename> elides the backslash-newline
456 <para>However, it appears that if you add a space at the end
457 of the line, then <command>cpp</command> (at least GNU
458 <command>cpp</command> and possibly other
459 <command>cpp</command>s) leaves the backslash-space pairs
460 alone and the string gap works as expected.</para>
464 <sect2 id="pre-processor">
465 <title>Options affecting a Haskell pre-processor</title>
467 <indexterm><primary>pre-processing: custom</primary></indexterm>
468 <indexterm><primary>Pre-processor options</primary></indexterm>
474 <indexterm><primary><option>-F</option></primary></indexterm>
477 <para>A custom pre-processor is run over your Haskell
478 source file only if the <option>-F</option> option
479 <indexterm><primary>-F</primary></indexterm> is
482 <para>Running a custom pre-processor at compile-time is in
483 some settings appropriate and useful. The
484 <option>-F</option> option lets you run a pre-processor as
485 part of the overall GHC compilation pipeline, which has
486 the advantage over running a Haskell pre-processor
487 separately in that it works in interpreted mode and you
488 can continue to take reap the benefits of GHC's
489 recompilation checker.</para>
491 <para>The pre-processor is run just before the Haskell
492 compiler proper processes the Haskell input, but after the
493 literate markup has been stripped away and (possibly) the
494 C pre-processor has washed the Haskell input.</para>
497 <option>-pgmF <replaceable>cmd</replaceable></option>
498 to select the program to use as the preprocessor. When
499 invoked, the <replaceable>cmd</replaceable> pre-processor
500 is given at least three arguments on its command-line: the
501 first argument is the name of the original source file,
502 the second is the name of the file holding the input, and
503 the third is the name of the file where
504 <replaceable>cmd</replaceable> should write its output
507 <para>Additional arguments to the pre-processor can be
508 passed in using the <option>-optF</option> option. These
509 are fed to <replaceable>cmd</replaceable> on the command
510 line after the three standard input and output
514 An example of a pre-processor is to convert your source files to the
515 input encoding that GHC expects, i.e. create a script
516 <literal>convert.sh</literal> containing the lines:
520 ( echo "{-# LINE 1 \"$2\" #-}" ; iconv -f l1 -t utf-8 $2 ) > $3</screen>
522 <para>and pass <literal>-F -pgmF convert.sh</literal> to GHC.
523 The <literal>-f l1</literal> option tells iconv to convert your
524 Latin-1 file, supplied in argument <literal>$2</literal>, while
525 the "-t utf-8" options tell iconv to return a UTF-8 encoded file.
526 The result is redirected into argument <literal>$3</literal>.
527 The <literal>echo "{-# LINE 1 \"$2\" #-}"</literal>
528 just makes sure that your error positions are reported as
529 in the original source file.</para>
535 <sect2 id="options-codegen">
536 <title>Options affecting code generation</title>
541 <option>-fasm</option>
542 <indexterm><primary><option>-fasm</option></primary></indexterm>
545 <para>Use GHC's native code generator rather than
546 compiling via C. This will compile faster (up to twice as
547 fast), but may produce code that is slightly slower than
548 compiling via C. <option>-fasm</option> is the default.</para>
554 <option>-fvia-C</option>
555 <indexterm><primary><option>-fvia-C</option></primary></indexterm>
558 <para>Compile via C instead of using the native code
559 generator. This is the default on architectures for which GHC
560 doesn't have a native code generator.</para>
566 <option>-fllvm</option>
567 <indexterm><primary><option>-fllvm</option></primary></indexterm>
570 <para>Compile via LLVM instead of using the native code
571 generator. This will generally take slightly longer than the
572 native code generator to compile but quicker than compiling
573 via C. Produced code is generally the same speed or faster
574 than the other two code generators. Compiling via LLVM
575 requires LLVM version 2.7 or later to be on the path.</para>
581 <option>-fno-code</option>
582 <indexterm><primary><option>-fno-code</option></primary></indexterm>
585 <para>Omit code generation (and all later phases)
586 altogether. Might be of some use if you just want to see
587 dumps of the intermediate compilation phases.</para>
593 <option>-fobject-code</option>
594 <indexterm><primary><option>-fobject-code</option></primary></indexterm>
597 <para>Generate object code. This is the default outside of
598 GHCi, and can be used with GHCi to cause object code to be
599 generated in preference to bytecode.</para>
605 <option>-fbyte-code</option>
606 <indexterm><primary><option>-fbyte-code</option></primary></indexterm>
609 <para>Generate byte-code instead of object-code. This is
610 the default in GHCi. Byte-code can currently only be used
611 in the interactive interpreter, not saved to disk. This
612 option is only useful for reversing the effect of
613 <option>-fobject-code</option>.</para>
619 <option>-fPIC</option>
620 <indexterm><primary><option>-fPIC</option></primary></indexterm>
623 <para>Generate position-independent code (code that can be put into
624 shared libraries). This currently works on Linux x86 and x86-64 when
625 using the native code generator (-fasm).
