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1 =head1 NAME
3 README.hints - hint files used by Configure
5 =head1 DESCRIPTION
7 These files are used by Configure to set things which Configure either
8 can't or doesn't guess properly. Most of these hint files have been
9 tested with at least some version of perl5, but some are still left
10 over from perl4.
12 Please report any problems or suggested changes at
15 =head1 Hint file naming convention.
17 Each hint file name should have only
18 one '.'. (This is for portability to non-unix file systems.) Names
19 should also fit in <= 14 characters, for portability to older SVR3
20 systems. File names are of the form $osname_$osvers.sh, with all '.'
21 changed to '_', and all characters (such as '/') that don't belong in
22 Unix filenames omitted.
24 For example, consider Sun OS 4.1.3. Configure determines $osname=sunos
25 (all names are converted to lower case) and $osvers=4.1.3. Configure
26 will search for an appropriate hint file in the following order:
33 If you need to create a hint file, please try to use as general a name
34 as possible and include minor version differences inside case or test
35 statements. For example, for IRIX 6.X, we have the following hints
42 That is, 6.0 and 6.1 have their own special hints, but 6.2, 6.3, and
43 up are all handled by the same irix_6.sh. That way, we don't have to
44 make a new hint file every time the IRIX O/S is upgraded.
46 If you need to test for specific minor version differences in your
47 hints file, be sure to include a default choice. (See aix.sh for one
48 example.) That way, if you write a hint file for foonix 3.2, it might
49 still work without any changes when foonix 3.3 is released.
51 Please also comment carefully on why the different hints are needed.
52 That way, a future version of Configure may be able to automatically
53 detect what is needed.
55 A glossary of config.sh variables is in the file Porting/Glossary.
57 =head1 Setting variables
59 =head2 Optimizer
61 If you want to set a variable, try to allow for Configure command-line
62 overrides. For example, suppose you think the default optimizer
63 setting to be -O2 for a particular platform. You should allow for
64 command line overrides with something like
66 case "$optimize" in
67 '') optimize='-O2' ;;
70 or, if your system has a decent test(1) command,
72 test -z "$optimize" && optimize='-O2'
74 This allows the user to select a different optimization level, e.g.
75 -O6 or -g.
77 =head2 Compiler and Linker flags
79 If you want to set $ccflags or $ldflags, you should append to the existing
80 value to allow Configure command-line settings, e.g. use
82 ccflags="$ccflags -DANOTHER_OPTION_I_NEED"
84 so that the user can do something like
86 sh Configure -Dccflags='FIX_NEGATIVE_ZERO'
88 and have the FIX_NEGATIVE_ZERO value preserved by the hints file.
90 =head2 Libraries
92 Configure will attempt to use the libraries listed in the variable
93 $libswanted. If necessary, you should remove broken libraries from
94 that list, or add additional libraries to that list. You should
95 *not* simply set $libs -- that ignores the possibilities of local
96 variations. For example, a setting of libs='-lgdbm -lm -lc' would
97 fail if another user were to try to compile Perl on a system without
98 GDBM but with Berkeley DB. See hints/dec_osf.sh and hints/solaris_2.sh
99 for examples.
101 =head2 Other
103 In general, try to avoid hard-wiring something that Configure will
104 figure out anyway. Also try to allow for Configure command-line
107 =head1 Working around compiler bugs
109 Occasionally, the root cause of a bug in perl turns out to be due to a bug
110 in the compiler. Often, changing the compilation options (particularly the
111 optimization level) can work around the bug. However, if you try to do
112 this on the command line, you will be changing the compilation options for
113 every component of perl, which can really hurt perl's performance.
114 Instead, consider placing a test case into the hints directory to detect
115 whether the compiler bug is present, and add logic to the hints file to
116 take a specific and appropriate action
118 =head2 Test-case conventions
120 Test cases should be named "tNNN.c", where NNN is the next unused sequence
121 number. The test case must be executable and should display a message
122 containing the word "fails" when the compiler bug is present. It should
123 display the word "works" with the compiler bug is not present. The test
124 cases should be liberally commented and may be used by any hints file that
125 needs them. See the first hints file (t001.c) for an example.
127 =head2 Hint file processing
129 The hint file must define a call-back unit (see below) that will compile,
130 link, and run the test case, and then check for the presence of the string
131 "fails" in the output. If it finds this string, it sets a special variable
132 to specify the compilation option(s) for the specific perl source file that
133 is affected by the bug.
135 The special variable is named "XXX_cflags" where "XXX" is the name of
136 the source file (without the ".c" suffix). The value of this variable
137 is the string "optimize=YYY", where "YYY" is the compilation option
138 necessary to work around the bug. The default value of this variable
139 is "-O" (letter O), which specifies that the C compiler should compile
140 the source program at the default optimization level. If you can
141 avoid the compiler bug by disabling optimization, just reset the
142 "optimize" variable to the null string. Sometimes a bug is present at
143 a higher optimization level (say, O3) and not present at a lower
144 optimization level (say, O1). In this case, you should specify the
145 highest optimization level at which the bug is not present, so that
146 you will retain as many of the benefits of code optimization as
149 For example, if the pp_pack.c source file must be compiled at
150 optimization level 0 to work around a problem on a particular
151 platform, one of the statements
153 pp_pack_cflags="optimize=-O0" or
156 will do the trick, since level 0 is equivalent to no optimization.
