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README - scc - simple c99 compiler
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README (7826B)
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1 Compiling
2 =========
3
4 SCC is a portable toolchain that can be compiled on any UNIX system
5 out of the box. It supports several configuration options that
6 can be passed to the command line:
7
8 - PREFIX: Prefix of the path where scc toolchain is going
9 to be installed. /usr/local by default.
10
11 - LIBPREFIX: Prefix of the path where scc searchs for
12 headers and libraries when scc is executed. $PREFIX
13 by default.
14
15 - DESTDIR: Temporary directory prepend to PREFIX used in the
16 install path. It is mainly intended to help package maintainers
17 to install in a specific directory used as base for the package
18 generation.
19
20 - CROSS_COMPILE:
21 Specify a prefix name for the tools called by the Makefile.
22
23 - HOST:
24 Specify the host system to be used. Possible supported
25 values are:
26
27 - unix (by default)
28 - bsd
29 - plan9
30
31 - CONF: Specify which version of libc to build.
32 Once the build process completes only the target specified in
33 CONF will be built. Supported values are:
34
35 - amd64-linux (default)
36 - amd64-darwin
37 - amd64-openbsd
38 - arm64-linux
39 - amd64-dragonfly
40 - amd64-freebsd
41 - amd64-netbsd
42 - arm32-linux
43 - i386-linux
44
45 Not all the configurations have the same level of support in
46 the libc and in some cases the support is minimal.
47
48 - TOOL: Specify the toolchain type to be used. Possible
49 supported values are:
50
51 - unix (by default)
52 - gnu
53 - gnu-darwin
54 - clang
55 - pcc
56 - plan9
57
58 Beware that the default target selects the appropiate value for HOST,
59 CONF and TOOL. In case of being needed, TOOL can be still overloaded
60 in the command line.
61
62 The main targets of the Makefile are:
63
64 - all:
65 Compile the toolchain and the libc. It automatically
66 determines what is the best value for HOST. It sets the
67 value of CONF for the toolchain that is used by the
68 toolchain as the default target. It also compiles the libc
69 for all the available configurations based in the host
70 architecture.
71
72 - config
73 Generate headers supposed to be customized by the user.
74
75 - toolchain
76 Compile the toolchain with the default configuration
77 specified in CONF. Beware that this target is executed without
78 the automatic detection of the host parameters. It makes
79 easier to cross compile.
80
81 - libc:
82 Compile the libc for the target specified in CONF. Beware
83 that this target is executed without the automatic detection
84 of the host parameters. It makes easier to cross compile.
85
86 - install:
87 Installs scc in PREFIX.
88
89 - clean:
90 Remove all the generated files except the one supposed to be edited
91 by the user.
92
93 - distclean
94 Remove all the generated files, including the files generated by the
95 config target that are not removed by the clean target.
96
97 Toolchain configuration
98 =======================
99 At this moment scc is still using some external tools to generate
100 the final binaries. The toolchain execution is configured in the
101 file `include/bits/scc/sys.h` and it included basically 5 elements:
102
103 - LDBIN: macro with the name of the linker binary.
104
105 - ASBIN: macro with the name of the assembler binary.
106
107 - sysincludes: It is a list of diretories used to locate
108 the system headers
109
110 - ldcmd: It describes how the linker command line is built.
111
112 - ascmd: It describes how the assembler command line is built.
113
114 The definition of sysincludes, ldcmd and ascmd can include wildcards
115 represented by % followed by a single letter:
116
117 - %c: It expands to the full list of input object files of the linker
118 - %a: It expands to the architecture name
119 - %s: It expands to the system name
120 - %p: It expands to the library prefix
121 - %b: It expands too the ABI name
122 - %o: It expands to the output file of the current tool
123
124 Scc includes 3 configuration templates that can be used as base for the
125 configuration of the toolchain:
126
127 - scc: It uses GNU assembler and linker with the scc libc.
