\input texinfo @c -*- texinfo -*- @c %**start of header @setfilename tcc-doc.info @settitle Tiny C Compiler Reference Documentation @dircategory Software development @direntry * TCC: (tcc-doc). The Tiny C Compiler. @end direntry @c %**end of header @include config.texi @iftex @titlepage @afourpaper @sp 7 @center @titlefont{Tiny C Compiler Reference Documentation} @sp 3 @end titlepage @headings double @end iftex @contents @node Top, Introduction, (dir), (dir) @top Tiny C Compiler Reference Documentation This manual documents version @value{VERSION} of the Tiny C Compiler. @menu * Introduction:: Introduction to tcc. * Invoke:: Invocation of tcc (command line, options). * Clang:: ANSI C and extensions. * asm:: Assembler syntax. * linker:: Output file generation and supported targets. * Bounds:: Automatic bounds-checking of C code. * Libtcc:: The libtcc library. * devel:: Guide for Developers. @end menu @node Introduction @chapter 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 @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 including inline assembly. 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 (@pxref{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 (@pxref{Libtcc}). TCC mainly supports the i386 target on Linux and Windows. There are alpha ports for the ARM (@code{arm-tcc}) and the TMS320C67xx targets (@code{c67-tcc}). More information about the ARM port is available at @url{http://lists.gnu.org/archive/html/tinycc-devel/2003-10/msg00044.html}. For usage on Windows, see also @url{tcc-win32.txt}. @node Invoke @chapter Command line invocation @section Quick start @example @c man begin SYNOPSIS usage: tcc [options] [@var{infile1} @var{infile2}@dots{}] [@option{-run} @var{infile} @var{args}@dots{}] @c man end @end example @noindent @c man begin DESCRIPTION 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: @table @code @item @samp{tcc -run a.c} Compile @file{a.c} and execute it directly @item @samp{tcc -run a.c arg1} Compile a.c and execute it directly. arg1 is given as first argument to the @code{main()} of a.c. @item @samp{tcc a.c -run b.c arg1} Compile @file{a.c} and @file{b.c}, link them together and execute them. arg1 is given as first argument to the @code{main()} of the resulting program. @ignore Because multiple C files are specified, @option{--} are necessary to clearly separate the program arguments from the TCC options. @end ignore @item @samp{tcc -o myprog a.c b.c} Compile @file{a.c} and @file{b.c}, link them and generate the executable @file{myprog}. @item @samp{tcc -o myprog a.o b.o} link @file{a.o} and @file{b.o} together and generate the executable @file{myprog}. @item @samp{tcc -c a.c} Compile @file{a.c} and generate object file @file{a.o}. @item @samp{tcc -c asmfile.S} Preprocess with C preprocess and assemble @file{asmfile.S} and generate object file @file{asmfile.o}. @item @samp{tcc -c asmfile.s} Assemble (but not preprocess) @file{asmfile.s} and generate object file @file{asmfile.o}. @item @samp{tcc -r -o ab.o a.c b.c} Compile @file{a.c} and @file{b.c}, link them together and generate the object file @file{ab.o}. @end table Scripting: TCC can be invoked from @emph{scripts}, just as shell scripts. You just need to add @code{#!/usr/local/bin/tcc -run} at the start of your C source: @example #!/usr/local/bin/tcc -run #include <stdio.h> int main() @{ printf("Hello World\n"); return 0; @} @end example TCC can read C source code from @emph{standard input} when @option{-} is used in place of @option{infile}. Example: @example echo 'main()@{puts("hello");@}' | tcc -run - @end example @c man end @section Option summary General Options: @c man begin OPTIONS @table @option @item -c Generate an object file. @item -o outfile Put object file, executable, or dll into output file @file{outfile}. @item -run source [args...] Compile file @var{source} and run it with the command line arguments @var{args}. In order to be able to give more than one argument to a script, several TCC options can be given @emph{after} the @option{-run} option, separated by spaces: @example tcc "-run -L/usr/X11R6/lib -lX11" ex4.c @end example In a script, it gives the following header: @example #!/usr/local/bin/tcc -run -L/usr/X11R6/lib -lX11 @end example @item -mfloat-abi (ARM only) Select the float ABI. Possible values: @code{softfp} and @code{hard} @item -dumpversion Print only the compiler version and nothing else. @item -v Display TCC version. @item -vv Show included files. As sole argument, print search dirs (as below). @item -bench Display compilation statistics. @item -print-search-dirs Print the configured installation directory and a list of library and include directories tcc will search. @end table Preprocessor options: @table @option @item -Idir 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: @file{/usr/local/include}, @file{/usr/include} and @file{PREFIX/lib/tcc/include}. (@file{PREFIX} is usually @file{/usr} or @file{/usr/local}). @item -Dsym[=val] Define preprocessor symbol @samp{sym} to val. If val is not present, its value is @samp{1}. Function-like macros can also be defined: @option{-DF(a)=a+1} @item -Usym Undefine preprocessor symbol @samp{sym}. @end table Compilation flags: Note: each of the following options has a negative form beginning with @option{-fno-}. @table @option @item -funsigned-char Let the @code{char} type be unsigned. @item -fsigned-char Let the @code{char} type be