This is Info file gcc.info, produced by Makeinfo-1.55 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, 1994 Free Software Foundation, 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," "Funding for Free Software," 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," "Funding for Free Software," 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: Debugging Options, Next: Optimize Options, Prev: Warning Options, Up: Invoking GCC Options for Debugging Your Program or GNU CC ============================================ GNU CC has various special options that are used for debugging either your program or GCC: Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging information. On most systems that use stabs format, `-g' enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but will probably make other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', `-gdwarf+', or `-gdwarf' (see below). Unlike most other C compilers, GNU CC allows you to use `-g' with `-O'. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values were already at hand; some statements may execute in different places because they were moved out of loops. Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. The following options are useful when GNU CC is generated with the capability for more than one debugging format. `-ggdb' Produce debugging information in the native format (if that is supported), including GDB extensions if at all possible. `-gstabs' Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. On MIPS, Alpha and System V Release 4 systems this option produces stabs debugging output which is not understood by DBX or SDB. On System V Release 4 systems this option requires the GNU assembler. `-gstabs+' Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash or refuse to read the program. `-gcoff' Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4. `-gxcoff' Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems. `-gxcoff+' Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash or refuse to read the program. `-gdwarf' Produce debugging information in DWARF format (if that is supported). This is the format used by SDB on most System V Release 4 systems. `-gdwarf+' Produce debugging information in DWARF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash or refuse to read the program. `-gLEVEL' `-ggdbLEVEL' `-gstabsLEVEL' `-gcoffLEVEL' `-gxcoffLEVEL' `-gdwarfLEVEL' Request debugging information and also use LEVEL to specify how much information. The default level is 2. Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, but no information about local variables and no line numbers. Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use `-g3'. Generate extra code to write profile information suitable for the analysis program `prof'. You must use this option when compiling the source files you want data about, and you must also use it when linking. `-pg' Generate extra code to write profile information suitable for the analysis program `gprof'. You must use this option when compiling the source files you want data about, and you must also use it when linking. Generate extra code to write profile information for basic blocks, which will record the number of times each basic block is executed, the basic block start address, and the function name containing the basic block. If `-g' is used, the line number and filename of the start of the basic block will also be recorded. If not overridden by the machine description, the default action is to append to the text file `bb.out'. This data could be analyzed by a program like `tcov'. Note, however, that the format of the data is not what `tcov' expects. Eventually GNU `gprof' should be extended to process this data. `-dLETTERS' Says to make debugging dumps during compilation at times specified by LETTERS. This is used for debugging the compiler. The file names for most of the dumps are made by appending a word to the source file name (e.g. `foo.c.rtl' or `foo.c.jump'). Here are the possible letters for use in LETTERS, and their meanings: `M' Dump all macro definitions, at the end of preprocessing, and write no output. `N' Dump all macro names, at the end of preprocessing. `D' Dump all macro definitions, at the end of preprocessing, in addition to normal output. `y' Dump debugging information during parsing, to standard error. `r' Dump after RTL generation, to `FILE.rtl'. `x' Just generate RTL for a function instead of compiling it. Usually used with `r'. `j' Dump after first jump optimization, to `FILE.jump'. `s' Dump after CSE (including the jump optimization that sometimes follows CSE), to `FILE.cse'. `L' Dump after loop optimization, to `FILE.loop'. `t' Dump after the second CSE pass (including the jump optimization that sometimes follows CSE), to `FILE.cse2'. `f' Dump after flow analysis, to `FILE.flow'. `c' Dump after instruction combination, to the file `FILE.combine'. `S' Dump after the first instruction scheduling pass, to `FILE.sched'. `l' Dump after local register allocation, to `FILE.lreg'. `g' Dump after global register allocation, to `FILE.greg'. `R' Dump after the second instruction scheduling pass, to `FILE.sched2'. `J' Dump after last jump optimization, to `FILE.jump2'. `d' Dump after delayed branch scheduling, to `FILE.dbr'. `k' Dump after conversion from registers to stack, to `FILE.stack'. `a' Produce all the dumps listed above. `m' Print statistics on memory usage, at the end of the run, to standard error. `p' Annotate the assembler output with a comment indicating which pattern and alternative was used. `-fpretend-float' When running a cross-compiler, pretend that the target machine uses the same floating point format as the host machine. This causes incorrect output of the actual floating constants, but the actual instruction sequence will probably be the same as GNU CC would make when running on the target machine. `-save-temps' Store the usual "temporary" intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling `foo.c' with `-c -save-temps' would produce files `foo.i' and `foo.s', as well as `foo.o'. `-print-file-name=LIBRARY' Print the full absolute name of the library file LIBRARY that would be used when linking--and don't do anything else. With this option, GNU CC does not compile or link anything; it just prints the file name. `-print-prog-name=PROGRAM' Like `-print-file-name', but searches for a program such as `cpp'. `-print-libgcc-file-name' Same as `-print-file-name=libgcc.a'. This is useful when you use `-nostdlib' but you do want to link with `libgcc.a'. You can do gcc -nostdlib FILES... `gcc -print-libgcc-file-name` File: gcc.info, Node: Optimize Options, Next: Preprocessor Options, Prev: Debugging Options, Up: Invoking GCC Options That Control Optimization ================================= These options control various sorts of optimizations: `-O1' Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. Without `-O', the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code. Without `-O', the compiler only allocates variables declared `register' in registers. The resulting compiled code is a little worse than produced by PCC without `-O'. With `-O', the compiler tries to reduce code size and execution time. When you specify `-O', the compiler turns on `-fthread-jumps' and `-fdefer-pop' on all machines. The compiler turns on `-fdelayed-branch' on machines that have delay slots, and `-fomit-frame-pointer' on machines that can support debugging even without a frame pointer. On some machines the compiler also turns on other flags. `-O2' Optimize even more. GNU CC performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify `-O2'. As compared to `-O', this option increases both compilation time and the performance of the generated code. `-O2' turns on all optional optimizations except for loop unrolling and function inlining. It also turns on frame pointer elimination on machines where doing so does not interfer with debugging. `-O3' Optimize yet more. `-O3' turns on all optimizations specified by `-O2' and also turns on the `inline-functions' option. `-O0' Do not optimize. If you use multiple `-O' options, with or without level numbers, the last such option is the one that is effective. Options of the form `-fFLAG' specify machine-independent flags. Most flags 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. `-ffloat-store' Do not store floating point variables in registers, and inhibit other options that might change whether a floating point value is taken from a register or memory. This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a `double' is supposed to have. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use `-ffloat-store' for such programs. `-fno-default-inline' Do not make member functions inline by default merely because they are defined inside the class scope (C++ only). Otherwise, when you specify `-O', member functions defined inside class scope are compiled inline by default; i.e., you don't need to add `inline' in front of the member function name. `-fno-defer-pop' Always pop the arguments to each function call as soon as that function returns. For machines which must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. `-fforce-mem' Force memory operands to be copied into registers before doing arithmetic on them. This may produce better code by making all memory references potential common subexpressions. When they are not common subexpressions, instruction combination should eliminate the separate register-load. I am interested in hearing about the difference this makes. `-fforce-addr' Force memory address constants to be copied into registers before doing arithmetic on them. This may produce better code just as `-fforce-mem' may. I am interested in hearing about the difference this makes. `-fomit-frame-pointer' Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. *It also makes debugging impossible on some machines.* On some machines, such as the Vax, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro `FRAME_POINTER_REQUIRED' controls whether a target machine supports this flag. *Note Registers::. `-fno-inline' Don't pay attention to the `inline' keyword. Normally this option is used to keep the compiler from expanding any functions inline. Note that if you are not optimizing, no functions can be expanded inline. `-finline-functions' Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be worth integrating in this way. If all calls to a given function are integrated, and the function is declared `static', then the function is normally not output as assembler code in its own right. `-fkeep-inline-functions' Even if all calls to a given function are integrated, and the function is declared `static', nevertheless output a separate run-time callable version of the function. `-fno-function-cse' Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. `-ffast-math' This option allows GCC to violate some ANSI or IEEE rules and/or specifications in the interest of optimizing code for speed. For example, it allows the compiler to assume arguments to the `sqrt' function are non-negative numbers and that no floating-point values are NaNs. This option should never be turned on by any `-O' option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ANSI rules/specifications for math functions. The following options control specific optimizations. The `-O2' option turns on all of these optimizations except `-funroll-loops' and `-funroll-all-loops'. On most machines, the `-O' option turns on the `-fthread-jumps' and `-fdelayed-branch' options, but specific machines may handle it differently. You can use the following flags in the rare cases when "fine-tuning" of optimizations to be performed is desired. `-fstrength-reduce' Perform the optimizations of loop strength reduction and elimination of iteration variables. `-fthread-jumps' Perform optimizations where we check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. `-fcse-follow-jumps' In common subexpression