626 On Windows, position-independent code is never used
627 so the flag is a no-op on that platform.</para>
633 <option>-dynamic</option>
636 <para>When generating code, assume that entities imported from a
637 different package will reside in a different shared library or
639 <para>Note that using this option when linking causes GHC to link
640 against shared libraries.</para>
646 <sect2 id="options-linker">
647 <title>Options affecting linking</title>
649 <indexterm><primary>linker options</primary></indexterm>
650 <indexterm><primary>ld options</primary></indexterm>
653 <para>GHC has to link your code with various libraries, possibly
654 including: user-supplied, GHC-supplied, and system-supplied
655 (<option>-lm</option> math library, for example).</para>
661 <option>-l</option><replaceable>lib</replaceable>
662 <indexterm><primary><option>-l</option></primary></indexterm>
665 <para>Link in the <replaceable>lib</replaceable> library.
666 On Unix systems, this will be in a file called
667 <filename>lib<replaceable>lib</replaceable>.a</filename>
669 <filename>lib<replaceable>lib</replaceable>.so</filename>
670 which resides somewhere on the library directories path.</para>
672 <para>Because of the sad state of most UNIX linkers, the
673 order of such options does matter. If library
674 <replaceable>foo</replaceable> requires library
675 <replaceable>bar</replaceable>, then in general
676 <option>-l</option><replaceable>foo</replaceable> should
677 come <emphasis>before</emphasis>
678 <option>-l</option><replaceable>bar</replaceable> on the
681 <para>There's one other gotcha to bear in mind when using
682 external libraries: if the library contains a
683 <literal>main()</literal> function, then this will be
684 linked in preference to GHC's own
685 <literal>main()</literal> function
686 (eg. <literal>libf2c</literal> and <literal>libl</literal>
687 have their own <literal>main()</literal>s). This is
688 because GHC's <literal>main()</literal> comes from the
689 <literal>HSrts</literal> library, which is normally
690 included <emphasis>after</emphasis> all the other
691 libraries on the linker's command line. To force GHC's
692 <literal>main()</literal> to be used in preference to any
693 other <literal>main()</literal>s from external libraries,
694 just add the option <option>-lHSrts</option> before any
695 other libraries on the command line.</para>
702 <indexterm><primary><option>-c</option></primary></indexterm>
705 <para>Omits the link step. This option can be used with
706 <option>––make</option> to avoid the automatic linking
707 that takes place if the program contains a <literal>Main</literal>
714 <option>-package</option> <replaceable>name</replaceable>
715 <indexterm><primary><option>-package</option></primary></indexterm>
718 <para>If you are using a Haskell “package”
719 (see <xref linkend="packages"/>), don't forget to add the
720 relevant <option>-package</option> option when linking the
721 program too: it will cause the appropriate libraries to be
722 linked in with the program. Forgetting the
723 <option>-package</option> option will likely result in
724 several pages of link errors.</para>
730 <option>-framework</option> <replaceable>name</replaceable>
731 <indexterm><primary><option>-framework</option></primary></indexterm>
734 <para>On Darwin/MacOS X only, link in the framework <replaceable>name</replaceable>.