signed. @item -fno-common Do not generate common symbols for uninitialized data. @item -fleading-underscore Add a leading underscore at the beginning of each C symbol. @item -fms-extensions Allow a MS C compiler extensions to the language. Curretly this assume a nested named structure declaration without identifier behave like an unnamed one. @item -fdollars-in-identifiers Allow a dollars in identifiers. @item -fnormalize-inc-dirs Be more gcc compatible and remove non-existent or duplicate directories from include paths. This helps to compile such packages as coreutils. @end table Warning options: @table @option @item -w Disable all warnings. @end table Note: each of the following warning options has a negative form beginning with @option{-Wno-}. @table @option @item -Wimplicit-function-declaration Warn about implicit function declaration. @item -Wunsupported Warn about unsupported GCC features that are ignored by TCC. @item -Wwrite-strings Make string constants be of type @code{const char *} instead of @code{char *}. @item -Werror Abort compilation if warnings are issued. @item -Wall Activate all warnings, except @option{-Werror}, @option{-Wunusupported} and @option{-Wwrite-strings}. @end table Linker options: @table @option @item -Ldir Specify an additional static library path for the @option{-l} option. The default library paths are @file{/usr/local/lib}, @file{/usr/lib} and @file{/lib}. @item -lxxx Link your program with dynamic library libxxx.so or static library libxxx.a. The library is searched in the paths specified by the @option{-L} option and @env{LIBRARY_PATH} variable. @item -Bdir Set the path where the tcc internal libraries (and include files) can be found (default is @file{PREFIX/lib/tcc}). @item -shared Generate a shared library instead of an executable. @item -soname name set name for shared library to be used at runtime @item -static Generate a statically linked executable (default is a shared linked executable). @item -rdynamic Export global symbols to the dynamic linker. It is useful when a library opened with @code{dlopen()} needs to access executable symbols. @item -r Generate an object file combining all input files. @item -Wl,-rpath=path Put custom search path for dynamic libraries into executable. @item -Wl,--whole-archive Add a whole archive, not just the symbols of the archive that would satisfy undefined symbols in the program. @item -Wl,--no-whole-archive Turn off the effect of the --whole-archive option for subsequent archive files. @item -Wl,--oformat=fmt Use @var{fmt} as output format. The supported output formats are: @table @code @item elf32-i386 ELF output format (default) @item binary Binary image (only for executable output) @item coff COFF output format (only for executable output for TMS320C67xx target) @end table @item -Wl,-subsystem=console/gui/wince/... Set type for PE (Windows) executables. @item -Wl,-[Ttext=# | section-alignment=# | file-alignment=# | image-base=# | stack=#] Modify executable layout. @item -Wl,-Bsymbolic Set DT_SYMBOLIC tag. @end table Debugger options: @table @option @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 additional support code to check memory allocations and array/pointer bounds. @option{-g} is implied. Note that the generated code is slower and bigger in this case. Note: @option{-b} is only available on i386 when using libtcc for the moment. @item -bt N Display N callers in stack traces. This is useful with @option{-g} or @option{-b}. @end table Misc options: @table @option @item -MD Generate makefile fragment with dependencies. @item -MF depfile Use @file{depfile} as output for -MD. @end table Note: GCC options @option{-Ox}, @option{-fx} and @option{-mx} are ignored. @c man end @c man begin ENVIRONMENT Environment variables that affect how tcc operates. @table @option @item CPATH @item C_INCLUDE_PATH A colon-separated list of directories searched for include files, directories given with @option{-I} are searched first. @item LIBRARY_PATH A colon-separated list of directories searched for libraries for the @option{-l} option, directories given with @option{-L} are searched first. @end table @c man end @ignore @setfilename tcc @settitle Tiny C Compiler @c man begin SEEALSO cpp(1), gcc(1) @c man end @c man begin AUTHOR Fabrice Bellard @c man end @end ignore @node Clang @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). @section 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: @itemize @item variable length arrays. @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 @noindent @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 @noindent 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 @dots{} 9: printf("range 1 to 9\n"); break; default: printf("unexpected\n"); break; @} @end example @cindex aligned attribute @cindex packed attribute @cindex section attribute @cindex unused attribute @cindex cdecl attribute @cindex stdcall attribute @cindex regparm attribute @cindex dllexport attribute @item The keyword @code{__attribute__} is handled to specify variable or function attributes. The following attributes are supported: @itemize @item @code{aligned(n)}: align a variable or a structure field to n bytes (must be a power of two). @item @code{packed}: force alignment of a variable or a structure field to 1. @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 (default). @item @code{stdcall}: use Pascal-like calling convention. @item @code{regparm(n)}: use fast i386 calling convention. @var{n} must be between 1 and 3. The first @var{n} function parameters are respectively put in registers @code{%eax}, @code{%edx} and @code{%ecx}. @item @code{dllexport}: export function from dll/executable (win32 only) @end itemize Here are some examples: @example int a __attribute__ ((aligned(8), section(".mysection"))); @end example @noindent 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 @noindent generate function @code{my_add} in section @code{.mycodesection}. @item GNU style variadic macros: @example #define dprintf(fmt, args@dots{}) printf(fmt, ## args) dprintf("no arg\n"); dprintf("one arg %d\n", 1); @end example @item @code{__FUNCTION__} is interpreted as C99 @code{__func__} (so it has not exactly the same semantics as string literal GNUC where it is a string literal). @item The @code{__alignof__} keyword can be used as @code{sizeof} to get the alignment of a type or an expression. @item The @code{typeof(x)} returns the type of @code{x}. @code{x} is an expression or a type. @item Computed gotos: @code{&&label} returns a pointer of type @code{void *} on the goto label @code{label}. @code{goto *expr} can be used to jump on the pointer resulting from @code{expr}. @item Inline assembly with asm instruction: @cindex inline assembly @cindex assembly, inline @cindex __asm__ @example static inline void * my_memcpy(void * to, const void * from, size_t n) @{ int d0, d1, d2; __asm__ __volatile__( "rep ; movsl\n\t" "testb $2,%b4\n\t" "je 1f\n\t" "movsw\n" "1:\ttestb $1,%b4\n\t" "je 2f\n\t" "movsb\n" "2:" : "=&c" (d0), "=&D" (d1), "=&S" (d2) :"0" (n/4), "q" (n),"1" ((long) to),"2" ((long) from) : "memory"); return (to); @} @end example @noindent @cindex gas TCC includes its own x86 inline assembler with a @code{gas}-like (GNU assembler) syntax. No intermediate files are generated. GCC 3.x named operands are supported. @item @code{__builtin_types_compatible_p()} and @code{__builtin_constant_p()} are supported. @item @code{#pragma pack} is supported for win32 compatibility. @end itemize @section TinyCC extensions @itemize @item @code{__TINYC__} is a predefined macro to indicate that you use TCC. @item @code{#!} at the start of a line is ignored to allow scripting. @item Binary digits can be entered (@code{0b101} instead of @code{5}). @item @code{__BOUNDS_CHECKING_ON} is defined if bound checking is activated. @end itemize @node asm @chapter TinyCC Assembler Since version 0.9.16, TinyCC integrates its own assembler. TinyCC assembler supports a gas-like syntax (GNU assembler). You can desactivate assembler support if you want a smaller TinyCC executable (the C compiler does not rely on the assembler). TinyCC Assembler is used to handle files with @file{.S} (C preprocessed assembler) and @file{.s} extensions. It is also used to handle the GNU inline assembler with the @code{asm} keyword. @section Syntax TinyCC Assembler supports most of the gas syntax. The tokens are the same as C. @itemize @item C and C++ comments are supported. @item Identifiers are the same as C, so you cannot use '.' or '$'. @item Only 32 bit integer numbers are supported. @end itemize @section Expressions @itemize @item Integers in decimal, octal and hexa are supported. @item Unary operators: +, -, ~. @item Binary operators in decreasing priority order: @enumerate @item *, /, % @item &, |, ^ @item +, - @end enumerate @item A value is either an absolute number or a label plus an offset. All operators accept absolute values except '+' and '-'. '+' or '-' can be used to add an offset to a label. '-' supports two labels only if they are the same or if they are both defined and in the same section. @end itemize @section Labels @itemize @item All labels are considered as local, except undefined ones. @item Numeric labels can be used as local @code{gas}-like labels. They can be defined several times in the same source. Use 'b' (backward) or 'f' (forward) as suffix to reference them: @example 1: jmp 1b /* jump to '1' label before */ jmp 1f /* jump to '1' label after */ 1: @end example @end itemize @section Directives @cindex assembler directives @cindex directives, assembler @cindex align directive @cindex skip directive @cindex space directive @cindex byte directive @cindex word directive @cindex short directive @cindex int directive @cindex long directive @cindex quad directive @cindex globl directive @cindex global directive @cindex section directive @cindex text directive @cindex data directive @cindex bss directive @cindex fill directive @cindex org directive @cindex previous directive @cindex string directive @cindex asciz directive @cindex ascii directive All directives are preceded by a '.'