1 ;;;; tags which are set during the build process and which end up in
2 ;;;; CL:*FEATURES* in the target SBCL, plus some comments about other
3 ;;;; CL:*FEATURES* tags which have special meaning to SBCL or which
4 ;;;; have a special conventional meaning
6 ;;;; This software is part of the SBCL system. See the README file for
9 ;;;; This software is derived from the CMU CL system, which was
10 ;;;; written at Carnegie Mellon University and released into the
11 ;;;; public domain. The software is in the public domain and is
12 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
13 ;;;; files for more information.
17 ;; features present in all builds
22 ;; FIXME: Isn't there a :x3jsomething feature which we should set too?
27 ;; Douglas Thomas Crosher's conservative generational GC (the only one
28 ;; we currently support)
31 ;; We're running under a UNIX. This is sort of redundant, and it was also
32 ;; sort of redundant under CMU CL, which we inherited it from: neither SBCL
33 ;; nor CMU CL supports anything but UNIX (and "technically not UNIX"es
34 ;; such as *BSD and Linux). But someday, maybe we might, and in that case
35 ;; we'd presumably remove this, so its presence conveys the information
36 ;; that the system isn't one which follows such a change.
40 ;; features present in this particular build
43 ;; Setting this enables the compilation of documentation strings
44 ;; from the system sources into the target Lisp executable.
45 ;; Traditional Common Lisp folk will want this option set.
46 ;; I (WHN) made it optional because I came to Common Lisp from
47 ;; C++ through Scheme, so I'm accustomed to asking
48 ;; Emacs about things that I'm curious about instead of asking
49 ;; the executable I'm running.
52 ;; When this is set, EVAL is implemented as an "IR1 interpreter":
53 ;; code is compiled into the compiler's first internal representation,
54 ;; then the IR1 is interpreted. When this is not set, EVAL is implemented
55 ;; as a little bit of hackery wrapped around a call to COMPILE, i.e.
56 ;; the system becomes a "compiler-only implementation" of Common Lisp.
57 ;; As of sbcl-0.6.7, the compiler-only implementation is prototype code,
58 ;; and much less mature than the old IR1 interpreter. Thus, the safe
59 ;; thing is to leave :SB-INTERPRETER set. However, the compiler-only
60 ;; system is noticeably smaller, so you might want to omit
61 ;; :SB-INTERPRETER if you have a small machine.
63 ;; Probably, the compiler-only implementation will become more
64 ;; stable someday, and support for the IR1 interpreter will then be
65 ;; dropped. This will make the system smaller and easier to maintain
66 ;; not only because we no longer need to support the interpreter,
67 ;; but because code elsewhere in the system (the dumper, the debugger,
68 ;; etc.) no longer needs special cases for interpreted code.
71 ;; Do regression and other tests when building the system. You
72 ;; might or might not want this if you're not a developer,
73 ;; depending on how paranoid you are. You probably do want it if
74 ;; you are a developer.
77 ;; Setting this makes more debugging information available.
78 ;; If you aren't hacking or troubleshooting SBCL itself, you
79 ;; probably don't want this set.
81 ;; At least two varieties of debugging information are enabled by this
83 ;; * SBCL is compiled with a higher level of OPTIMIZE DEBUG, so that
84 ;; the debugger can tell more about the state of the system.
85 ;; * Various code to print debugging messages, and similar debugging code,
86 ;; is compiled only when this feature is present.
88 ;; Note that the extra information recorded by the compiler at
89 ;; this higher level of OPTIMIZE DEBUG includes the source location
90 ;; forms. In order for the debugger to use this information, it has to
91 ;; re-READ the source file. In an ordinary installation of SBCL, this
92 ;; re-READing may not work very well, for either of two reasons:
93 ;; * The sources aren't present on the system in the same location that
94 ;; they were on the system where SBCL was compiled.
95 ;; * SBCL is using the standard readtable, without the added hackage
96 ;; which allows it to handle things like target features.
97 ;; If you want to be able to use the extra debugging information,
98 ;; therefore, be sure to keep the sources around, and run with the
99 ;; readtable configured so that the system sources can be read.
102 ;; Enable extra debugging output in the assem.lisp assembler/scheduler
103 ;; code. (This is the feature which was called :DEBUG in the
104 ;; original CMU CL code.)
