This source file is part of the SubC compiler, which is described in the book
Practical Compiler Construction.
You might prefer to download the compiler source code. It is in the public domain.
SubC Compiler, Version 2014-04-25
By Nils M Holm, 2011--2014
Placed in the public domain
SUMMARY
SubC is a compiler for a (mostly) strict and sane subset of
C as described in "The C Programming Language", 2nd Ed (also
known informally as "ANSI C" or "C89").
A previous version of the compiler is described in great detail
in the book "Practical Compiler Construction", which can be
purchased at Lulu.com. See http://www.t3x.org/reload/ for
ordering information.
The SubC compiler can compile itself. Unlike many other small C
compilers, it does not bend the rules, though. Its code passes
"gcc -Wall -pedantic" with little or no warnings (depending on
the gcc version used). Of course, you can also bootstrap it with
other C compilers, such as Clang or PCC.
SubC is fast and simple. Its output is typically small (due to
a non-bloated library), but not very runtime-efficient, because
it employs none of the optimization strategies explained in the
book.
SUPPORTED SYSTEMS
SubC generates code for GAS, the GNU assembler (except for the
DOS version, which emits TASM-style syntax). It targets the
following processors and operating systems:
FreeBSD 386+ armv6+ x86-64
Linux 386+* - x86-64+*
NetBSD - - x86-64
OpenBSD 386* - -
Windows/MinGW 386* - -
Darwin - - x86-64*
DOS 8086+!
+ does *not* use the syscall layer of the host libc
* untested
! experimental
Platforms tagged "untested" are not regularly tested by myself
and are therefore subject to potential bit rot. You can help
me improve SubC by running "make tests" on an "untested"
platform and inform me about the result.
Porting SubC to other 32-bit or 64-bit platforms should be
quite straight-forward. See the file "Porting" and/or the book
for a general road map.
The DOS version brings its own toolchain, which can be found in
the s86/ directory, so no pre-existing DOS assembler or linker
is required to compile SubC programs on DOS.
CHANGES TO THE BOOK VERSION
Note: The book version runs on FreeBSD/386 exclusively.
The current version uses an improved code generator, which
emits about 10% smaller and 20% faster code than the compiler
described in the book.
This version of the SubC compiler adds support for the
following parts of C language to the version described in
"Practical Compiler Construction":
o &array is now valid syntax (you no longer have to write
&array[0]).
o the auto, register, and volatile keywords are recognized
(as no-ops). Yes, volatile is safe, because SubC does not
have register variables.
o enums may now be local.
o extern identifiers may now be declared locally.
o Prototypes may have the static storage class.
o There is support for structs and unions.
o jmp_buf is now a struct; setjmp() and longjmp() must be
called with &jmp_buf.
o FILEs are now structs and can no longer be mistaken for
ints by the type checker.
o The #error, #line, and #pragma commands have been added.
o There is a (non-standard) kprintf() function, which is
like fprintf(), but uses a file descriptor.
o There is now a (slightly incompatible) varargs mechanism.
Here is how it works:
#include <varargs.h>
void p(void *last, ...) {
void *ap;
int first;
ap = _va_start(&last);
first = (int) _va_arg(&ap);
vprintf("other args: %d %d %d\n", ap);
_va_end(&ap);
}
int p(int x, int y, ...);
There may only be one argument in front of the "...", but
the signature of the function can later be modified with a
prototype.
o The vprintf(), vfprintf(), and vsprintf() functions have
been added to the runtime library.
DIFFERENCES BETWEEN SUBC (THIS VERSION) AND FULL C89
o The following keywords are not recognized:
const, double, float, goto, long, short, signed, typedef,
unsigned.
o There are only two primitive data types: the signed int and
the unsigned char; there are also void pointers, and there
is limited support for int(*)() (pointers to functions
of type int).
o No more than two levels of indirection are supported, and
arrays are limited to one dimension, i.e. valid declarators
are limited to x, x[], *x, *x[], **x (and (*x)()).
o K&R-style function declarations (with parameter
declarations between the parameter list and function body)
are not accepted.
o There are no ``const'' variables.
o There is no typedef.
o There are no unsigned integers, long integers, or signed
chars.
o Struct/union declarations must be separate from the
declarations of struct/union objects, i.e.
``struct p { int x, y; } q;'' will not work.
o Struct/union declarations must be global (struct and union
objects may be declared locally, though).
o There is no support for bit fields.
o Only ints, chars and arrays of int and char can be
initialized in their declarations; pointers can be
initialized with 0 (but not with NULL).
o Local arrays cannot have initializers.
o Local declarations are limited to the beginnings of function
bodies (they do not work in other compound statements).
o Arguments of prototypes must be named.
o There is no goto.
o There are no parameterized macros.
o The #if and #elif preprocessor commands are not recognized.
o The preprocessor does not accept multi-line commands.
o The preprocessor does not accept comments in (some) commands.
o The preprocessor does not recognize the # and ## operators.
o There may not be any blanks between the # that introduces
a preprocessor command and the subsequent command (e.g.:
"# define" would not be recognized as a valid command).
o The sizeof operator requires parentheses.
o Subscripting an integer with a pointer (e.g. 1["foo"]) is
not supported.
o Function pointers are limited to one single type, int(*)(),
and they have no argument types.
o There is no assert() due to the lack of parameterized macros.
o The atexit() mechanism is limited to one function (this may
even be covered by TCPL2).
o The signal() function returns int due to the lack of a more
sophisticated type system; the return value must be casted to
int(*)() manually.
o Most of the time-related functions are missing, in particular:
asctime(), gmtime(), localtime(), mktime(), and strftime().
o The clock() function is missing, because CLOCKS_PER_SEC
varies among systems.
o The ctime() function ignores the time zone.
o The varargs mechanism is slightly incompatible.
