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https://github.com/frida/tinycc
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815 lines
23 KiB
Plaintext
815 lines
23 KiB
Plaintext
\input texinfo @c -*- texinfo -*-
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@settitle Tiny C Compiler Reference Documentation
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@titlepage
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@sp 7
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@center @titlefont{Tiny C Compiler Reference Documentation}
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@sp 3
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@end titlepage
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@chapter Introduction
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TinyCC (aka TCC) is a small but hyper fast C compiler. Unlike other C
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compilers, it is meant to be self-suffisant: you do not need an
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external assembler or linker because TCC does that for you.
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TCC compiles so @emph{fast} that even for big projects @code{Makefile}s may
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not be necessary.
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TCC not only supports ANSI C, but also most of the new ISO C99
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standard and many GNUC extensions.
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TCC can also be used to make @emph{C scripts}, i.e. pieces of C source
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that you run as a Perl or Python script. Compilation is so fast that
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your script will be as fast as if it was an executable.
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TCC can also automatically generate memory and bound checks
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(@xref{bounds}) while allowing all C pointers operations. TCC can do
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these checks even if non patched libraries are used.
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With @code{libtcc}, you can use TCC as a backend for dynamic code
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generation (@xref{libtcc}).
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@node invoke
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@chapter Command line invocation
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@section Quick start
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@example
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usage: tcc [-c] [-o outfile] [-Bdir] [-bench] [-Idir] [-Dsym[=val]] [-Usym]
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[-g] [-b] [-Ldir] [-llib] [-shared] [-static]
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[--] infile1 [infile2... --] [infile_args...]
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@end example
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TCC options are a very much like gcc. The main difference is that TCC
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can also execute directly the resulting program and give it runtime
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arguments.
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Here are some examples to understand the logic:
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@table @code
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@item tcc a.c
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Compile a.c and execute it directly
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@item tcc a.c arg1
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Compile a.c and execute it directly. arg1 is given as first argument to
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the @code{main()} of a.c.
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@item tcc -- a.c b.c -- arg1
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Compile a.c and b.c, link them together and execute them. arg1 is given
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as first argument to the @code{main()} of the resulting program. Because
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multiple C files are specified, @code{--} are necessary to clearly separate the
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program arguments from the TCC options.
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@item tcc -o myprog a.c b.c
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Compile a.c and b.c, link them and generate the executable myprog.
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@item tcc -o myprog a.o b.o
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link a.o and b.o together and generate the executable myprog.
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@item tcc -c a.c
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Compile a.c and generate object file a.o
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@item tcc -r -o ab.o a.c b.c
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Compile a.c and b.c, link them together and generate the object file ab.o.
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@end table
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Scripting:
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TCC can be invoked from @emph{scripts}, just as shell scripts. You just
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need to add @code{#!/usr/local/bin/tcc} at the start of your C source:
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@example
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#!/usr/local/bin/tcc
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#include <stdio.h>
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int main()
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{
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printf("Hello World\n");
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return 0;
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}
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@end example
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@section Option summary
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General Options:
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@table @samp
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@item -c
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Generate an object file (@samp{-o} option must also be given).
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@item -o outfile
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Put object file, executable, or dll into output file @file{outfile}.
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@item -Bdir
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Set the path where the tcc internal libraries can be found (default is
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@file{PREFIX/lib/tcc}).
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@item -bench
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Output compilation statistics.
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@end table
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Preprocessor options:
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@table @samp
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@item -Idir
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Specify an additionnal include path. Include paths are searched in the
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order they are specified.
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System include paths are always searched after. The default system
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include paths are: @file{/usr/local/include}, @file{/usr/include}
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and @file{PREFIX/lib/tcc/include}. (@code{PREFIX} is usually
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@file{/usr} or @file{/usr/local}).
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@item -Dsym[=val]
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Define preprocessor symbol 'sym' to
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val. If val is not present, its value is '1'. Function-like macros can
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also be defined: @code{'-DF(a)=a+1'}
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@item -Usym
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Undefine preprocessor symbol 'sym'.
