Tiny C Compiler Reference Documentation

Table of Contents

1. Introduction

TinyCC (aka TCC) is a small but hyper fast C compiler. Unlike other C compilers, it is meant to be self-relying: you do not need an external assembler or linker because TCC does that for you.

TCC compiles so fast that even for big projects Makefiles may not be necessary.

TCC not only supports ANSI C, but also most of the new ISO C99 standard and many GNUC extensions including inline assembly.

TCC can also be used to make C scripts, i.e. pieces of C source that you run as a Perl or Python script. Compilation is so fast that your script will be as fast as if it was an executable.

TCC can also automatically generate memory and bound checks (see section 6. TinyCC Memory and Bound checks) while allowing all C pointers operations. TCC can do these checks even if non patched libraries are used.

With libtcc, you can use TCC as a backend for dynamic code generation (see section 7. The libtcc library).

TCC mainly supports the i386 target on Linux and Windows. There are alpha ports for the ARM (arm-tcc) and the TMS320C67xx targets (c67-tcc). More information about the ARM port is available at http://lists.gnu.org/archive/html/tinycc-devel/2003-10/msg00044.html.

For usage on Windows, see also tcc-win32.txt.

2. Command line invocation

2.1 Quick start

usage: tcc [options] [infile1 infile2...] [`-run' infile args...]

TCC options are a very much like gcc options. The main difference is that TCC can also execute directly the resulting program and give it runtime arguments.

Here are some examples to understand the logic:

`tcc -run a.c'
Compile `a.c' and execute it directly
`tcc -run a.c arg1'
Compile a.c and execute it directly. arg1 is given as first argument to the main() of a.c.
`tcc a.c -run b.c arg1'
Compile `a.c' and `b.c', link them together and execute them. arg1 is given as first argument to the main() of the resulting program.
`tcc -o myprog a.c b.c'
Compile `a.c' and `b.c', link them and generate the executable `myprog'.
`tcc -o myprog a.o b.o'
link `a.o' and `b.o' together and generate the executable `myprog'.
`tcc -c a.c'
Compile `a.c' and generate object file `a.o'.
`tcc -c asmfile.S'
Preprocess with C preprocess and assemble `asmfile.S' and generate object file `asmfile.o'.
`tcc -c asmfile.s'
Assemble (but not preprocess) `asmfile.s' and generate object file `asmfile.o'.
`tcc -r -o ab.o a.c b.c'
Compile `a.c' and `b.c', link them together and generate the object file `ab.o'.


TCC can be invoked from scripts, just as shell scripts. You just need to add #!/usr/local/bin/tcc -run at the start of your C source:

#!/usr/local/bin/tcc -run
#include <stdio.h>

int main() 
    printf("Hello World\n");
    return 0;

TCC can read C source code from standard input when `-' is used in place of `infile'. Example:

echo 'main(){puts("hello");}' | tcc -run -

2.2 Option summary

General Options:

Display current TCC version, increase verbosity.
Generate an object file (`-o' option must also be given).
`-o outfile'
Put object file, executable, or dll into output file `outfile'.
Set the path where the tcc internal libraries can be found (default is `PREFIX/lib/tcc').
Output compilation statistics.
`-run source [args...]'
Compile file source and run it with the command line arguments args. In order to be able to give more than one argument to a script, several TCC options can be given after the `-run' option, separated by spaces. Example:
tcc "-run -L/usr/X11R6/lib -lX11" ex4.c
In a script, it gives the following header:
#!/usr/local/bin/tcc -run -L/usr/X11R6/lib -lX11
#include <stdlib.h>
int main(int argc, char **argv)

Preprocessor options:

Specify an additional include path. Include paths are searched in the order they are specified. System include paths are always searched after. The default system include paths are: `/usr/local/include', `/usr/include' and `PREFIX/lib/tcc/include'. (`PREFIX' is usually `/usr' or `/usr/local').
Define preprocessor symbol `sym' to val. If val is not present, its value is `1'. Function-like macros can also be defined: `-DF(a)=a+1'
Undefine preprocessor symbol `sym'.

Compilation flags:

Note: each of the following warning options has a negative form beginning with `-fno-'.

Let the char type be unsigned.
Let the char type be signed.
Do not generate common symbols for uninitialized data.
Add a leading underscore at the beginning of each C symbol.

Warning options:

Disable all warnings.

Note: each of the following warning options has a negative form beginning with `-Wno-'.

Warn about implicit function declaration.
Warn about unsupported GCC features that are ignored by TCC.
Make string constants be of type const char * instead of char *.
Abort compilation if warnings are issued.
Activate all warnings, except `-Werror', `-Wunusupported' and `-Wwrite-strings'.

