Landon Curt Noll
f615bba21e
The commit 00ae59cd47 had a
mistake that introduces changes to Makefiles for 1996 thru 2020
that should not have been included.
This change reverses these intermediate changes until
the given year's Makefiles are ready.
Best abuse of the rules:
Fabrice Bellard
451 chemin du mas de Matour
34790 GRABELS
France
http://bellard.org
Judges' Comments:
To build:
make bellard
Try:
./bellard bellard.otccex.c
<JUDGES_COMMENTS>
Selected Author's Comments:
OTCC is an Obfuscated Tiny C Compiler for i386-linux. It generates
FAST! i386 32 bit code (no bytecode) and it is powerful enough to
compile itself. OTCC supports a strict subset of C. This subset is
compilable by a standard ANSI C compiler. OTCC compiles,
assembles, links and runs C code without the need of any other
program.
You can use it by typing:
./bellard bellard.c [args]...
or by giving the C source to its standard input.
'args' are given to the 'main' function of bellard.c (argv[0] is
bellard.c).
Examples:
- Sample compilation and execution:
./bellard bellard.otccex.c 10
- Self compilation:
./bellard bellard.c bellard.otccex.c 10
- Self compilation iterated...
./bellard bellard.c bellard.c bellard.otccex.c 10
An alternate syntax is to use it as a script interpreter: you can
put '#!/usr/local/bin/otcc' at the beginning of your C source if
you installed otcc at this place.
Supported C language subset (read joint example 'otccex.c' to have
an introduction to OTCC dialect):
- Expressions:
* binary operators, by decreasing priority order: '*' '/' '%',
'+' '-', '>>' '<<', '<' '<=' '>' '>=', '==' '!=', '&',
'^', '|', '=', '&&', '||'.
* '&&' and '||' have the same semantics as C : left to right
evaluation and early exit.
* Parenthesis are supported.
* Unary operators: '&', '*' (pointer indirection), '-'
(negation), '+', '!', '~', post fixed '++' and '--'.
* Pointer indirection ('*') only works with explicit cast to
'char *', 'int *' or 'int (*)()' (function pointer).
* '++', '--', and unary '&' can only be used with variable
lvalue (left value).
* '=' can only be used with variable or '*' (pointer
indirection) lvalue.
* Function calls are supported with standard i386 calling
convention. Function pointers are supported with explicit
cast. Functions can be used before being declared.
- Types: only signed integer ('int') variables and functions can
be declared. Variables cannot be initialized in
declarations. Only old K&R function declarations are parsed
(implicit integer return value and no types on arguments).
- Any function or variable from the libc can be used because OTCC
uses the libc dynamic linker to resolve undefined symbols.
- Instructions: blocks ('{' '}') are supported as in C. 'if' and
'else' can be used for tests. The 'while' and 'for' C constructs
are supported for loops. 'break' can be used to exit
loops. 'return' is used for the return value of a function.
- Identifiers are parsed the same way as C. Local variables are
handled, but there is no local name space (not a problem if
different names are used for local and global variables).
- Numbers can be entered in decimal, hexadecimal ('0x' or '0X'
prefix), or octal ('0' prefix).
- '#define' is supported without function like arguments. No macro
recursion is tolerated. Other preprocessor directives are
ignored.
- C Strings and C character constants are supported. Only '\n',
'\"', '\'' and '\\' escapes are recognized.
- C Comments can be used (but no C++ comments).
- No error is displayed if an incorrect program is given.
- Memory: the code, data, and symbol sizes are limited to 100KB
(it can be changed in the source code).
Obfuscation:
No special effort was needed because obfuscation is almost
unavoidable for such a program :-) Defines must be used to
compress the code, and integrated i386 code generator leads to non
obvious code.
Portability:
OTCC only works on i386 linux because it generates i386 code. OTCC
also relies on little endianness, unaligned memory accesses and
ASCII representation of characters. It also supposes that no valid
pointers are less than 512. If all those constraints are met, then
OTCC could be theoretically used to "cross compile", although no
such support is currently integrated.
It was successfully compiled with gcc version 2.95.2. You get some
warnings because old K&R protos are used, some casts are implicit
and some functions are used before being defined. OTCC uses the
dynamic linker to resolve symbols with 'dlsym()', so '-ldl' must
be used as library when you compile it.