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@end table
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C compiler options:
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@table @samp
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@item -g
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Generate run time debug information so that you get clear run time
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error messages: @code{ test.c:68: in function 'test5()': dereferencing
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invalid pointer} instead of the laconic @code{Segmentation
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fault}.
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@item -b
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Generate additionnal support code to check
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memory allocations and array/pointer bounds. '-g' is implied. Note
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that the generated code is slower and bigger in this case.
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@end table
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Linker options:
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@table @samp
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@item -Ldir
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Specify an additionnal static library path for the @samp{-l} option. The
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default library paths are @file{/usr/local/lib}, @file{/usr/lib} and @file{/lib}.
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@item -lxxx
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Link your program with dynamic library libxxx.so or static library
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libxxx.a. The library is searched in the paths specified by the
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@samp{-L} option.
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@item -shared
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Generate a shared library instead of an executable (@samp{-o} option
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must also be given).
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@item -static
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Generate a statically linked executable (default is a shared linked
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executable) (@samp{-o} option must also be given).
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@item -r
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Generate an object file combining all input files (@samp{-o} option must
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also be given).
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@end table
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@chapter C language support
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@section ANSI C
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TCC implements all the ANSI C standard, including structure bit fields
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and floating point numbers (@code{long double}, @code{double}, and
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@code{float} fully supported). The following limitations are known:
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@itemize
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@item The preprocessor tokens are the same as C. It means that in some
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rare cases, preprocessed numbers are not handled exactly as in ANSI
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C. This approach has the advantage of being simpler and FAST!
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@end itemize
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@section ISOC99 extensions
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TCC implements many features of the new C standard: ISO C99. Currently
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missing items are: complex and imaginary numbers and variable length
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arrays.
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Currently implemented ISOC99 features:
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@itemize
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@item 64 bit @code{'long long'} types are fully supported.
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@item The boolean type @code{'_Bool'} is supported.
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@item @code{'__func__'} is a string variable containing the current
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function name.
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@item Variadic macros: @code{__VA_ARGS__} can be used for
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function-like macros:
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@example
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#define dprintf(level, __VA_ARGS__) printf(__VA_ARGS__)
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@end example
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@code{dprintf} can then be used with a variable number of parameters.
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@item Declarations can appear anywhere in a block (as in C++).
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@item Array and struct/union elements can be initialized in any order by
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using designators:
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@example
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struct { int x, y; } st[10] = { [0].x = 1, [0].y = 2 };
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int tab[10] = { 1, 2, [5] = 5, [9] = 9};
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@end example
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@item Compound initializers are supported:
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@example
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int *p = (int []){ 1, 2, 3 };
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@end example
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to initialize a pointer pointing to an initialized array. The same
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works for structures and strings.
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@item Hexadecimal floating point constants are supported:
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@example
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double d = 0x1234p10;
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@end example
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is the same as writing
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@example
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double d = 4771840.0;
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@end example
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@item @code{'inline'} keyword is ignored.
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@item @code{'restrict'} keyword is ignored.
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@end itemize
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@section GNU C extensions
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TCC implements some GNU C extensions:
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@itemize
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@item array designators can be used without '=':
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@example
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int a[10] = { [0] 1, [5] 2, 3, 4 };
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@end example
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@item Structure field designators can be a label:
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@example
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struct { int x, y; } st = { x: 1, y: 1};
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@end example
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instead of
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@example
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struct { int x, y; } st = { .x = 1, .y = 1};
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@end example
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@item @code{'\e'} is ASCII character 27.
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@item case ranges : ranges can be used in @code{case}s:
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@example
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switch(a) {
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case 1 ... 9:
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printf("range 1 to 9\n");
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break;
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default:
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printf("unexpected\n");
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break;
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}
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@end example
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@item The keyword @code{__attribute__} is handled to specify variable or
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function attributes. The following attributes are supported:
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@itemize
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@item @code{aligned(n)}: align data to n bytes (must be a power of two).
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@item @code{section(name)}: generate function or data in assembly
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section name (name is a string containing the section name) instead
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of the default section.
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@item @code{unused}: specify that the variable or the function is unused.
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@item @code{cdecl}: use standard C calling convention.
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@item @code{stdcall}: use Pascal-like calling convention.