735 This option corresponds to the <option>-framework</option> option for Apple's Linker.
736 Please note that frameworks and packages are two different things - frameworks don't
737 contain any haskell code. Rather, they are Apple's way of packaging shared libraries.
738 To link to Apple's “Carbon” API, for example, you'd use
739 <option>-framework Carbon</option>.
746 <option>-L</option><replaceable>dir</replaceable>
747 <indexterm><primary><option>-L</option></primary></indexterm>
750 <para>Where to find user-supplied libraries…
751 Prepend the directory <replaceable>dir</replaceable> to
752 the library directories path.</para>
758 <option>-framework-path</option><replaceable>dir</replaceable>
759 <indexterm><primary><option>-framework-path</option></primary></indexterm>
762 <para>On Darwin/MacOS X only, prepend the directory <replaceable>dir</replaceable> to
763 the framework directories path. This option corresponds to the <option>-F</option>
764 option for Apple's Linker (<option>-F</option> already means something else for GHC).</para>
770 <option>-split-objs</option>
771 <indexterm><primary><option>-split-objs</option></primary></indexterm>
774 <para>Tell the linker to split the single object file that
775 would normally be generated into multiple object files,
776 one per top-level Haskell function or type in the module.
777 This only makes sense for libraries, where it means that
778 executables linked against the library are smaller as they only
779 link against the object files that they need. However, assembling
780 all the sections separately is expensive, so this is slower than
782 We use this feature for building GHC's libraries
783 (warning: don't use it unless you know what you're
790 <option>-static</option>
791 <indexterm><primary><option>-static</option></primary></indexterm>
794 <para>Tell the linker to avoid shared Haskell libraries,
795 if possible. This is the default.</para>
801 <option>-dynamic</option>
802 <indexterm><primary><option>-dynamic</option></primary></indexterm>
805 <para>This flag tells GHC to link against shared Haskell libraries.
806 This flag only affects the selection of dependent libraries, not
807 the form of the current target (see -shared).
808 See <xref linkend="using-shared-libs" /> on how to
811 <para>Note that this option also has an effect on
812 code generation (see above).</para>
818 <option>-shared</option>
819 <indexterm><primary><option>-shared</option></primary></indexterm>
822 <para>Instead of creating an executable, GHC produces a
823 shared object with this linker flag. Depending on the
824 operating system target, this might be an ELF DSO, a Windows
825 DLL, or a Mac OS dylib. GHC hides the operating system
826 details beneath this uniform flag.</para>
828 <para>The flags <option>-dynamic</option>/<option>-static</option> control whether the
829 resulting shared object links statically or dynamically to
830 Haskell package libraries given as <option>-package</option> option. Non-Haskell
831 libraries are linked as gcc would regularly link it on your
832 system, e.g. on most ELF system the linker uses the dynamic
833 libraries when found.</para>
835 <para>Object files linked into shared objects must be
836 compiled with <option>-fPIC</option>, see <xref linkend="options-codegen" /></para>
838 <para>When creating shared objects for Haskell packages, the
839 shared object must be named properly, so that GHC recognizes
840 the shared object when linked against this package. See
841 shared object name mangling.</para>
847 <option>-dynload</option>
848 <indexterm><primary><option>-dynload</option></primary></indexterm>
852 This flag selects one of a number of modes for finding shared
853 libraries at runtime. See <xref linkend="finding-shared-libs"/> for
854 a description of each mode.