107 ;; Setting this makes SBCL more "fluid", i.e. more amenable to
108 ;; modification at runtime, by suppressing various INLINE declarations,
109 ;; compiler macro definitions, FREEZE-TYPE declarations; and by
110 ;; suppressing various burning-our-ships-behind-us actions after
111 ;; initialization is complete; and so forth. This tends to clobber the
112 ;; performance of the system, so unless you have some special need for
113 ;; this when hacking SBCL itself, you don't want this set.
116 ;; Enable code for collecting statistics on usage of various operations,
117 ;; useful for performance tuning of the SBCL system itself. This code
118 ;; is probably pretty stale (having not been tested since the fork from
119 ;; base CMU CL) but might nonetheless be a useful starting point for
120 ;; anyone who wants to collect such statistics in the future.
123 ;; Peter Van Eynde's increase-bulletproofness code
125 ;; This is not maintained or tested in current SBCL, but I haven't
126 ;; gone out of my way to remove or break it, either.
129 ; :high-security-support
131 ;; multiprocessing support
133 ;; This is not maintained or tested in current SBCL. I haven't gone out
134 ;; of my way to break it, but since it's derived from an old version of
135 ;; CMU CL where multiprocessing was pretty shaky, it's likely to be very
137 ;; :MP enables multiprocessing
138 ;; :MP-I486 is used, only within the multiprocessing code, to control
139 ;; what seems to control processor-version-specific code. It's
140 ;; probably for 486 or later, i.e. could be set as long as
141 ;; you know you're not running on a 386, but it doesn't seem
142 ;; to be documented anywhere, so that's just a guess.
146 ;; KLUDGE: used to suppress stale code related to floating point infinities.
147 ;; I intend to delete this code completely some day, since it was a pain
148 ;; for me to try to work with and since all benefits it provides are
149 ;; non-portable. Until I actually pull the trigger, though, I've left
150 ;; various stale code in place protected with #!-SB-INFINITIES.
153 ;; This affects the definition of a lot of things in bignum.lisp. It
154 ;; doesn't seem to be documented anywhere what systems it might apply to.
155 ;; It doesn't seem to be needed for X86 systems anyway.
158 ;; This is probably true for some processor types, but not X86. It affects
159 ;; a lot of floating point code.
160 ; :negative-zero-is-not-zero
162 ;; This is mentioned in cmu-user.tex, which says that it enables
163 ;; the compiler to reason about integer arithmetic. It also seems to
164 ;; control other fancy numeric reasoning, e.g. knowing the result type of
165 ;; a remainder calculation given the type of its inputs.
167 ;; KLUDGE: Even when this is implemented for the target feature list,
168 ;; the code to implement this feature will not generated in the
169 ;; cross-compiler (i.e. will only be generated in the target compiler).
170 ;; The reason for this is that the interval arithmetic routines used
171 ;; to implement this feature are written under the assumption that
172 ;; Lisp arithmetic supports plus and minus infinity, which isn't guaranteed by
173 ;; ANSI Common Lisp. I've tried to mark the conditionals which implement
174 ;; this kludge with the string CROSS-FLOAT-INFINITY-KLUDGE so that
175 ;; sometime it might be possible to undo them (perhaps by using
176 ;; nice portable :PLUS-INFINITY and :MINUS-INFINITY values instead of
177 ;; implementation dependent floating infinity values, which would
178 ;; admittedly involve extra consing; or perhaps by finding some cleaner
179 ;; way of suppressing the construction of this code in the cross-compiler).
181 ;; KLUDGE: Even after doing the KLUDGE above, the cross-compiler doesn't work,
182 ;; because some interval operations are conditional on PROPAGATE-FUN-TYPE
183 ;; instead of PROPAGATE-FLOAT-TYPE. So for now, I've completely turned off
184 ;; both PROPAGATE-FUN-TYPE and PROPAGATE-FLOAT-TYPE. (After I build
185 ;; a compiler which works, then I can think about getting the optimization
186 ;; to work.) -- WHN 19990702
187 ; :propagate-float-type
189 ;; According to cmu-user.tex, this enables the compiler to infer result
190 ;; types for mathematical functions like SQRT, EXPT, and LOG, allowing
191 ;; it to e.g. eliminate the possibility that a complex result will be
194 ;; KLUDGE: turned off as per the comments for PROPAGATE-FLOAT-TYPE above
195 ; :propagate-fun-type
197 ;; It's unclear to me what this does (but it was enabled in the code that I
198 ;; picked up from Peter Van Eynde). -- WHN 19990224
199 :constrain-float-type
201 ;; This is set in classic CMU CL, and presumably there it means
202 ;; that the floating point arithmetic implementation
203 ;; conforms to IEEE's standard. Here it definitely means that the
204 ;; floating point arithmetic implementation conforms to IEEE's standard.