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@end itemize
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Here are some examples:
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@example
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int a __attribute__ ((aligned(8), section(".mysection")));
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@end example
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align variable @code{'a'} to 8 bytes and put it in section @code{.mysection}.
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@example
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int my_add(int a, int b) __attribute__ ((section(".mycodesection")))
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{
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return a + b;
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}
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@end example
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generate function @code{'my_add'} in section @code{.mycodesection}.
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@item GNU style variadic macros:
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@example
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#define dprintf(fmt, args...) printf(fmt, ## args)
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dprintf("no arg\n");
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dprintf("one arg %d\n", 1);
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@end example
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@item @code{__FUNCTION__} is interpreted as C99 @code{__func__}
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(so it has not exactly the same semantics as string literal GNUC
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where it is a string literal).
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@end itemize
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@section TinyCC extensions
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@itemize
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@item @code{__TINYC__} is a predefined macro to @code{'1'} to
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indicate that you use TCC.
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@item @code{'#!'} at the start of a line is ignored to allow scripting.
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@item Binary digits can be entered (@code{'0b101'} instead of
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@code{'5'}).
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@item @code{__BOUNDS_CHECKING_ON} is defined if bound checking is activated.
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@end itemize
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@chapter TinyCC Linker
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@section ELF file generation
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TCC can directly output relocatable ELF files (object files),
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executable ELF files and dynamic ELF libraries without relying on an
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external linker.
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Dynamic ELF libraries can be output but the C compiler does not generate
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position independant code (PIC) code. It means that the dynamic librairy
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code generated by TCC cannot be factorized among processes yet.
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TCC linker cannot currently suppress unused object code. But TCC
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will soon integrate a novel feature not found in GNU tools: unused code
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will be suppressed at the function or variable level, provided you only
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use TCC to compile your files.
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@section ELF file loader
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TCC can load ELF object files, archives (.a files) and dynamic
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libraries (.so).
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@section GNU Linker Scripts
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Because on many Linux systems some dynamic libraries (such as
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@file{/usr/lib/libc.so}) are in fact GNU ld link scripts (horrible!),
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TCC linker also support a subset of GNU ld scripts.
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The @code{GROUP} and @code{FILE} commands are supported.
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Example from @file{/usr/lib/libc.so}:
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@example
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/* GNU ld script
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Use the shared library, but some functions are only in
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the static library, so try that secondarily. */
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GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a )
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@end example
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@node bounds
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@chapter TinyCC Memory and Bound checks
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This feature is activated with the @code{'-b'} (@xref{invoke}).
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Note that pointer size is @emph{unchanged} and that code generated
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with bound checks is @emph{fully compatible} with unchecked
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code. When a pointer comes from unchecked code, it is assumed to be
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valid. Even very obscure C code with casts should work correctly.
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To have more information about the ideas behind this method, check at
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@url{http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html}.
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Here are some examples of catched errors:
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@table @asis
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@item Invalid range with standard string function:
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@example
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{
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char tab[10];
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memset(tab, 0, 11);
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}
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@end example
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@item Bound error in global or local arrays:
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@example
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{
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int tab[10];
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for(i=0;i<11;i++) {
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sum += tab[i];
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}
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}
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@end example
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@item Bound error in allocated data:
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@example
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{
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int *tab;
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tab = malloc(20 * sizeof(int));
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for(i=0;i<21;i++) {
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sum += tab4[i];
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}
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free(tab);
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}
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@end example
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@item Access to a freed region:
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@example
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{
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int *tab;
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tab = malloc(20 * sizeof(int));
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free(tab);
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for(i=0;i<20;i++) {
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sum += tab4[i];
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}
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}
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@end example
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@item Freeing an already freed region:
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@example
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{
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int *tab;
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tab = malloc(20 * sizeof(int));
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free(tab);
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free(tab);
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}
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@end example
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@end table
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@node libtcc
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@chapter The @code{libtcc} library
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The @code{libtcc} library enables you to use TCC as a backend for
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dynamic code generation.
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Read the @file{libtcc.h} to have an overview of the API. Read
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@file{libtcc_test.c} to have a very simple example.