157 (In case your printer or display device does not distinguish the
158 letter O from the digit 0, that is the letter O followed by the digit
159 0). You can specify any compiler option or set of options here, not
160 just optimizer options. These options are appended to the list of all
161 other compiler options, so you should be able to override almost any
162 compiler option prepared by Configure. (Obviously this depends on how
163 the compiler treats conflicting options, but most seem to go with the
164 last value specified on the command line).
166 You should also allow for the XXX_cflags variable to be overridden on the
167 command line.
169 See the vos.sh hints file for an extended example of these techniques.
171 =head1 Hint file tricks
173 =head2 Printing critical messages
175 [This is still experimental]
177 If you have a *REALLY* important message that the user ought to see at
178 the end of the Configure run, you can store it in the file
179 'config.msg'. At the end of the Configure run, Configure will display
180 the contents of this file. Currently, the only place this is used is
181 in Configure itself to warn about the need to set LD_LIBRARY_PATH if
182 you are building a shared libperl.so.
184 To use this feature, just do something like the following
186 $cat <<EOM | $tee -a ../config.msg >&4
188 This is a really important message. Be sure to read it
189 before you type 'make'.
192 This message will appear on the screen as the hint file is being
193 processed and again at the end of Configure.
195 Please use this sparingly.
197 =head2 Propagating variables to config.sh
199 Sometimes, you want an extra variable to appear in config.sh. For
200 example, if your system can't compile toke.c with the optimizer on,
201 you can put
205 at the beginning of a line in your hints file. Configure will then
206 extract that variable and place it in your config.sh file. Later,
207 while compiling toke.c, the cflags shell script will eval $toke_cflags
208 and hence compile toke.c without optimization.
210 Note that for this to work, the variable you want to propagate must
211 appear in the first column of the hint file. It is extracted by
212 Configure with a simple sed script, so beware that surrounding case
213 statements aren't any help.
215 By contrast, if you don't want Configure to propagate your temporary
216 variable, simply indent it by a leading tab in your hint file.
218 For example, prior to 5.002, a bug in scope.c led to perl crashing
219 when compiled with -O in AIX 4.1.1. The following "obvious"
220 workaround in hints/aix.sh wouldn't work as expected:
222 case "$osvers" in
228 because Configure doesn't parse the surrounding 'case' statement, it
229 just blindly propagates any variable that starts in the first column.
230 For this particular case, that's probably harmless anyway.
232 Three possible fixes are:
236 =item 1
238 Create an aix_4_1_1.sh hint file that contains the scope_cflags
239 line and then sources the regular aix hints file for the rest of
240 the information.
242 =item 2
244 Do the following trick:
246 scope_cflags='case "$osvers" in 4.1*) optimize=" ";; esac'
248 Now when $scope_cflags is eval'd by the cflags shell script, the
249 case statement is executed. Of course writing scripts to be eval'd is
250 tricky, especially if there is complex quoting. Or,
252 =item 3
254 Write directly to Configure's temporary file UU/config.sh.
255 You can do this with
257 case "$osvers" in
259 echo "scope_cflags='optimize=\"\"'" >> UU/config.sh
264 Note you have to both write the definition to the temporary
265 UU/config.sh file and set the variable to the appropriate value.
267 This is sneaky, but it works. Still, if you need anything this
268 complex, perhaps you should create the separate hint file for
269 aix 4.1.1.
273 =head2 Call-backs
275 =over 4
277 =item Compiler-related flags
279 The settings of some things, such as optimization flags, may depend on
280 the particular compiler used. For example, consider the following:
282 case "$cc" in
283 *gcc*) ccflags="$ccflags -posix"
284 ldflags="$ldflags -posix"
286 *) ccflags="$ccflags -Xp -D_POSIX_SOURCE"
287 ldflags="$ldflags -Xp"
291 However, the hints file is processed before the user is asked which
292 compiler should be used. Thus in order for these hints to be useful,
293 the user must specify sh Configure -Dcc=gcc on the command line, as
294 advised by the INSTALL file.
296 For versions of perl later than 5.004_61, this problem can
297 be circumvented by the use of "call-back units". That is, the hints
298 file can tuck this information away into a file UU/cc.cbu. Then,
299 after Configure prompts the user for the C compiler, it will load in
300 and run the UU/cc.cbu "call-back" unit. See hints/solaris_2.sh for an
301 example. Some callbacks exist for other variables than cc, such as for
302 uselongdouble. At the present time, these callbacks are only called if the
303 variable in question is defined; however, this may change, so the scheme in
304 hints/solaris_2.sh of checking to see if uselongdouble is defined is a good
307 =item Call status
309 Call-backs are only called always, even if the value for the call-back is
310 uset: UU/usethreads.cbu is called when Configure is about to deal with
311 threads. All created call-backs from hints should thus check the status
312 of the variable, and act upon it.
314 =item Future status
316 I hope this "call-back" scheme is simple enough to use but powerful
317 enough to deal with most situations. Still, there are certainly cases
318 where it's not enough. For example, for aix we actually change
319 compilers if we are using threads.
321 I'd appreciate feedback on whether this is sufficiently general to be
322 helpful, or whether we ought to simply continue to require folks to
323 say things like "sh Configure -Dcc=gcc -Dusethreads" on the command line.
327 Have the appropriate amount of fun :-)
329 Andy Dougherty email@example.com (author)
330 Paul Green firstname.lastname@example.org (compiler bugs)