| 1 | =head1 NAME |
| 2 | |
| 3 | README.hints - hint files used by Configure |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 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. |
| 11 | |
| 12 | Please send any problems or suggested changes to |
| 13 | L<https://github.com/Perl/perl5/issues>. |
| 14 | |
| 15 | =head1 Hint file naming convention. |
| 16 | |
| 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. |
| 23 | |
| 24 | For example, consider Sun OS 4.1.3. Configure determines $osname=sunos |
| 25 | (all names are converted to lower case) and $osvers=4.1.3. Configure |
| 26 | will search for an appropriate hint file in the following order: |
| 27 | |
| 28 | sunos_4_1_3.sh |
| 29 | sunos_4_1.sh |
| 30 | sunos_4.sh |
| 31 | sunos.sh |
| 32 | |
| 33 | If you need to create a hint file, please try to use as general a name |
| 34 | as possible and include minor version differences inside case or test |
| 35 | statements. For example, for IRIX 6.X, we have the following hints |
| 36 | files: |
| 37 | |
| 38 | irix_6_0.sh |
| 39 | irix_6_1.sh |
| 40 | irix_6.sh |
| 41 | |
| 42 | That is, 6.0 and 6.1 have their own special hints, but 6.2, 6.3, and |
| 43 | up are all handled by the same irix_6.sh. That way, we don't have to |
| 44 | make a new hint file every time the IRIX O/S is upgraded. |
| 45 | |
| 46 | If you need to test for specific minor version differences in your |
| 47 | hints file, be sure to include a default choice. (See aix.sh for one |
| 48 | example.) That way, if you write a hint file for foonix 3.2, it might |
| 49 | still work without any changes when foonix 3.3 is released. |
| 50 | |
| 51 | Please also comment carefully on why the different hints are needed. |
| 52 | That way, a future version of Configure may be able to automatically |
| 53 | detect what is needed. |
| 54 | |
| 55 | A glossary of config.sh variables is in the file Porting/Glossary. |
| 56 | |
| 57 | =head1 Setting variables |
| 58 | |
| 59 | =head2 Optimizer |
| 60 | |
| 61 | If you want to set a variable, try to allow for Configure command-line |
| 62 | overrides. For example, suppose you think the default optimizer |
| 63 | setting to be -O2 for a particular platform. You should allow for |
| 64 | command line overrides with something like |
| 65 | |
| 66 | case "$optimize" in |
| 67 | '') optimize='-O2' ;; |
| 68 | esac |
| 69 | |
| 70 | or, if your system has a decent test(1) command, |
| 71 | |
| 72 | test -z "$optimize" && optimize='-O2' |
| 73 | |
| 74 | This allows the user to select a different optimization level, e.g. |
| 75 | -O6 or -g. |
| 76 | |
| 77 | =head2 Compiler and Linker flags |
| 78 | |
| 79 | If you want to set $ccflags or $ldflags, you should append to the existing |
| 80 | value to allow Configure command-line settings, e.g. use |
| 81 | |
| 82 | ccflags="$ccflags -DANOTHER_OPTION_I_NEED" |
| 83 | |
| 84 | so that the user can do something like |
| 85 | |
| 86 | sh Configure -Dccflags='FIX_NEGATIVE_ZERO' |
| 87 | |
| 88 | and have the FIX_NEGATIVE_ZERO value preserved by the hints file. |
| 89 | |
| 90 | =head2 Libraries |
| 91 | |
| 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. |
| 100 | |
| 101 | =head2 Other |
| 102 | |
| 103 | In general, try to avoid hard-wiring something that Configure will |
| 104 | figure out anyway. Also try to allow for Configure command-line |
| 105 | overrides. |
| 106 | |
| 107 | =head1 Working around compiler bugs |
| 108 | |
| 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 |
| 117 | |
| 118 | =head2 Test-case conventions |
| 119 | |
| 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. |
| 126 | |
| 127 | =head2 Hint file processing |
| 128 | |
| 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. |
| 134 | |
| 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 |
| 147 | possible. |
| 148 | |
| 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 |
| 152 | |
| 153 | pp_pack_cflags="optimize=-O0" or |
| 154 | pp_pack_cflags="optimize=" |
| 155 | |
| 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). |
| 165 | |
| 166 | You should also allow for the XXX_cflags variable to be overridden on the |