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The idea consists in giving a C string containing the program you want
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to compile directly to @code{libtcc}. Then the @code{main()} function of
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the compiled string can be launched.
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@chapter Developper's guide
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This chapter gives some hints to understand how TCC works. You can skip
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it if you do not intend to modify the TCC code.
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@section File reading
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The @code{BufferedFile} structure contains the context needed to read a
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file, including the current line number. @code{tcc_open()} opens a new
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file and @code{tcc_close()} closes it. @code{inp()} returns the next
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character.
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@section Lexer
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@code{next()} reads the next token in the current
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file. @code{next_nomacro()} reads the next token without macro
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expansion.
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@code{tok} contains the current token (see @code{TOK_xxx})
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constants. Identifiers and keywords are also keywords. @code{tokc}
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contains additionnal infos about the token (for example a constant value
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if number or string token).
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@section Parser
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The parser is hardcoded (yacc is not necessary). It does only one pass,
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except:
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@itemize
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@item For initialized arrays with unknown size, a first pass
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is done to count the number of elements.
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@item For architectures where arguments are evaluated in
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reverse order, a first pass is done to reverse the argument order.
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@end itemize
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@section Types
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The types are stored in a single 'int' variable. It was choosen in the
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first stages of development when tcc was much simpler. Now, it may not
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be the best solution.
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@example
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#define VT_INT 0 /* integer type */
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#define VT_BYTE 1 /* signed byte type */
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#define VT_SHORT 2 /* short type */
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#define VT_VOID 3 /* void type */
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#define VT_PTR 4 /* pointer */
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#define VT_ENUM 5 /* enum definition */
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#define VT_FUNC 6 /* function type */
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#define VT_STRUCT 7 /* struct/union definition */
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#define VT_FLOAT 8 /* IEEE float */
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#define VT_DOUBLE 9 /* IEEE double */
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#define VT_LDOUBLE 10 /* IEEE long double */
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#define VT_BOOL 11 /* ISOC99 boolean type */
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#define VT_LLONG 12 /* 64 bit integer */
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#define VT_LONG 13 /* long integer (NEVER USED as type, only
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during parsing) */
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#define VT_BTYPE 0x000f /* mask for basic type */
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#define VT_UNSIGNED 0x0010 /* unsigned type */
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#define VT_ARRAY 0x0020 /* array type (also has VT_PTR) */
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#define VT_BITFIELD 0x0040 /* bitfield modifier */
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#define VT_STRUCT_SHIFT 16 /* structure/enum name shift (16 bits left) */
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@end example
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When a reference to another type is needed (for pointers, functions and
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structures), the @code{32 - VT_STRUCT_SHIFT} high order bits are used to
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store an identifier reference.
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The @code{VT_UNSIGNED} flag can be set for chars, shorts, ints and long
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longs.
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Arrays are considered as pointers @code{VT_PTR} with the flag
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@code{VT_ARRAY} set.
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The @code{VT_BITFIELD} flag can be set for chars, shorts, ints and long
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longs. If it is set, then the bitfield position is stored from bits
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VT_STRUCT_SHIFT to VT_STRUCT_SHIFT + 5 and the bit field size is stored
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from bits VT_STRUCT_SHIFT + 6 to VT_STRUCT_SHIFT + 11.
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@code{VT_LONG} is never used except during parsing.
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During parsing, the storage of an object is also stored in the type
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integer:
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@example
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#define VT_EXTERN 0x00000080 /* extern definition */
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#define VT_STATIC 0x00000100 /* static variable */
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#define VT_TYPEDEF 0x00000200 /* typedef definition */
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@end example
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@section Symbols
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All symbols are stored in hashed symbol stacks. Each symbol stack
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contains @code{Sym} structures.
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@code{Sym.v} contains the symbol name (remember
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an idenfier is also a token, so a string is never necessary to store
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it). @code{Sym.t} gives the type of the symbol. @code{Sym.r} is usually
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the register in which the corresponding variable is stored. @code{Sym.c} is
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usually a constant associated to the symbol.
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Four main symbol stacks are defined:
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@table @code
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@item define_stack
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for the macros (@code{#define}s).