861 <option>-main-is <replaceable>thing</replaceable></option>
862 <indexterm><primary><option>-main-is</option></primary></indexterm>
863 <indexterm><primary>specifying your own main function</primary></indexterm>
866 <para> The normal rule in Haskell is that your program must supply a <literal>main</literal>
867 function in module <literal>Main</literal>. When testing, it is often convenient
868 to change which function is the "main" one, and the <option>-main-is</option> flag
869 allows you to do so. The <replaceable>thing</replaceable> can be one of:
871 <listitem><para>A lower-case identifier <literal>foo</literal>. GHC assumes that the main function is <literal>Main.foo</literal>.</para></listitem>
872 <listitem><para>An module name <literal>A</literal>. GHC assumes that the main function is <literal>A.main</literal>.</para></listitem>
873 <listitem><para>An qualified name <literal>A.foo</literal>. GHC assumes that the main function is <literal>A.foo</literal>.</para></listitem>
875 Strictly speaking, <option>-main-is</option> is not a link-phase flag at all; it has no effect on the link step.
876 The flag must be specified when compiling the module containing the specified main function (e.g. module <literal>A</literal>
877 in the latter two items above). It has no effect for other modules,
878 and hence can safely be given to <literal>ghc --make</literal>.
879 However, if all the modules are otherwise up to date, you may need to force
880 recompilation both of the module where the new "main" is, and of the
881 module where the "main" function used to be;
882 <literal>ghc</literal> is not clever
883 enough to figure out that they both need recompiling. You can
884 force recompilation by removing the object file, or by using the
885 <option>-fforce-recomp</option> flag.
892 <option>-no-hs-main</option>
893 <indexterm><primary><option>-no-hs-main</option></primary></indexterm>
894 <indexterm><primary>linking Haskell libraries with foreign code</primary></indexterm>
897 <para>In the event you want to include ghc-compiled code
898 as part of another (non-Haskell) program, the RTS will not
899 be supplying its definition of <function>main()</function>
900 at link-time, you will have to. To signal that to the
901 compiler when linking, use
902 <option>-no-hs-main</option>. See also <xref linkend="using-own-main"/>.</para>
904 <para>Notice that since the command-line passed to the
905 linker is rather involved, you probably want to use
906 <command>ghc</command> to do the final link of your
907 `mixed-language' application. This is not a requirement
908 though, just try linking once with <option>-v</option> on
909 to see what options the driver passes through to the
912 <para>The <option>-no-hs-main</option> flag can also be
913 used to persuade the compiler to do the link step in
914 <option>--make</option> mode when there is no Haskell
915 <literal>Main</literal> module present (normally the
916 compiler will not attempt linking when there is no
917 <literal>Main</literal>).</para>
923 <option>-debug</option>
924 <indexterm><primary><option>-debug</option></primary></indexterm>
927 <para>Link the program with a debugging version of the
928 runtime system. The debugging runtime turns on numerous
929 assertions and sanity checks, and provides extra options
930 for producing debugging output at runtime (run the program
931 with <literal>+RTS -?</literal> to see a list).</para>
937 <option>-threaded</option>
938 <indexterm><primary><option>-threaded</option></primary></indexterm>
941 <para>Link the program with the "threaded" version of the
942 runtime system. The threaded runtime system is so-called
943 because it manages multiple OS threads, as opposed to the
944 default runtime system which is purely
945 single-threaded.</para>
947 <para>Note that you do <emphasis>not</emphasis> need
948 <option>-threaded</option> in order to use concurrency; the
949 single-threaded runtime supports concurrency between Haskell
950 threads just fine.</para>
952 <para>The threaded runtime system provides the following
957 <para>Parallelism<indexterm><primary>parallelism</primary></indexterm> on a multiprocessor<indexterm><primary>multiprocessor</primary></indexterm><indexterm><primary>SMP</primary></indexterm> or multicore<indexterm><primary>multicore</primary></indexterm>
958 machine. See <xref linkend="using-smp" />.</para>
960 <para>The ability to make a foreign call that does not
961 block all other Haskell threads, and to invoke
962 foreign-exported Haskell functions from multiple OS
963 threads. See <xref linkend="ffi-threads" />.</para>
971 <option>-eventlog</option>
972 <indexterm><primary><option>-eventlog</option></primary></indexterm>
976 Link the program with the "eventlog" version of the
977 runtime system. A program linked in this way can generate
978 a runtime trace of events (such as thread start/stop) to a
980 <literal><replaceable>program</replaceable>.eventlog</literal>,
981 which can then be interpreted later by various tools. See
982 <xref linkend="rts-eventlog" /> for more information.
