\input texinfo @c -*- texinfo -*- @settitle Tiny C Compiler Reference Documentation @titlepage @sp 7 @center @titlefont{Tiny C Compiler Reference Documentation} @sp 3 @end titlepage @chapter Introduction TinyCC (aka TCC) is a small but hyper fast C compiler. Unlike other C compilers, it is meant to be self-suffisant: you do not need an external assembler or linker because TCC does that for you. TCC compiles so @emph{fast} that even for big projects @code{Makefile}s may not be necessary. TCC not only supports ANSI C, but also most of the new ISO C99 standard and many GNUC extensions. TCC can also be used to make @emph{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 (@xref{bounds}) while allowing all C pointers operations. TCC can do these checks even if non patched libraries are used. With @code{libtcc}, you can use TCC as a backend for dynamic code generation (@xref{libtcc}). @node invoke @chapter Command line invocation @example usage: tcc [-Idir] [-Dsym[=val]] [-Usym] [-llib] [-g] [-b] [-i infile] infile [infile_args...] @end example @table @samp @item -Idir Specify an additionnal include path. The default ones are: @file{/usr/include}, @code{prefix}@file{/lib/tcc/include} (@code{prefix} is usually @file{/usr} or @file{/usr/local}). @item -Dsym[=val] Define preprocessor symbol 'sym' to val. If val is not present, its value is '1'. Function-like macros can also be defined: @code{'-DF(a)=a+1'} @item -Usym Undefine preprocessor symbol 'sym'. @item -lxxx Dynamically link your program with library libxxx.so. Standard library paths are checked, including those specified with LD_LIBRARY_PATH. @item -g Generate run time debug information so that you get clear run time error messages: @code{ test.c:68: in function 'test5()': dereferencing invalid pointer} instead of the laconic @code{Segmentation fault}. @item -b Generate additionnal 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. @item -i file Compile C source 'file' before main C source. With this command, multiple C files can be compiled and linked together. @end table Note: the @code{-o file} option to generate an ELF executable is currently unsupported. @chapter C language support @section ANSI C TCC implements all the ANSI C standard, including structure bit fields and floating point numbers (@code{long double}, @code{double}, and @code{float} fully supported). The following limitations are known: @itemize @item The preprocessor tokens are the same as C. It means that in some rare cases, preprocessed numbers are not handled exactly as in ANSI C. This approach has the advantage of being simpler and FAST! @end itemize @section 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: @itemize @item 64 bit @code{'long long'} types are fully supported. @item The boolean type @code{'_Bool'} is supported. @item @code{'__func__'} is a string variable containing the current function name. @item Variadic macros: @code{__VA_ARGS__} can be used for function-like macros: @example #define dprintf(level, __VA_ARGS__) printf(__VA_ARGS__) @end example @code{dprintf} can then be used with a variable number of parameters. @item Declarations can appear anywhere in a block (as in C++). @item Array and struct/union elements can be initialized in any order by using designators: @example struct { int x, y; } st[10] = { [0].x = 1, [0].y = 2 }; int tab[10] = { 1, 2, [5] = 5, [9] = 9}; @end example @item Compound initializers are supported: @example int *p = (int []){ 1, 2, 3 }; @end example to initialize a pointer pointing to an initialized array. The same works for structures and strings. @item Hexadecimal floating point constants are supported: @example double d = 0x1234p10; @end example is the same as writing @example double d = 4771840.0; @end example @item @code{'inline'} keyword is ignored. @item @code{'restrict'} keyword is ignored. @end itemize @section GNU C extensions TCC implements some GNU C extensions: @itemize @item array designators can be used without '=': @example int a[10] = { [0] 1, [5] 2, 3, 4 }; @end example @item Structure field designators can be a label: @example struct { int x, y; } st = { x: 1, y: 1}; @end example instead of @example struct { int x, y; } st = { .x = 1, .y = 1}; @end example @item @code{'\e'} is ASCII character 27. @item case ranges : ranges can be used in @code{case}s: @example switch(a) { case 1 ... 