. The following directives are supported: @itemize @item .align n[,value] @item .skip n[,value] @item .space n[,value] @item .byte value1[,...] @item .word value1[,...] @item .short value1[,...] @item .int value1[,...] @item .long value1[,...] @item .quad immediate_value1[,...] @item .globl symbol @item .global symbol @item .section section @item .text @item .data @item .bss @item .fill repeat[,size[,value]] @item .org n @item .previous @item .string string[,...] @item .asciz string[,...] @item .ascii string[,...] @end itemize @section X86 Assembler @cindex 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. @node linker @chapter TinyCC Linker @cindex linker @section ELF file generation @cindex ELF 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 (@option{--start-group} and @option{--end-group}) are supported. @section ELF file loader TCC can load ELF object files, archives (.a files) and dynamic libraries (.so). @section PE-i386 file generation @cindex PE-i386 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. @section GNU Linker Scripts @cindex scripts, linker @cindex linker scripts @cindex GROUP, linker command @cindex FILE, linker command @cindex OUTPUT_FORMAT, linker command @cindex TARGET, linker command Because on many Linux systems some dynamic libraries (such as @file{/usr/lib/libc.so}) are in fact GNU ld link scripts (horrible!), the TCC linker also supports a subset of GNU ld scripts. The @code{GROUP} and @code{FILE} commands are supported. @code{OUTPUT_FORMAT} and @code{TARGET} are ignored. Example from @file{/usr/lib/libc.so}: @example /* 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 ) @end example @node Bounds @chapter TinyCC Memory and Bound checks @cindex bound checks @cindex memory checks This feature is activated with the @option{-b} (@pxref{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. For more information about the ideas behind this method, see @url{http://www.doc.ic.ac.uk/~phjk/BoundsChecking.html}. Here are some examples of caught errors: @table @asis @item Invalid range with standard string function: @example @{ char tab[10]; memset(tab, 0, 11); @} @end example @item Out of bounds-error in global or local arrays: @example @{ int tab[10]; for(i=0;i<11;i++) @{ sum += tab[i]; @} @} @end example @item Out of bounds-error in malloc'ed data: @example @{ int *tab; tab = malloc(20 * sizeof(int)); for(i=0;i<21;i++) @{ sum += tab4[i]; @} free(tab); @} @end example @item Access of freed memory: @example @{ int *tab; tab = malloc(20 * sizeof(int)); free(tab); for(i=0;i<20;i++) @{ sum += tab4[i]; @} @} @end example @item Double free: @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 you can access to any global symbol (function or variable) defined. @node devel @chapter 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. @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 additional 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 chosen 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_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) */ @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. Variable length arrays are considered as special arrays and have flag @code{VT_VLA} set instead of @code{VT_ARRAY}. 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 */ #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 */ @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 like its address for normal symbols, and the number of entries for symbols representing arrays. Variable length array types use @code{Sym.c} as a location on the stack which holds the runtime sizeof for the type. 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 local_stack for the local variables, functions and types. @item global_label_stack for the local labels (for @code{goto}). @item label_stack for GCC block local labels (see the @code{__label__} keyword). @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 active to store debug information @item symtab_section @itemx strtab_section contain the exported symbols (currently only used for debugging). @end table @section Code generation @cindex 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 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 @emph{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. @subsection The value stack @cindex value stack, introduction 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 additional values and flags are defined: @example #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 #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}. If any code is generated which destroys the CPU flags, this value MUST be put in a normal register. @item VT_JMP @itemx VT_JMPI 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 @code{||} and @code{&&} 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. @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 enough in case of cast optimisations. @item VT_LLOCAL is a saved lvalue on the stack. @code{VT_LVAL} must also be set with @code{VT_LLOCAL}. @code{VT_LLOCAL} can arise when a @code{VT_LVAL} in a register has to be saved to the stack, or it can come from an architecture-specific calling convention. @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 @cindex value stack @code{vsetc()} and @code{vset()} pushes a new value on the value stack. If the previous @var{vtop} was stored in a very unsafe place(for example in the CPU flags), then some code is generated to put the previous @var{vtop} in a safe storage. @code{vpop()} pops @var{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 @var{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 @cindex CPU dependent 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 bounds checking. @end table @section Optimizations done @cindex optimizations @cindex constant propagation @cindex strength reduction @cindex comparison operators @cindex caching processor flags @cindex flags, caching @cindex jump optimization 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. @unnumbered Concept Index @printindex cp @bye @c Local variables: @c fill-column: 78 @c texinfo-column-for-description: 32 @c End: