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GNU Info File | 1993-06-20 | 21.7 KB | 515 lines

This is Info file gcc.info, produced by Makeinfo-1.54 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "GNU General Public License" and "Protect Your Freedom--Fight `Look And Feel'" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public License" and "Protect Your Freedom--Fight `Look And Feel'", and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English. File: gcc.info, Node: DEC Alpha Options, Next: System V Options, Prev: Intel 960 Options, Up: Submodel Options DEC Alpha Options ----------------- These `-m' options are defined for the DEC Alpha implementations: `-mno-soft-float' `-msoft-float' Use (do not use) the hardware floating-point instructions for floating-point operations. When `-msoft-float' is specified, functions in `libgcc1.c' will be used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines will issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating-point operations are required to have floating-point registers. `-mfp-reg' `-mno-fp-regs' Generate code that uses (does not use) the floating-point register set. `-mno-fp-regs' implies `-msoft-float'. If the floating-point register set is not used, floating point operands are passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with `-mno-fp-regs' must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers. File: gcc.info, Node: System V Options, Prev: DEC Alpha Options, Up: Submodel Options Options for System V -------------------- These additional options are available on System V Release 4 for compatibility with other compilers on those systems: `-Qy' Identify the versions of each tool used by the compiler, in a `.ident' assembler directive in the output. `-Qn' Refrain from adding `.ident' directives to the output file (this is the default). `-YP,DIRS' Search the directories DIRS, and no others, for libraries specified with `-l'. `-Ym,DIR' Look in the directory DIR to find the M4 preprocessor. The assembler uses this option. File: gcc.info, Node: Code Gen Options, Next: Environment Variables, Prev: Submodel Options, Up: Invoking GCC Options for Code Generation Conventions ======================================= These machine-independent options control the interface conventions used in code generation. Most of them have both positive and negative forms; the negative form of `-ffoo' would be `-fno-foo'. In the table below, only one of the forms is listed--the one which is not the default. You can figure out the other form by either removing `no-' or adding it. `-fpcc-struct-return' Return "short" `struct' and `union' values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GNU CC-compiled files and files compiled with other compilers. The precise convention for returning structures in memory depends on the target configuration macros. Short structures and unions are those whose size and alignment match that of some integer type. `-freg-struct-return' Use the convention that `struct' and `union' values are returned in registers when possible. This is more efficient for small structures than `-fpcc-struct-return'. If you specify neither `-fpcc-struct-return' nor its contrary `-freg-struct-return', GNU CC defaults to whichever convention is standard for the target. If there is no standard convention, GNU CC defaults to `-fpcc-struct-return', except on targets where GNU CC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. `-fshort-enums' Allocate to an `enum' type only as many bytes as it needs for the declared range of possible values. Specifically, the `enum' type will be equivalent to the smallest integer type which has enough room. `-fshort-double' Use the same size for `double' as for `float'. `-fshared-data' Requests that the data and non-`const' variables of this compilation be shared data rather than private data. The distinction makes sense only on certain operating systems, where shared data is shared between processes running the same program, while private data exists in one copy per process. `-fno-common' Allocate even uninitialized global variables in the bss section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without `extern') in two different compilations, you will get an error when you link them. The only reason this might be useful is if you wish to verify that the program will work on other systems which always work this way. `-fno-ident' Ignore the `#ident' directive. `-fno-gnu-linker' Do not output global initializations (such as C++ constructors and destructors) in the form used by the GNU linker (on systems where the GNU linker is the standard method of handling them). Use this option when you want to use a non-GNU linker, which also requires using the `collect2' program to make sure the system linker includes constructors and destructors. (`collect2' is included in the GNU CC distribution.) For systems which *must* use `collect2', the compiler driver `gcc' is configured to do this automatically. `-finhibit-size-directive' Don't output a `.size' assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling `crtstuff.c'; you should not need to use it for anything else. `-fverbose-asm' Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). `-fvolatile' Consider all memory references through pointers to be volatile. `-fvolatile-global' Consider all memory references to extern and global data items to be volatile. `-fpic' Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (GOT). If the GOT size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that `-fpic' does not work; in that case, recompile with `-fPIC' instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k on the m68k and RS/6000. The 386 has no such limit.) Position-independent code requires special support, and therefore works only on certain machines. For the 386, GNU CC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent. The GNU assembler does not fully support PIC. Currently, you must use some other assembler in order for PIC to work. We would welcome volunteers to upgrade GAS to handle this; the first part of the job is to figure out what the assembler must do differently. `-fPIC' If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, m88k and the Sparc. Position-independent code requires special support, and therefore works only on certain machines. `-ffixed-REG' Treat the register named REG as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). REG must be the name of a register. The register names accepted are machine-specific and are defined in the `REGISTER_NAMES' macro in the machine description macro file. This flag does not have a negative form, because it specifies a three-way choice. `-fcall-used-REG' Treat the register named REG as an allocatable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way will not save and restore the register REG. Use of this flag for a register that has a fixed pervasive role in the machine's execution model, such as the stack pointer or frame pointer, will produce disastrous results. This flag does not have a negative form, because it specifies a three-way choice. `-fcall-saved-REG' Treat the register named REG as an allocatable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way will save and restore the register REG if they use it. Use of this flag for a register that has a fixed pervasive role in the machine's execution model, such as the stack pointer or frame pointer, will produce disastrous results. A different sort of disaster will result from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it specifies a three-way choice. `+e0' `+e1' Control whether virtual function definitions in classes are used to generate code, or only to define interfaces for their callers. (C++ only). These options are provided for compatibility with `cfront' 1.x usage; the recommended alternative GNU C++ usage is in flux. *Note Declarations and Definitions in One Header: C++ Interface. With `+e0', virtual function definitions in classes are declared `extern'; the declaration is used only as an interface specification, not to generate code for the virtual functions (in this compilation). With `+e1', G++ actually generates the code implementing virtual functions defined in the code, and makes them publicly visible. File: gcc.info, Node: Environment Variables, Next: Running Protoize, Prev: Code Gen Options, Up: Invoking GCC Environment Variables Affecting GNU CC ====================================== This section describes several environment variables that affect how GNU CC operates. They work by specifying directories or prefixes to use when searching for various kinds of files. Note that you can also specify places to search using options such as `-B', `-I' and `-L' (*note Directory Options::.). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GNU CC. *Note Driver::. `TMPDIR' If `TMPDIR' is set, it specifies the directory to use for temporary files. GNU CC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. `GCC_EXEC_PREFIX' If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. If GNU CC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. Other prefixes specified with `-B' take precedence over this prefix. This prefix is also used for finding files such as `crt0.o' that are used for linking. In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with `/usr/local/lib/gcc-lib' (more precisely, with the value of `GCC_INCLUDE_DIR'), GNU CC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with `-Bfoo/', GNU CC will search `foo/bar' where it would normally search `/usr/local/lib/bar'. These alternate directories are searched first; the standard directories come next. `COMPILER_PATH' The value of `COMPILER_PATH' is a colon-separated list of directories, much like `PATH'. GNU CC tries the directories thus specified when searching for subprograms, if it can't find the subprograms using `GCC_EXEC_PREFIX'. `LIBRARY_PATH' The value of `LIBRARY_PATH' is a colon-separated list of directories, much like `PATH'. GNU CC tries the directories thus specified when searching for special linker files, if it can't find them using `GCC_EXEC_PREFIX'. Linking using GNU CC also uses these directories when searching for ordinary libraries for the `-l' option (but directories specified with `-L' come first). `C_INCLUDE_PATH' `CPLUS_INCLUDE_PATH' `OBJC_INCLUDE_PATH' These environment variables pertain to particular languages. Each variable's value is a colon-separated list of directories, much like `PATH'. When GNU CC searches for header files, it tries the directories listed in the variable for the language you are using, after the directories specified with `-I' but before the standard header file directories. `DEPENDENCIES_OUTPUT' If this variable is set, its value specifies how to output dependencies for Make based on the header files processed by the compiler. This output looks much like the output from the `-M' option (*note Preprocessor Options::.), but it goes to a separate file, and is in addition to the usual results of compilation. The value of `DEPENDENCIES_OUTPUT' can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form `FILE TARGET', in which case the rules are written to file FILE using TARGET as the target name. File: gcc.info, Node: Running Protoize, Prev: Environment Variables, Up: Invoking GCC Running Protoize ================ The program `protoize' is an optional part