Linker options:

Specify an additional static library path for the `-l' option. The default library paths are `/usr/local/lib', `/usr/lib' and `/lib'.
Link your program with dynamic library libxxx.so or static library libxxx.a. The library is searched in the paths specified by the `-L' option.
Generate a shared library instead of an executable (`-o' option must also be given).
Generate a statically linked executable (default is a shared linked executable) (`-o' option must also be given).
Export global symbols to the dynamic linker. It is useful when a library opened with dlopen() needs to access executable symbols.
Generate an object file combining all input files (`-o' option must also be given).
Set the start of the .text section to address.
Use fmt as output format. The supported output formats are:
ELF output format (default)
Binary image (only for executable output)
COFF output format (only for executable output for TMS320C67xx target)

Debugger options:

Generate run time debug information so that you get clear run time error messages: test.c:68: in function 'test5()': dereferencing invalid pointer instead of the laconic Segmentation fault.
Generate additional support code to check memory allocations and array/pointer bounds. `-g' is implied. Note that the generated code is slower and bigger in this case.
`-bt N'
Display N callers in stack traces. This is useful with `-g' or `-b'.

Note: GCC options `-Ox', `-fx' and `-mx' are ignored.

3. C language support

3.1 ANSI C

TCC implements all the ANSI C standard, including structure bit fields and floating point numbers (long double, double, and float fully supported).

3.2 ISOC99 extensions

TCC implements many features of the new C standard: ISO C99. Currently missing items are: complex and imaginary numbers and variable length arrays.

Currently implemented ISOC99 features:

3.3 GNU C extensions

TCC implements some GNU C extensions:

3.4 TinyCC extensions

4. TinyCC Assembler

Since version 0.9.16, TinyCC integrates its own assembler. TinyCC assembler supports a gas-like syntax (GNU assembler). You can desactivate assembler support if you want a smaller TinyCC executable (the C compiler does not rely on the assembler).

TinyCC Assembler is used to handle files with `.S' (C preprocessed assembler) and `.s' extensions. It is also used to handle the GNU inline assembler with the asm keyword.

4.1 Syntax

TinyCC Assembler supports most of the gas syntax. The tokens are the same as C.

4.2 Expressions

4.3 Labels

4.4 Directives

All directives are preceeded by a '.'. The following directives are supported:

4.5 X86 Assembler

All X86 opcodes are supported. Only ATT syntax is supported (source then destination operand order). If no size suffix is given, TinyCC tries to guess it from the operand sizes.

Currently, MMX opcodes are supported but not SSE ones.

5. TinyCC Linker

5.1 ELF file generation

TCC can directly output relocatable ELF files (object files), executable ELF files and dynamic ELF libraries without relying on an external linker.

Dynamic ELF libraries can be output but the C compiler does not generate position independent code (PIC). It means that the dynamic library code generated by TCC cannot be factorized among processes yet.

TCC linker eliminates unreferenced object code in libraries. A single pass is done on the object and library list, so the order in which object files and libraries are specified is important (same constraint as GNU ld). No grouping options (`--start-group' and `--end-group') are supported.

5.2 ELF file loader

TCC can load ELF object files, archives (.a files) and dynamic libraries (.so).

5.3 PE-i386 file generation

TCC for Windows supports the native Win32 executable file format (PE-i386). It generates EXE files (console and gui) and DLL files.

For usage on Windows, see also tcc-win32.txt.

5.4 GNU Linker Scripts

Because on many Linux systems some dynamic libraries (such as `/usr/lib/libc.so') are in fact GNU ld link scripts (horrible!), the TCC linker also supports a subset of GNU ld scripts.

The GROUP and FILE commands are supported. OUTPUT_FORMAT and TARGET are ignored.

Example from `/usr/lib/libc.so':

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a )

6. TinyCC Memory and Bound checks

This feature is activated with the `-b' (see section 2. Command line invocation).

Note that pointer size is unchanged and that code generated with bound checks is fully compatible with unchecked code. When a pointer comes from unchecked code, it is assumed to be valid. Even very obscure C code with casts should work correctly.

For more information about the ideas behind this method, see http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html.

Here are some examples of caught errors:

Invalid range with standard string function:
    char tab[10];
    memset(tab, 0, 11);
Out of bounds-error in global or local arrays:
    int tab[10];
    for(i=0;i<11;i++) {
        sum += tab[i];
Out of bounds-error in malloc'ed data:
    int *tab;
    tab = malloc(20 * sizeof(int));
    for(i=0;i<21;i++) {
        sum += tab4[i];
Access of freed memory:
    int *tab;
    tab = malloc(20 * sizeof(int));
    for(i=0;i<20;i++) {
        sum += tab4[i];
Double free:
    int *tab;
    tab = malloc(20 * sizeof(int));

7. The libtcc library

The libtcc library enables you to use TCC as a backend for dynamic code generation.