| 167 | command line. |
| 168 | |
| 169 | See the vos.sh hints file for an extended example of these techniques. |
| 170 | |
| 171 | =head1 Hint file tricks |
| 172 | |
| 173 | =head2 Printing critical messages |
| 174 | |
| 175 | [This is still experimental] |
| 176 | |
| 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. |
| 183 | |
| 184 | To use this feature, just do something like the following |
| 185 | |
| 186 | $cat <<EOM | $tee -a ../config.msg >&4 |
| 187 | |
| 188 | This is a really important message. Be sure to read it |
| 189 | before you type 'make'. |
| 190 | EOM |
| 191 | |
| 192 | This message will appear on the screen as the hint file is being |
| 193 | processed and again at the end of Configure. |
| 194 | |
| 195 | Please use this sparingly. |
| 196 | |
| 197 | =head2 Propagating variables to config.sh |
| 198 | |
| 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 |
| 202 | |
| 203 | toke_cflags='optimize=""' |
| 204 | |
| 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 $toke_cflags |
| 208 | and hence compile toke.c without optimization. |
| 209 | |
| 210 | Note that for this to work, the variable you want to propagate must |
| 211 | appear in the first column of the hint file. It is extracted by |
| 212 | Configure with a simple sed script, so beware that surrounding case |
| 213 | statements aren't any help. |
| 214 | |
| 215 | By contrast, if you don't want Configure to propagate your temporary |
| 216 | variable, simply indent it by a leading tab in your hint file. |
| 217 | |
| 218 | For example, prior to 5.002, a bug in scope.c led to perl crashing |
| 219 | when compiled with -O in AIX 4.1.1. The following "obvious" |
| 220 | workaround in hints/aix.sh wouldn't work as expected: |
| 221 | |
| 222 | case "$osvers" in |
| 223 | 4.1.1) |
| 224 | scope_cflags='optimize=""' |
| 225 | ;; |
| 226 | esac |
| 227 | |
| 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. |
| 231 | |
| 232 | Three possible fixes are: |
| 233 | |
| 234 | =over |
| 235 | |
| 236 | =item 1 |
| 237 | |
| 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. |
| 241 | |
| 242 | =item 2 |
| 243 | |
| 244 | Do the following trick: |
| 245 | |
| 246 | scope_cflags='case "$osvers" in 4.1*) optimize=" ";; esac' |
| 247 | |
| 248 | Now when $scope_cflags is eval'd by the cflags shell script, the |
| 249 | case statement is executed. Of course writing scripts to be eval'd is |
| 250 | tricky, especially if there is complex quoting. Or, |
| 251 | |
| 252 | =item 3 |
| 253 | |
| 254 | Write directly to Configure's temporary file UU/config.sh. |
| 255 | You can do this with |
| 256 | |
| 257 | case "$osvers" in |
| 258 | 4.1.1) |
| 259 | echo "scope_cflags='optimize=\"\"'" >> UU/config.sh |
| 260 | scope_cflags='optimize=""' |
| 261 | ;; |
| 262 | esac |
| 263 | |
| 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. |
| 266 | |
| 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. |
| 270 | |
| 271 | =back |
| 272 | |
| 273 | =head2 Call-backs |
| 274 | |
| 275 | =over 4 |
| 276 | |
| 277 | =item Compiler-related flags |
| 278 | |
| 279 | The settings of some things, such as optimization flags, may depend on |
| 280 | the particular compiler used. For example, consider the following: |
| 281 | |
| 282 | case "$cc" in |
| 283 | *gcc*) ccflags="$ccflags -posix" |
| 284 | ldflags="$ldflags -posix" |
| 285 | ;; |
| 286 | *) ccflags="$ccflags -Xp -D_POSIX_SOURCE" |
| 287 | ldflags="$ldflags -Xp" |
| 288 | ;; |
| 289 | esac |
| 290 | |
| 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. |
| 295 | |
| 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 |
| 305 | idea. |
| 306 | |
| 307 | =item Call status |
| 308 | |
| 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. |
| 313 | |
| 314 | =item Future status |
| 315 | |
| 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. |
| 320 | |
| 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. |
| 324 | |
| 325 | =back |
| 326 | |
| 327 | Have the appropriate amount of fun :-) |
| 328 | |
| 329 | Andy Dougherty doughera@lafayette.edu (author) |
| 330 | Paul Green paul.green@stratus.com (compiler bugs) |