205 ;; I (WHN 19990702) haven't tried to verify
206 ;; that it does conform, but it should at least mostly conform (because
207 ;; the underlying x86 hardware tries).
210 ;; This seems to be the pre-GENCGC garbage collector for CMU CL, which was
211 ;; AFAIK never supported for the X86.
214 ;; CMU CL had, and we inherited, code to support 80-bit LONG-FLOAT on the x86
215 ;; architecture. Nothing has been done to actively destroy the long float
216 ;; support, but it hasn't been thoroughly maintained, and needs at least
217 ;; some maintenance before it will work. (E.g. the LONG-FLOAT-only parts of
218 ;; genesis are still implemented in terms of unportable CMU CL functions
219 ;; which are not longer available at genesis time in SBCL.) A deeper
220 ;; problem is SBCL's bootstrap process implicitly assumes that the
221 ;; cross-compilation host will be able to make the same distinctions
222 ;; between floating point types that it does. This assumption is
223 ;; fundamentally sleazy, even though in practice it's unlikely to break down
224 ;; w.r.t. distinguishing SINGLE-FLOAT from DOUBLE-FLOAT; it's much more
225 ;; likely to break down w.r.t. distinguishing DOUBLE-FLOAT from LONG-FLOAT.
226 ;; Still it's likely to be quite doable to get LONG-FLOAT support working
227 ;; again, if anyone's sufficiently motivated.
231 ;; miscellaneous notes on other things which could have special significance
232 ;; in the *FEATURES* list
235 ;; notes on the :NIL and :IGNORE features:
237 ;; #+NIL is used to comment out forms. Occasionally #+IGNORE is used
238 ;; for this too. So don't use :NIL or :IGNORE as the names of features..
240 ;; notes on :SB-XC and :SB-XC-HOST features (which aren't controlled by this
241 ;; file, but are instead temporarily pushed onto *FEATURES* or
242 ;; *TARGET-FEATURES* during some phases of cross-compilation):
244 ;; :SB-XC-HOST stands for "cross-compilation host" and is in *FEATURES*
245 ;; during the first phase of cross-compilation bootstrapping, when the
246 ;; host Lisp is being used to compile the cross-compiler.
248 ;; :SB-XC stands for "cross compiler", and is in *FEATURES* during the second
249 ;; phase of cross-compilation bootstrapping, when the cross-compiler is
250 ;; being used to create the first target Lisp.
252 ;; notes on the :SB-ASSEMBLING feature (which isn't controlled by
255 ;; This is a flag for whether we're in the assembler. It's
256 ;; temporarily pushed onto the *FEATURES* list in the setup for
257 ;; the ASSEMBLE-FILE function. It would be a bad idea
258 ;; to use it as a name for a permanent feature.
260 ;; notes on local features (which are set automatically by the
261 ;; configuration script, and should not be set here unless you
262 ;; really, really know what you're doing):
264 ;; machine architecture features:
265 ;; :x86 ; any Intel 386 or better, or compatibles like the AMD K6 or K7
266 ;; (No others are supported by SBCL as of 0.6.7, but :alpha or
267 ;; :sparc support could be ported from CMU CL if anyone is
268 ;; sufficiently motivated to do so.)
269 ;; (CMU CL also had a :pentium feature, which affected the definition
270 ;; of some floating point vops. It was present but not enabled in the
271 ;; CMU CL code that SBCL is derived from, and is present but stale
272 ;; in SBCL as of 0.6.7.)
274 ;; operating system features:
275 ;; :linux = We're intended to run under some version of Linux.
276 ;; :bsd = We're intended to run under some version of BSD Unix. (This
277 ;; is not exclusive with the features which indicate which
278 ;; particular version of BSD we're intended to run under.)
279 ;; :freebsd = We're intended to run under FreeBSD.
280 ;; :openbsd = We're intended to run under FreeBSD.
281 ;; (No others are supported by SBCL as of 0.6.7, but :hpux or
282 ;; :solaris support could be ported from CMU CL if anyone is
283 ;; sufficiently motivated to do so.)