SELECTING A TARGET PLATFORM
The easiest way to prepare a build is to run the configure
script in this directory. Don't worry, it is just a simple
script that will figure out the host platform via uname and
link a few machine-dependent files into place.
If you want to configure the compiler manually: select one of
the target descriptions (cg*.c) files in src/targets/cg and
symlink it to src/cg.c. Also link the corresponding header
file into place:
(cd src && ln -fs targets/cg/cg386.c cg.c)
(cd src && ln -fs targets/cg/cg386.h cg.h)
Next select the C startup (crt0) file for your OS and CPU type
from src/targets/OS-CPU/ and link it to src/lib/crt0.s, e.g.:
(cd src/lib && \
ln -fs ../targets/freebsd-386/crt0-freebsd-386.s \
crt0.s)
If your OS/CPU combination is not supported, you might try
to port the compiler. See the file "Porting" for details.
You will also need some operating system-dependent
definitions, which are kept in files named "sys-OS-CPU.h"
in src/targets/OS-CPU/. Just symlink the appropriate file
to src/sys.h:
(cd src && \
ln -fs targets/freebsd-386/sys-freebsd-386.h sys.h)
Finally, select a limits-*.h file from targets/include/ that
reflects the machine word size of your target and link it to
src/include/limits.h:
(cd src/include && \
ln -fs ../targets/include/limits-32.h limits.h)
COMPILING THE COMPILER
The compiler sources are contained in the "src" directory,
so all the subsequent steps assume that this is your current
working directory. (I.e. do a "cd src" now.)
On a supported system, just type "make".
Without "make" the compiler can be bootstrapped by running:
cc -o scc0 *.c
To compile and package the runtime library:
./scc0 -c lib/*.c
ar -rc lib/libscc.a lib/*.o
ranlib lib/libscc.a
To compile the startup module:
as -o lib/crt0.o lib/crt0.s
To test the compiler, either run "make test" or perform the
following steps:
./scc0 -o scc1 *.c
./scc1 -o scc *.c
cmp scc1 scc
There should not be any differences between the scc1 and scc
executables.
INSTALLING THE COMPILER
The easy way would be to set up the PREFIX (and optionally
SCCDIR and BINDIR) variables in src/Makefile to suit your
taste and then run
make dirs # to create the directories
make install
If you want to install the SubC compiler manually, you will
have to change the SCCDIR variable in the compiler itself.
It points to the base directory which will contain the SubC
headers and runtime library. SCCDIR defaults to "." but can
be overridden on the command line:
./scc1 -o scc -D 'SCCDIR="INSTALLDIR"' *.c
(where INSTALLDIR is where the compiler will be installed.)
You can place the 'scc' executable wherever you want, as long
as its location is covered by the PATH environment variable.
The headers (include/*) go to INSTALLDIR/include, the library
'lib/libscc.a' and the startup module 'lib/crt0.o' go to
INSTALLDIR/lib.
To test the installation just re-compile the compiler:
rm scc && scc -o scc *.c
DOS SUPPORT
Please see the file SubC-for-DOS.
WINDOWS SUPPORT
There is a build script (winbuild.bat) in the base directory
of the package, but I have never tried it. Caveat utilitor!
All Windows-related code in the runtime system has been
generously supplied by Jean-Marc Lienher (http://cod5.org).
I am afraid I am not able to answer any questions about it,
because I know nothing about Windows.
The Windows version of SubC requires the MinGW infrastructure,
but, like the Linux version, does not use the GNU libc. To
compile SubC on Windows, just run configure and make, like
on a Unix system.
In case you have to configure it manually, you also have to
do the following:
Replace or symlink the following files:
ln -fs targets/lib/init-windows.c lib/init.c
ln -fs targets/lib/system-windows.c lib/system.c
Finally change the EXESFX (executable suffix) variable in
src/Makefile to ".exe" (without quotes).
After installing these changes, the compiler should bootstrap
as usual and pass the triple test.
THANKS
To the Super Dimension Fortress (SDF.ORG) for providing
free shell accounts on 64-bit NetBSD machines.
To Bakul Shah for granting me remote access to a 64-bit
FreeBSD system and a Linux VM.
To "minux" for porting the runtime module to Linux/x86-64.
To Jean-Marc Lienher (cod5.org) for porting the runtime module
to MinGW Windows/386.
To Romain LWPB for porting the runtime module to OpenBSD/386
and Darwin/x86-64 as well as for modifying the x86-64 code
generator to emit proper code for Darwin.
To The Unknown Hacker for various minor and not so minor
contributions.
CONTACT
Send feedback, suggestions, etc to:
n m h @ t 3 x . o r g
See http://t3x.org/contact.html for current ways through my
spam filter.