Tiny C Compiler Reference Documentation

Table of Contents

Tiny C Compiler Reference Documentation

This manual documents version 0.9.27 of the Tiny C Compiler.

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 Bounds) 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 Libtcc).

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:


Generate an object file.

-o outfile

Put object file, executable, or dll into output file outfile.

-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:

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

Display TCC version.


Show included files. As sole argument, print search dirs. -vvv shows tries too.


Display compilation statistics.

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’.


Preprocess only, to stdout or file (with -o).

Compilation flags:

Note: each of the following 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.


Allow a MS C compiler extensions to the language. Currently this assumes a nested named structure declaration without an identifier behaves like an unnamed one.


Allow dollar signs in identifiers

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 and LIBRARY_PATH variable.


Set the path where the tcc internal libraries (and include files) can be found (default is PREFIX/lib/tcc).


Generate a shared library instead of an executable.

-soname name

set name for shared library to be used at runtime


Generate a statically linked executable (default is a shared linked executable).


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.


Put custom search path for dynamic libraries into executable.


When putting a custom search path for dynamic libraries into the executable, create the new ELF dynamic tag DT_RUNPATH instead of the old legacy DT_RPATH.


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)


Set type for PE (Windows) executables.

-Wl,-[Ttext=# | section-alignment=# | file-alignment=# | image-base=# | stack=#]

Modify executable layout.




Turn on/off linking of all objects in archives.

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.

Note: -b is only available on i386 when using libtcc for the moment.

-bt N

Display N callers in stack traces. This is useful with -g or -b.

Misc options:


Generate makefile fragment with dependencies.

-MF depfile

Use depfile as output for -MD.


Print the configured installation directory and a list of library and include directories tcc will search.


Print version.

Target specific options:


Use an algorithm for bitfield alignment consistent with MSVC. Default is gcc’s algorithm.

-mfloat-abi (ARM only)

Select the float ABI. Possible values: softfp and hard


Do not use sse registers on x86_64

-m32, -m64

Pass command line to the i386/x86_64 cross compiler.

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

Environment variables that affect how tcc operates.


A colon-separated list of directories searched for include files, directories given with -I are searched first.


A colon-separated list of directories searched for libraries for the -l option, directories given with -L are searched first.

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.

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 deactivate 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 preceded 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 Invoke).

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 chosen 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_VLA        0x20000 /* VLA type (also has VT_PTR and VT_ARRAY) */
#define VT_BITFIELD   0x0040  /* bitfield modifier */
#define VT_CONSTANT   0x0800  /* const modifier */
#define VT_VOLATILE   0x1000  /* volatile modifier */
#define VT_DEFSIGN    0x2000  /* signed type */

#define VT_STRUCT_SHIFT 18   /* structure/enum name shift (14 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. Variable length arrays are considered as special arrays and have flag VT_VLA set instead of VT_ARRAY.

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 */
#define VT_INLINE  0x00000400  /* inline definition */
#define VT_IMPORT  0x00004000  /* win32: extern data imported from dll */
#define VT_EXPORT  0x00008000  /* win32: data exported from dll */
#define VT_WEAK    0x00010000  /* win32: data exported from dll */

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 identifier 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 like its address for normal symbols, and the number of entries for symbols representing arrays. Variable length array types use Sym.c as a location on the stack which holds the runtime sizeof for the type.

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 data 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 active 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_LVAL must also be set with VT_LLOCAL. VT_LLOCAL can arise when a VT_LVAL in a register has to be saved to the stack, or it can come from an architecture-specific calling convention.


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 guaranteed 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 guaranteed 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  
Index Entry  Section

__asm__: Clang

align directive: asm
aligned attribute: Clang
ascii directive: asm
asciz directive: asm
assembler: asm
assembler directives: asm
assembly, inline: Clang

bound checks: Bounds
bss directive: asm
byte directive: asm

caching processor flags: devel
cdecl attribute: Clang
code generation: devel
comparison operators: devel
constant propagation: devel
CPU dependent: devel

data directive: asm
directives, assembler: asm
dllexport attribute: Clang

ELF: linker

FILE, linker command: linker
fill directive: asm
flags, caching: devel

gas: Clang
global directive: asm
globl directive: asm
GROUP, linker command: linker

inline assembly: Clang
int directive: asm

jump optimization: devel

linker: linker
linker scripts: linker
long directive: asm

memory checks: Bounds

optimizations: devel
org directive: asm
OUTPUT_FORMAT, linker command: linker

packed attribute: Clang
PE-i386: linker
previous directive: asm

quad directive: asm

regparm attribute: Clang

scripts, linker: linker
section attribute: Clang
section directive: asm
short directive: asm
skip directive: asm
space directive: asm
stdcall attribute: Clang
strength reduction: devel
string directive: asm

TARGET, linker command: linker
text directive: asm

unused attribute: Clang

value stack: devel
value stack, introduction: devel

word directive: asm

Jump to:   _  
A   B   C   D   E   F   G   I   J   L   M   O   P   Q   R   S   T   U   V   W