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@item global_stack
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for the global variables, functions and types.
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@item local_stack
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for the local variables, functions and types.
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@item label_stack
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for the local labels (for @code{goto}).
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@end table
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@code{sym_push()} is used to add a new symbol in the local symbol
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stack. If no local symbol stack is active, it is added in the global
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symbol stack.
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@code{sym_pop(st,b)} pops symbols from the symbol stack @var{st} until
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the symbol @var{b} is on the top of stack. If @var{b} is NULL, the stack
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is emptied.
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@code{sym_find(v)} return the symbol associated to the identifier
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@var{v}. The local stack is searched first from top to bottom, then the
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global stack.
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@section Sections
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The generated code and datas are written in sections. The structure
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@code{Section} contains all the necessary information for a given
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section. @code{new_section()} creates a new section. ELF file semantics
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is assumed for each section.
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The following sections are predefined:
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@table @code
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@item text_section
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is the section containing the generated code. @var{ind} contains the
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current position in the code section.
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@item data_section
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contains initialized data
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@item bss_section
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contains uninitialized data
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@item bounds_section
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@itemx lbounds_section
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are used when bound checking is activated
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@item stab_section
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@itemx stabstr_section
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are used when debugging is actived to store debug information
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@item symtab_section
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@itemx strtab_section
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contain the exported symbols (currently only used for debugging).
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@end table
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@section Code generation
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@subsection Introduction
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The TCC code generator directly generates linked binary code in one
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pass. It is rather unusual these days (see gcc for example which
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generates text assembly), but it allows to be very fast and surprisingly
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not so complicated.
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The TCC code generator is register based. Optimization is only done at
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the expression level. No intermediate representation of expression is
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kept except the current values stored in the @emph{value stack}.
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On x86, three temporary registers are used. When more registers are
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needed, one register is flushed in a new local variable.
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@subsection The value stack
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When an expression is parsed, its value is pushed on the value stack
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(@var{vstack}). The top of the value stack is @var{vtop}. Each value
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stack entry is the structure @code{SValue}.
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@code{SValue.t} is the type. @code{SValue.r} indicates how the value is
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currently stored in the generated code. It is usually a CPU register
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index (@code{REG_xxx} constants), but additionnal values and flags are
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defined:
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@example
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#define VT_CONST 0x00f0
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#define VT_LLOCAL 0x00f1
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#define VT_LOCAL 0x00f2
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#define VT_CMP 0x00f3
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#define VT_JMP 0x00f4
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#define VT_JMPI 0x00f5
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#define VT_LVAL 0x0100
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#define VT_SYM 0x0200
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#define VT_MUSTCAST 0x0400
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#define VT_MUSTBOUND 0x0800
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#define VT_BOUNDED 0x8000
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#define VT_LVAL_BYTE 0x1000
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#define VT_LVAL_SHORT 0x2000
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#define VT_LVAL_UNSIGNED 0x4000
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#define VT_LVAL_TYPE (VT_LVAL_BYTE | VT_LVAL_SHORT | VT_LVAL_UNSIGNED)
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@end example
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@table @code
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@item VT_CONST
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indicates that the value is a constant. It is stored in the union
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@code{SValue.c}, depending on its type.
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@item VT_LOCAL
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|
indicates a local variable pointer at offset @code{SValue.c.i} in the
|
|
stack.
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@item VT_CMP
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|
indicates that the value is actually stored in the CPU flags (i.e. the
|
|
value is the consequence of a test). The value is either 0 or 1. The
|
|
actual CPU flags used is indicated in @code{SValue.c.i}.
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If any code is generated which destroys the CPU flags, this value MUST be
|
|
put in a normal register.
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|
|
@item VT_JMP
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|
@itemx VT_JMPI
|
|
indicates that the value is the consequence of a jmp. For VT_JMP, it is
|
|
1 if the jump is taken, 0 otherwise. For VT_JMPI it is inverted.
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|
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These values are used to compile the @code{||} and @code{&&} logical
|
|
operators.
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If any code is generated, this value MUST be put in a normal
|
|
register. Otherwise, the generated code won't be executed if the jump is
|
|
taken.