Read the `libtcc.h' to have an overview of the API. Read `libtcc_test.c' to have a very simple example.

The idea consists in giving a C string containing the program you want to compile directly to libtcc. Then you can access to any global symbol (function or variable) defined.

8. Developer's guide

This chapter gives some hints to understand how TCC works. You can skip it if you do not intend to modify the TCC code.

8.1 File reading

The BufferedFile structure contains the context needed to read a file, including the current line number. tcc_open() opens a new file and tcc_close() closes it. inp() returns the next character.

8.2 Lexer

next() reads the next token in the current file. next_nomacro() reads the next token without macro expansion.

tok contains the current token (see TOK_xxx) constants. Identifiers and keywords are also keywords. tokc contains additional infos about the token (for example a constant value if number or string token).

8.3 Parser

The parser is hardcoded (yacc is not necessary). It does only one pass, except:

8.4 Types

The types are stored in a single 'int' variable. It was choosen in the first stages of development when tcc was much simpler. Now, it may not be the best solution.

#define VT_INT        0  /* integer type */
#define VT_BYTE       1  /* signed byte type */
#define VT_SHORT      2  /* short type */
#define VT_VOID       3  /* void type */
#define VT_PTR        4  /* pointer */
#define VT_ENUM       5  /* enum definition */
#define VT_FUNC       6  /* function type */
#define VT_STRUCT     7  /* struct/union definition */
#define VT_FLOAT      8  /* IEEE float */
#define VT_DOUBLE     9  /* IEEE double */
#define VT_LDOUBLE   10  /* IEEE long double */
#define VT_BOOL      11  /* ISOC99 boolean type */
#define VT_LLONG     12  /* 64 bit integer */
#define VT_LONG      13  /* long integer (NEVER USED as type, only
                            during parsing) */
#define VT_BTYPE      0x000f /* mask for basic type */
#define VT_UNSIGNED   0x0010  /* unsigned type */
#define VT_ARRAY      0x0020  /* array type (also has VT_PTR) */
#define VT_BITFIELD   0x0040  /* bitfield modifier */

#define VT_STRUCT_SHIFT 16   /* structure/enum name shift (16 bits left) */

When a reference to another type is needed (for pointers, functions and structures), the 32 - VT_STRUCT_SHIFT high order bits are used to store an identifier reference.

The VT_UNSIGNED flag can be set for chars, shorts, ints and long longs.

Arrays are considered as pointers VT_PTR with the flag VT_ARRAY set.

The VT_BITFIELD flag can be set for chars, shorts, ints and long longs. If it is set, then the bitfield position is stored from bits VT_STRUCT_SHIFT to VT_STRUCT_SHIFT + 5 and the bit field size is stored from bits VT_STRUCT_SHIFT + 6 to VT_STRUCT_SHIFT + 11.

VT_LONG is never used except during parsing.

During parsing, the storage of an object is also stored in the type integer:

#define VT_EXTERN  0x00000080  /* extern definition */
#define VT_STATIC  0x00000100  /* static variable */
#define VT_TYPEDEF 0x00000200  /* typedef definition */

8.5 Symbols

All symbols are stored in hashed symbol stacks. Each symbol stack contains Sym structures.

Sym.v contains the symbol name (remember an idenfier is also a token, so a string is never necessary to store it). Sym.t gives the type of the symbol. Sym.r is usually the register in which the corresponding variable is stored. Sym.c is usually a constant associated to the symbol.

Four main symbol stacks are defined:

for the macros (#defines).
for the global variables, functions and types.
for the local variables, functions and types.
for the local labels (for goto).
for GCC block local labels (see the __label__ keyword).

sym_push() is used to add a new symbol in the local symbol stack. If no local symbol stack is active, it is added in the global symbol stack.

sym_pop(st,b) pops symbols from the symbol stack st until the symbol b is on the top of stack. If b is NULL, the stack is emptied.

sym_find(v) return the symbol associated to the identifier v. The local stack is searched first from top to bottom, then the global stack.

8.6 Sections

The generated code and datas are written in sections. The structure Section contains all the necessary information for a given section. new_section() creates a new section. ELF file semantics is assumed for each section.

The following sections are predefined:

is the section containing the generated code. ind contains the current position in the code section.
contains initialized data
contains uninitialized data
are used when bound checking is activated
are used when debugging is actived to store debug information
contain the exported symbols (currently only used for debugging).

8.7 Code generation

8.7.1 Introduction

The TCC code generator directly generates linked binary code in one pass. It is rather unusual these days (see gcc for example which generates text assembly), but it can be very fast and surprisingly little complicated.