128 - scc_clang: It uses clang assembler and linker with the scc libc.
129 - musl: It uses GNU assembler and linker with the musl libc.
130
131 The file `include/bits/scc/sys.h` is automatically created from the scc
132 toolchain configuration with the default make target. The target config
133 can be used to only create the file based on the value of the variable
134 `LIBPROFILE` allowing the user to customize that file as needed. It is
135 important to highlight that the file is not removed by `make clean`
136 because it can contain local user modifications. You should use
137 `make distclean` to remove it.
138
139 Runtime dependencies
140 ====================
141
142 Some configurations of scc require having the QBE [1] executable in the PATH,
143 whose version must support common storage which was incorporated to it after
144 the commit 8ded7a5, but it is not part of a stable release of QBE yet.
145
146 [1] https://c9x.me/compile/
147
148 Musl libc support
149 =================
150 The scc libc is a C99 library and cannot be used to compile POSIX compliant
151 programs. Scc includes a template that can be used to use a musl libc
152 compiled by gcc:
153
154 $ make LIBPROFILE=musl config
155
156 It will generate the files sys.h configured to be used with a musl
157 libc. Beware that it is likely that those files have to be customized to
158 fit your system because the macro GCCLIBPATH used by the musl template
159 depends heavily of the toolchain used to compile musl. As the musl libc
160 is likely installed in a different prefix the scc compilation must be
161 modified to:
162
163 $ make LIBPREFIX=/usr/local/musl # point to the prefix used by your musl
164
165 If the helper scc shell script is used instead of scc-cc then the
166 environment variable SCCLIBPREFIX must be set:
167
168 $ SCCLIBPREFIX=/usr/local/musl scc hello.c
169
170 Deviations from standard C
171 ===========================
172 This compiler aims to be fully compatible with the C99 standard, but
173 it has some differences at this moment:
174
175 - Type qualifiers are accepted but partially ignored.
176 --------------------------------------------------
177
178 The semantic behind them is not fully implemented, specially in the
179 case of volatile. Be aware that some programs can miswork for this
180 reason.
181
182 - Function type names
183 -------------------
184
185 C99 allows you to define type names of function types and write something
186 like:
187
188 int f(int (int));
189
190 Accepting function types in type names (or abstract declarators) makes the
191 grammar ambiguous because it is impossible to differentiate between:
192
193 (int (f)) -> function returning int with one parameter of type f
194 (int (f)) -> integer variable f
195
196 If you don't believe me try this code:
197
198 int
199 f(int g())
200 {
201 return g();
202 }
203
204 Function type names seem unnecesary , because they are used as
205 an alias of the function pointer types, but it is weird that something
206 like sizeof(int (int)) is not allowed (because here it should be
207 understood as the size of a function), but f(int (int)) is allowed
208 because it is understood as a parameter of function pointer type.
209
210 - Definition of variables with incomplete type
211 ---------------------------------------------
212
213 C89 allows the definition of variables with incomplete type that
214 have external linkage and file scope. The type of the variable is the
215 composition of all the definitions found in the file. The exact rules
216 are a bit complex (ANSI 3.7.2, or ISO C99 6.2.5p22) so SCC ignores them
217 at this moment by simply not allowing any definition of variables with
218 incomplete type.
219
220 If you don't believe me try this code:
221
222 struct foo x;
223
224 struct foo {
225 int i;
226 };
227
228 - Variadic function alike macros
229 ------------------------------
230
231 The standard (C99 6.10.3 c 4) forces passing more parameters than
232 the number of parameters present in the variadic argument list
233 (excluding ...). SCC accepts a parameter list with the same number
234 of arguments.
235
236 #define P(a, ...) a
237
238 P(1)
239
240 C99 libc
241 ========
242
243 The C99 libc only supports the C locale using UTF-8 for multibyte
244 sequences. It also assumes that the wide character set includes
245 ASCII as a subset.