of GNU C. You can use it to add prototypes to a program, thus converting the program to ANSI C in one respect. The companion program `unprotoize' does the reverse: it removes argument types from any prototypes that are found. When you run these programs, you must specify a set of source files as command line arguments. The conversion programs start out by compiling these files to see what functions they define. The information gathered about a file FOO is saved in a file named `FOO.X'. After scanning comes actual conversion. The specified files are all eligible to be converted; any files they include (whether sources or just headers) are eligible as well. But not all the eligible files are converted. By default, `protoize' and `unprotoize' convert only source and header files in the current directory. You can specify additional directories whose files should be converted with the `-d DIRECTORY' option. You can also specify particular files to exclude with the `-x FILE' option. A file is converted if it is eligible, its directory name matches one of the specified directory names, and its name within the directory has not been excluded. Basic conversion with `protoize' consists of rewriting most function definitions and function declarations to specify the types of the arguments. The only ones not rewritten are those for varargs functions. `protoize' optionally inserts prototype declarations at the beginning of the source file, to make them available for any calls that precede the function's definition. Or it can insert prototype declarations with block scope in the blocks where undeclared functions are called. Basic conversion with `unprotoize' consists of rewriting most function declarations to remove any argument types, and rewriting function definitions to the old-style pre-ANSI form. Both conversion programs print a warning for any function declaration or definition that they can't convert. You can suppress these warnings with `-q'. The output from `protoize' or `unprotoize' replaces the original source file. The original file is renamed to a name ending with `.save'. If the `.save' file already exists, then the source file is simply discarded. `protoize' and `unprotoize' both depend on GNU CC itself to scan the program and collect information about the functions it uses. So neither of these programs will work until GNU CC is installed. Here is a table of the options you can use with `protoize' and `unprotoize'. Each option works with both programs unless otherwise stated. `-B DIRECTORY' Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the usual directory (normally `/usr/local/lib'). This file contains prototype information about standard system functions. This option applies only to `protoize'. `-c COMPILATION-OPTIONS' Use COMPILATION-OPTIONS as the options when running `gcc' to produce the `.X' files. The special option `-aux-info' is always passed in addition, to tell `gcc' to write a `.X' file. Note that the compilation options must be given as a single argument to `protoize' or `unprotoize'. If you want to specify several `gcc' options, you must quote the entire set of compilation options to make them a single word in the shell. There are certain `gcc' arguments that you cannot use, because they would produce the wrong kind of output. These include `-g', `-O', `-c', `-S', and `-o' If you include these in the COMPILATION-OPTIONS, they are ignored. `-C' Rename files to end in `.C' instead of `.c'. This is convenient if you are converting a C program to C++. This option applies only to `protoize'. `-g' Add explicit global declarations. This means inserting explicit declarations at the beginning of each source file for each function that is called in the file and was not declared. These declarations precede the first function definition that contains a call to an undeclared function. This option applies only to `protoize'. `-i STRING' Indent old-style parameter declarations with the string STRING. This option applies only to `protoize'. `unprotoize' converts prototyped function definitions to old-style function definitions, where the arguments are declared between the argument list and the initial `{'. By default, `unprotoize' uses five spaces as the indentation. If you want to indent with just one space instead, use `-i " "'. `-k' Keep the `.X' files. Normally, they are deleted after conversion is finished. `-l' Add explicit local declarations. `protoize' with `-l' inserts a prototype declaration for each function in each block which calls the function without any declaration. This option applies only to `protoize'. `-n' Make no real changes. This mode just prints information about the conversions that would have been done without `-n'. `-N' Make no `.save' files. The original files are simply deleted. Use this option with caution. `-p PROGRAM' Use the program PROGRAM as the compiler. Normally, the name `gcc' is used. `-q' Work quietly. Most warnings are suppressed. `-v' Print the version number, just like `-v' for `gcc'. If you need special compiler options to compile one of your program's source files, then you should generate that file's `.X' file specially, by running `gcc' on that source file with the appropriate options and the option `-aux-info'. Then run `protoize' on the entire set of files. `protoize' will use the existing `.X' file because it is newer than the source file. For example: gcc -Dfoo=bar file1.c -aux-info protoize *.c You need to include the special files along with the rest in the `protoize' command, even though their `.X' files already exist, because otherwise they won't get converted. *Note Protoize Caveats::, for more information on how to use `protoize' successfully.