The TCC code generator is register based. Optimization is only done at the expression level. No intermediate representation of expression is kept except the current values stored in the value stack.

On x86, three temporary registers are used. When more registers are needed, one register is spilled into a new temporary variable on the stack.

8.7.2 The value stack

When an expression is parsed, its value is pushed on the value stack (vstack). The top of the value stack is vtop. Each value stack entry is the structure SValue.

SValue.t is the type. SValue.r indicates how the value is currently stored in the generated code. It is usually a CPU register index (REG_xxx constants), but additional values and flags are defined:

#define VT_CONST     0x00f0
#define VT_LLOCAL    0x00f1
#define VT_LOCAL     0x00f2
#define VT_CMP       0x00f3
#define VT_JMP       0x00f4
#define VT_JMPI      0x00f5
#define VT_LVAL      0x0100
#define VT_SYM       0x0200
#define VT_MUSTCAST  0x0400
#define VT_MUSTBOUND 0x0800
#define VT_BOUNDED   0x8000
#define VT_LVAL_BYTE     0x1000
#define VT_LVAL_SHORT    0x2000
#define VT_LVAL_UNSIGNED 0x4000
indicates that the value is a constant. It is stored in the union SValue.c, depending on its type.
indicates a local variable pointer at offset SValue.c.i in the stack.
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 SValue.c.i. If any code is generated which destroys the CPU flags, this value MUST be put in a normal register.
indicates that the value is the consequence of a conditional jump. For VT_JMP, it is 1 if the jump is taken, 0 otherwise. For VT_JMPI it is inverted. These values are used to compile the || and && logical operators. 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.
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. Understanding the use VT_LVAL is very important if you want to understand how TCC works.
if the lvalue has an integer type, then these flags give its real type. The type alone is not enough in case of cast optimisations.
is a saved lvalue on the stack. VT_LLOCAL should be eliminated ASAP because its semantics are rather complicated.
indicates that a cast to the value type must be performed if the value is used (lazy casting).
indicates that the symbol SValue.sym must be added to the constant.
are only used for optional bound checking.

8.7.3 Manipulating the value stack

vsetc() and vset() pushes a new value on the value stack. If the previous vtop was stored in a very unsafe place(for example in the CPU flags), then some code is generated to put the previous vtop in a safe storage.

vpop() pops vtop. In some cases, it also generates cleanup code (for example if stacked floating point registers are used as on x86).

The gv(rc) function generates code to evaluate vtop (the top value of the stack) into registers. rc selects in which register class the value should be put. gv() is the most important function of the code generator.

gv2() is the same as gv() but for the top two stack entries.

8.7.4 CPU dependent code generation

See the `i386-gen.c' file to have an example.

must generate the code needed to load a stack value into a register.
must generate the code needed to store a register into a stack value lvalue.
should generate a function call
should generate a function prolog/epilog.
must generate the binary integer operation 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.
same as gen_opi() for floating point operations. The two top entries of the stack are guaranted to contain floating point values of same types.
integer to floating point conversion.
floating point to integer conversion.
floating point to floating point of different size conversion.
are only used for bounds checking.

8.8 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.

Concept Index

Jump to: _ - a - b - c - d - e - f - g - i - j - l - m - o - p - q - r - s - t - u - v - w


  • __asm__
  • a

  • align directive
  • aligned attribute
  • ascii directive
  • asciz directive
  • assembler
  • assembler directives
  • assembly, inline
  • b

  • bound checks
  • bss directive
  • byte directive
  • c

  • caching processor flags
  • cdecl attribute
  • code generation
  • comparison operators
  • constant propagation
  • CPU dependent
  • d

  • data directive
  • directives, assembler
  • dllexport attribute
  • e

  • ELF
  • f

  • FILE, linker command
  • fill directive
  • flags, caching
  • g

  • gas
  • global directive
  • globl directive
  • GROUP, linker command
  • i

  • inline assembly
  • int directive
  • j

  • jump optimization
  • l

  • linker
  • linker scripts
  • long directive
  • m

  • memory checks
  • o

  • optimizations
  • org directive
  • OUTPUT_FORMAT, linker command
  • p

  • packed attribute
  • PE-i386
  • previous directive
  • q

  • quad directive
  • r

  • regparm attribute
  • s

  • scripts, linker
  • section attribute
  • section directive
  • short directive
  • skip directive
  • space directive
  • stdcall attribute
  • strength reduction
  • string directive
  • t

  • TARGET, linker command
  • text directive
  • u

  • unused attribute
  • v

  • value stack
  • value stack, introduction
  • w

  • word directive

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