9: printf("range 1 to 9\n"); break; default: printf("unexpected\n"); break; } @end example @item The keyword @code{__attribute__} is handled to specify variable or function attributes. The following attributes are supported: @itemize @item @code{aligned(n)}: align data to n bytes (must be a power of two). @item @code{section(name)}: generate function or data in assembly section name (name is a string containing the section name) instead of the default section. @item @code{unused}: specify that the variable or the function is unused. @item @code{cdecl}: use standard C calling convention. @item @code{stdcall}: use Pascal-like calling convention. @end itemize Here are some examples: @example int a __attribute__ ((aligned(8), section(".mysection"))); @end example align variable @code{'a'} to 8 bytes and put it in section @code{.mysection}. @example int my_add(int a, int b) __attribute__ ((section(".mycodesection"))) { return a + b; } @end example generate function @code{'my_add'} in section @code{.mycodesection}. @item GNU style variadic macros: @example #define dprintf(fmt, args...) printf(fmt, ## args) dprintf("no arg\n"); dprintf("one arg %d\n", 1); @end example @end itemize @section TinyCC extensions @itemize @item @code{__TINYC__} is a predefined macro to @code{'1'} to indicate that you use TCC. @item @code{'#!'} at the start of a line is ignored to allow scripting. @item Binary digits can be entered (@code{'0b101'} instead of @code{'5'}). @item @code{__BOUNDS_CHECKING_ON} is defined if bound checking is activated. @end itemize @node bounds @chapter TinyCC Memory and Bound checks This feature is activated with the @code{'-b'} (@xref{invoke}). Note that pointer size is @emph{unchanged} and that code generated with bound checks is @emph{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. To have more information about the ideas behind this method, check at @url{http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html}. Here are some examples of catched errors: @table @asis @item Invalid range with standard string function: @example { char tab[10]; memset(tab, 0, 11); } @end example @item Bound error in global or local arrays: @example { int tab[10]; for(i=0;i<11;i++) { sum += tab[i]; } } @end example @item Bound error in allocated data: @example { int *tab; tab = malloc(20 * sizeof(int)); for(i=0;i<21;i++) { sum += tab4[i]; } free(tab); } @end example @item Access to a freed region: @example { int *tab; tab = malloc(20 * sizeof(int)); free(tab); for(i=0;i<20;i++) { sum += tab4[i]; } } @end example @item Freeing an already freed region: @example { int *tab; tab = malloc(20 * sizeof(int)); free(tab); free(tab); } @end example @end table @node libtcc @chapter The @code{libtcc} library The @code{libtcc} library enables you to use TCC as a backend for dynamic code generation. Read the @file{libtcc.h} to have an overview of the API. Read @file{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 @code{libtcc}. Then the @code{main()} function of the compiled string can be launched. @chapter Developper'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. @section File reading The @code{BufferedFile} structure contains the context needed to read a file, including the current line number. @code{tcc_open()} opens a new file and @code{tcc_close()} closes it. @code{inp()} returns the next character. @section Lexer @code{next()} reads the next token in the current file. @code{next_nomacro()} reads the next token without macro expansion. @code{tok} contains the current token (see @code{TOK_xxx}) constants. Identifiers and keywords are also keywords. @code{tokc} contains additionnal infos about the token (for example a constant value if number or string token). @section Parser The parser is hardcoded (yacc is not necessary). It does only one pass, except: @itemize @item For initialized arrays with unknown size, a first pass is done to count the number of elements. @item For architectures where arguments are evaluated in reverse order, a first pass is done to reverse the argument order. @end itemize @section 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. @example #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) */ @end example When a reference to another type is needed (for pointers, functions and structures), the @code{32 - VT_STRUCT_SHIFT} high order bits are used to store an identifier reference. The @code{VT_UNSIGNED} flag can be set for chars, shorts, ints and long longs. Arrays are considered as pointers @code{VT_PTR} with the flag @code{VT_ARRAY} set. The @code{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. @code{VT_LONG} is never used except during parsing. During parsing, the storage of an object is also stored in the type integer: @example #define VT_EXTERN 0x00000080 /* extern definition */ #define VT_STATIC 0x00000100 /* static variable */ #define VT_TYPEDEF 0x00000200 /* typedef definition */ @end example @section Symbols All symbols are stored in hashed symbol stacks. Each symbol stack contains @code{Sym} structures. @code{Sym.v} contains the symbol name (remember an idenfier is also a token, so a string is never necessary to store it). @code{Sym.t} gives the type of the symbol. @code{Sym.r} is usually the register in which the corresponding variable is stored. @code{Sym.c} is usually a constant associated to the symbol. Four main symbol stacks are defined: @table @code @item define_stack for the macros (@code{#define}s). @item global_stack for the global variables, functions and types. @item extern_stack for the external symbols shared between files. @item local_stack for the local variables, functions and types. @item label_stack for the local labels (for @code{goto}). @end table @code{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. @code{sym_pop(st,b)} pops symbols from the symbol stack @var{st} until the symbol @var{b} is on the top of stack. If @var{b} is NULL, the stack is emptied. @code{sym_find(v)} return the symbol associated to the identifier @var{v}. The local stack is searched first from top to bottom, then the global stack. @section Sections The generated code and datas are written in sections. The structure @code{Section} contains all the necessary information for a given section. @code{new_section()} creates a new section. ELF file semantics is assumed for each section. The following sections are predefined: @table @code @item text_section is the section containing the generated code. @var{ind} contains the current position in the code section. @item data_section contains initialized data @item bss_section contains uninitialized data @item bounds_section @itemx lbounds_section are used when bound checking is activated @item stab_section @itemx stabstr_section are used when debugging is actived to store debug information @item symtab_section @itemx strtab_section contain the exported symbols (currently only used for debugging). @end table @section Code generation @subsection 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 allows to be very fast and surprisingly not so 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 @emph{value stack}. On x86, three temporary registers are used. When more registers are needed, one register is flushed in a new local variable. @subsection The value stack When an expression is parsed, its value is pushed on the value stack (@var{vstack}). The top of the value stack is @var{vtop}. Each value stack entry is the structure @code{SValue}. @code{SValue.t} is the type. @code{SValue.r} indicates how the value is currently stored in the generated code. It is usually a CPU register index (@code{REG_xxx} constants), but additionnal values and flags are defined: @example #define VT_CONST 0x00f0 /* constant in vc (must be first non register value) */ #define VT_LLOCAL 0x00f1 /* lvalue, offset on stack */ #define VT_LOCAL 0x00f2 /* offset on stack */ #define VT_CMP 0x00f3 /* the value is stored in processor flags (in vc) */ #define VT_JMP 0x00f4 /* value is the consequence of jmp true (even) */ #define VT_JMPI 0x00f5 /* value is the consequence of jmp false (odd) */ #define VT_LVAL 0x0100 /* var is an lvalue */ #define VT_FORWARD 0x0200 /* value is forward reference */ #define VT_MUSTCAST 0x0400 /* value must be casted to be correct (used for char/short stored in integer registers) */ #define VT_MUSTBOUND 0x0800 /* bound checking must be done before dereferencing value */ #define VT_BOUNDED 0x8000 /* value is bounded. The address of the bounding function call point is in vc */ #define VT_LVAL_BYTE 0x1000 /* lvalue is a byte */ #define VT_LVAL_SHORT 0x2000 /* lvalue is a short */ #define VT_LVAL_UNSIGNED 0x4000 /* lvalue is unsigned */ #define VT_LVAL_TYPE (VT_LVAL_BYTE | VT_LVAL_SHORT | VT_LVAL_UNSIGNED) @end example @table @code @item VT_CONST indicates that the value is a constant. It is stored in the union @code{SValue.c}, depending on its type. @item VT_LOCAL indicates a local variable pointer at offset @code{SValue.c.i} in the stack. @item VT_CMP 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}. @item VT_JMP @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. These values are used to compile the @code{||} and @code{&&} logical operators. @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. 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. @item VT_LLOCAL is a saved lvalue on the stack. @code{VT_LLOCAL} should be suppressed ASAP because its semantics are rather complicated. @item VT_MUSTCAST indicates that a cast to the value type must be performed if the value is used (lazy casting). @item VT_FORWARD indicates that the value is a forward reference to a variable or a function. @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). 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. @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.