985 <option>-eventlog</option> can be used
986 with <option>-threaded</option>. It is implied
987 by <option>-debug</option>.
994 <option>-fno-gen-manifest</option>
995 <indexterm><primary><option>-fno-gen-manifest</option></primary>
999 <para>On Windows, GHC normally generates a
1000 <firstterm>manifest</firstterm><indexterm><primary>manifest</primary>
1001 </indexterm>file when linking a binary. The
1002 manifest is placed in the file
1003 <literal><replaceable>prog</replaceable>.exe.manifest</literal>
1004 where <replaceable>prog.exe</replaceable> is the name of the
1005 executable. The manifest file currently serves just one purpose:
1006 it disables the "installer detection"<indexterm><primary>installer detection</primary>
1007 </indexterm>in Windows Vista that
1008 attempts to elevate privileges for executables with certain names
1009 (e.g. names containing "install", "setup" or "patch"). Without the
1010 manifest file to turn off installer detection, attempting to run an
1011 executable that Windows deems to be an installer will return a
1012 permission error code to the invoker. Depending on the invoker,
1013 the result might be a dialog box asking the user for elevated
1014 permissions, or it might simply be a permission denied
1017 <para>Installer detection can be also turned off globally for the
1018 system using the security control panel, but GHC by default
1019 generates binaries that don't depend on the user having disabled
1020 installer detection.</para>
1022 <para>The <option>-fno-gen-manifest</option> disables generation of
1023 the manifest file. One reason to do this would be if you had
1024 a manifest file of your own, for example.</para>
1026 <para>In the future, GHC might use the manifest file for more things,
1027 such as supplying the location of dependent DLLs.</para>
1029 <para><option>-fno-gen-manifest</option> also implies
1030 <option>-fno-embed-manifest</option>, see below.</para>
1036 <option>-fno-embed-manifest</option>
1037 <indexterm><primary><option>-fno-embed-manifest</option></primary>
1041 <para>The manifest file that GHC generates when linking a binary on
1042 Windows is also embedded in the executable itself, by default.
1043 This means that the binary can be distributed without having to
1044 supply the manifest file too. The embedding is done by running
1045 <literal>windres</literal><indexterm><primary><literal>windres</literal></primary>
1046 </indexterm>; to see exactly what GHC does to embed the manifest,
1047 use the <option>-v</option> flag. A GHC installation comes with
1048 its own copy of <literal>windres</literal> for this reason.</para>
1050 <para>See also <option>-pgmwindres</option> (<xref
1051 linkend="replacing-phases" />) and
1052 <option>-optwindres</option> (<xref
1053 linkend="forcing-options-through"
1060 <option>-fno-shared-implib</option>
1061 <indexterm><primary><option>-fno-shared-implib</option></primary>
1065 <para>DLLs on Windows are typically linked to by linking to a corresponding
1066 <literal>.lib</literal> or <literal>.dll.a</literal> - the so-called import library.
1067 GHC will typically generate such a file for every DLL you create by compiling in
1068 <literal>-shared</literal> mode. However, sometimes you don't want to pay the
1069 disk-space cost of creating this import library, which can be substantial - it
1070 might require as much space as the code itself, as Haskell DLLs tend to export
1071 lots of symbols.</para>
1073 <para>As long as you are happy to only be able to link to the DLL using
1074 <literal>GetProcAddress</literal> and friends, you can supply the
1075 <option>-fno-shared-implib</option> flag to disable the creation of the import
1076 library entirely.</para>
1082 <option>-dylib-install-name <replaceable>path</replaceable></option>
1083 <indexterm><primary><option>-dylib-install-name</option></primary>
1087 <para>On Darwin/MacOS X, dynamic libraries are stamped at build time with an
1088 "install name", which is the ultimate install path of the library file.
1089 Any libraries or executables that subsequently link against it will pick
1090 up that path as their runtime search location for it. By default, ghc sets
1091 the install name to the location where the library is built. This option
1092 allows you to override it with the specified file path. (It passes
1093 <literal>-install_name</literal> to Apple's linker.) Ignored on other
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