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|
|
@item VT_LVAL
|
|
is a flag indicating that the value is actually an lvalue (left value of
|
|
an assignment). It means that the value stored is actually a pointer to
|
|
the wanted value.
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|
|
|
Understanding the use @code{VT_LVAL} is very important if you want to
|
|
understand how TCC works.
|
|
|
|
@item VT_LVAL_BYTE
|
|
@itemx VT_LVAL_SHORT
|
|
@itemx VT_LVAL_UNSIGNED
|
|
if the lvalue has an integer type, then these flags give its real
|
|
type. The type alone is not suffisant in case of cast optimisations.
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|
|
|
@item VT_LLOCAL
|
|
is a saved lvalue on the stack. @code{VT_LLOCAL} should be suppressed
|
|
ASAP because its semantics are rather complicated.
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|
|
@item VT_MUSTCAST
|
|
indicates that a cast to the value type must be performed if the value
|
|
is used (lazy casting).
|
|
|
|
@item VT_SYM
|
|
indicates that the symbol @code{SValue.sym} must be added to the constant.
|
|
|
|
@item VT_MUSTBOUND
|
|
@itemx VT_BOUNDED
|
|
are only used for optional bound checking.
|
|
|
|
@end table
|
|
|
|
@subsection Manipulating the value stack
|
|
|
|
@code{vsetc()} and @code{vset()} pushes a new value on the value
|
|
stack. If the previous @code{vtop} was stored in a very unsafe place(for
|
|
example in the CPU flags), then some code is generated to put the
|
|
previous @code{vtop} in a safe storage.
|
|
|
|
@code{vpop()} pops @code{vtop}. In some cases, it also generates cleanup
|
|
code (for example if stacked floating point registers are used as on
|
|
x86).
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|
|
|
The @code{gv(rc)} function generates code to evaluate @code{vtop} (the
|
|
top value of the stack) into registers. @var{rc} selects in which
|
|
register class the value should be put. @code{gv()} is the @emph{most
|
|
important function} of the code generator.
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|
|
|
@code{gv2()} is the same as @code{gv()} but for the top two stack
|
|
entries.
|
|
|
|
@subsection CPU dependent code generation
|
|
|
|
See the @file{i386-gen.c} file to have an example.
|
|
|
|
@table @code
|
|
|
|
@item load()
|
|
must generate the code needed to load a stack value into a register.
|
|
|
|
@item store()
|
|
must generate the code needed to store a register into a stack value
|
|
lvalue.
|
|
|
|
@item gfunc_start()
|
|
@itemx gfunc_param()
|
|
@itemx gfunc_call()
|
|
should generate a function call
|
|
|
|
@item gfunc_prolog()
|
|
@itemx gfunc_epilog()
|
|
should generate a function prolog/epilog.
|
|
|
|
@item gen_opi(op)
|
|
must generate the binary integer operation @var{op} on the two top
|
|
entries of the stack which are guaranted to contain integer types.
|
|
|
|
The result value should be put on the stack.
|
|
|
|
@item gen_opf(op)
|
|
same as @code{gen_opi()} for floating point operations. The two top
|
|
entries of the stack are guaranted to contain floating point values of
|
|
same types.
|
|
|
|
@item gen_cvt_itof()
|
|
integer to floating point conversion.
|
|
|
|
@item gen_cvt_ftoi()
|
|
floating point to integer conversion.
|
|
|
|
@item gen_cvt_ftof()
|
|
floating point to floating point of different size conversion.
|
|
|
|
@item gen_bounded_ptr_add()
|
|
@item gen_bounded_ptr_deref()
|
|
are only used for bound checking.
|
|
|
|
@end table
|
|
|
|
@section Optimizations done
|
|
|
|
Constant propagation is done for all operations. Multiplications and
|
|
divisions are optimized to shifts when appropriate. Comparison
|
|
operators are optimized by maintaining a special cache for the
|
|
processor flags. &&, || and ! are optimized by maintaining a special
|
|
'jump target' value. No other jump optimization is currently performed
|
|
because it would require to store the code in a more abstract fashion.
|
|
|