elimination, scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an `if' statement with an `else' clause, CSE will follow the jump when the condition tested is false. `-fcse-skip-blocks' This is similar to `-fcse-follow-jumps', but causes CSE to follow jumps which conditionally skip over blocks. When CSE encounters a simple `if' statement with no else clause, `-fcse-skip-blocks' causes CSE to follow the jump around the body of the `if'. `-frerun-cse-after-loop' Re-run common subexpression elimination after loop optimizations has been performed. `-fexpensive-optimizations' Perform a number of minor optimizations that are relatively expensive. `-fdelayed-branch' If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. `-fschedule-insns' If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating point instruction is required. `-fschedule-insns2' Similar to `-fschedule-insns', but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. `-fcaller-saves' Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced. This option is enabled by default on certain machines, usually those which have no call-preserved registers to use instead. `-funroll-loops' Perform the optimization of loop unrolling. This is only done for loops whose number of iterations can be determined at compile time or run time. `-funroll-loop' implies both `-fstrength-reduce' and `-frerun-cse-after-loop'. `-funroll-all-loops' Perform the optimization of loop unrolling. This is done for all loops and usually makes programs run more slowly. `-funroll-all-loops' implies `-fstrength-reduce' as well as `-frerun-cse-after-loop'. `-fno-peephole' Disable any machine-specific peephole optimizations. File: gcc.info, Node: Preprocessor Options, Next: Assembler Options, Prev: Optimize Options, Up: Invoking GCC Options Controlling the Preprocessor ==================================== These options control the C preprocessor, which is run on each C source file before actual compilation. If you use the `-E' option, nothing is done except preprocessing. Some of these options make sense only together with `-E' because they cause the preprocessor output to be unsuitable for actual compilation. `-include FILE' Process FILE as input before processing the regular input file. In effect, the contents of FILE are compiled first. Any `-D' and `-U' options on the command line are always processed before `-include FILE', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written. `-imacros FILE' Process FILE as input, discarding the resulting output, before processing the regular input file. Because the output generated from FILE is discarded, the only effect of `-imacros FILE' is to make the macros defined in FILE available for use in the main input. Any `-D' and `-U' options on the command line are always processed before `-imacros FILE', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written. `-idirafter DIR' Add the directory DIR to the second include path. The directories on the second include path are searched when a header file is not found in any of the directories in the main include path (the one that `-I' adds to). `-iprefix PREFIX' Specify PREFIX as the prefix for subsequent `-iwithprefix' options. `-iwithprefix DIR' Add a directory to the second include path. The directory's name is made by concatenating PREFIX and DIR, where PREFIX was specified previously with `-iprefix'. If you have not specified a prefix yet, the directory containing the installed passes of the compiler is used as the default. `-iwithprefixbefore DIR' Add a directory to the main include path. The directory's name is made by concatenating PREFIX and DIR, as in the case of `-iwithprefix'. `-isystem DIR' Add a directory to the beginning of the second include path, marking it as a system directory, so that it gets the same special treatment as is applied to the standard system directories. `-nostdinc' Do not search the standard system directories for header files. Only the directories you have specified with `-I' options (and the current directory, if appropriate) are searched. *Note Directory Options::, for information on `-I'. By using both `-nostdinc' and `-I-', you can limit the include-file search path to only those directories you specify explicitly. `-undef' Do not predefine any nonstandard macros. (Including architecture flags). Run only the C preprocessor. Preprocess all the C source files specified and output the results to standard output or to the specified output file. Tell the preprocessor not to discard comments. Used with the `-E' option. Tell the preprocessor not to generate `#line' commands. Used with the `-E' option. Tell the preprocessor to output a rule suitable for `make' describing the dependencies of each object file. For each source file, the preprocessor outputs one `make'-rule whose target is the object file name for that source file and whose dependencies are all the `#include' header files it uses. This rule may be a single line or may be continued with `\'-newline if it is long. The list of rules is printed on standard output instead of the preprocessed C program. `-M' implies `-E'. Another way to specify output of a `make' rule is by setting the environment variable `DEPENDENCIES_OUTPUT' (*note Environment Variables::.). `-MM' Like `-M' but the output mentions only the user header files included with `#include "FILE"'. System header files included with `#include ' are omitted. `-MD' Like `-M' but the dependency information is written to a file made by replacing ".c" with ".d" at the end of the input file names. This is in addition to compiling the file as specified--`-MD' does not inhibit ordinary compilation the way `-M' does. In Mach, you can use the utility `md' to merge multiple dependency files into a single dependency file suitable for using with the `make' command. `-MMD' Like `-MD' except mention only user header files, not system header files. `-MG' Treat missing header files as generated files and assume they live in the same directory as the source file. If you specify `-MG', you must also specify either `-M' or `-MM'. `-MG' is not supported with `-MD' or `-MMD'. Print the name of each header file used, in addition to other normal activities. `-AQUESTION(ANSWER)' Assert the answer ANSWER for QUESTION, in case it is tested with a preprocessor conditional such as `#if #QUESTION(ANSWER)'. `-A-' disables the standard assertions that normally describe the target machine. `-DMACRO' Define macro MACRO with the string `1' as its definition. `-DMACRO=DEFN' Define macro MACRO as DEFN. All instances of `-D' on the command line are processed before any `-U' options. `-UMACRO' Undefine macro MACRO. `-U' options are evaluated after all `-D' options, but before any `-include' and `-imacros' options. `-dM' Tell the preprocessor to output only a list of the macro definitions that are in effect at the end of preprocessing. Used with the `-E' option. `-dD' Tell the preprocessing to pass all macro definitions into the output, in their proper sequence in the rest of the output. `-dN' Like `-dD' except that the macro arguments and contents are omitted. Only `#define NAME' is included in the output. `-trigraphs' Support ANSI C trigraphs. The `-ansi' option also has this effect. `-Wp,OPTION' Pass OPTION as an option to the preprocessor. If OPTION contains commas, it is split into multiple options at the commas. File: gcc.info, Node: Assembler Options, Next: Link Options, Prev: Preprocessor Options, Up: Invoking GCC Passing Options to the Assembler ================================ You can pass options to the assembler. `-Wa,OPTION' Pass OPTION as an option to the assembler. If OPTION contains commas, it is split into multiple options at the commas. File: gcc.info, Node: Link Options, Next: Directory Options, Prev: Assembler Options, Up: Invoking GCC Options for Linking =================== These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. `OBJECT-FILE-NAME' A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. If any of these options is used, then the linker is not run, and object file names should not be used as arguments. *Note Overall Options::. `-lLIBRARY' Search the library named LIBRARY when linking. It makes a difference where in the command you write this option; the linker searches processes libraries and object files in the order they are specified. Thus, `foo.o -lz bar.o' searches library `z' after file `foo.o' but before `bar.o'. If `bar.o' refers to functions in `z', those functions may not be loaded. The linker searches a standard list of directories for the library, which is actually a file named `libLIBRARY.a'. The linker then uses this file as if it had been specified precisely by name. The directories searched include several standard system directories plus any that you specify with `-L'. Normally the files found this way are library files--archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an `-l' option and specifying a file name is that `-l' surrounds LIBRARY with `lib' and `.a' and searches several directories. `-lobjc' You need this special case of the `-l' option in order to link an Objective C program. `-nostartfiles' Do not use the standard system startup files when linking. The standard libraries are used normally. `-nostdlib' Do not use the standard system libraries and startup files when linking. Only the files you specify will be passed to the linker. One of the standard libraries bypassed by `-nostdlib' is `libgcc.a', a library of internal subroutines that GNU CC uses to overcome shortcomings of particular machines, or special needs for some languages. (*Note Interfacing to GNU CC Output: Interface, for more discussion of `libgcc.a'.) In most cases, you need `libgcc.a' even when you want to avoid other standard libraries. In other words, when you specify `-nostdlib' you should usually specify `-lgcc' as well. This ensures that you have no unresolved references to internal GNU CC library subroutines. (For example, `__main', used to ensure C++ constructors will be called; *note `collect2': Collect2..) Remove all symbol table and relocation information from the executable. `-static' On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. `-shared' Produce a shared object which can then be linked with other objects to form an executable. Only a few systems support this option. `-symbolic' Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option `-Xlinker -z -Xlinker defs'). Only a few systems support this option. `-Xlinker OPTION' Pass OPTION as an option to the linker. You can use this to supply system-specific linker options which GNU CC does not know how to recognize. If you want to pass an option that takes an argument, you must use `-Xlinker' twice, once for the option and once for the argument. For example, to pass `-assert definitions', you must write `-Xlinker -assert -Xlinker definitions'. It does not work to write `-Xlinker "-assert definitions"', because this passes the entire string as a single argument, which is not what the linker expects. `-Wl,OPTION' Pass OPTION as an option to the linker. If OPTION contains commas, it is split into multiple options at the commas. `-u SYMBOL' Pretend the symbol SYMBOL is undefined, to force linking of library modules to define it. You can use `-u' multiple times with different symbols to force loading of additional library modules. File: gcc.info, Node: Directory Options, Next: Target Options, Prev: Link Options, Up: Invoking GCC Options for Directory Search ============================ These options specify directories to search for header files, for libraries and for parts of the compiler: `-IDIR' Append directory DIR to the list of directories searched for include files. `-I-' Any directories you specify with `-I' options before the `-I-' option are searched only for the case of `#include "FILE"'; they are not searched for `#include '. If additional directories are specified with `-I' options after the `-I-', these directories are searched for all `#include' directives. (Ordinarily *all* `-I' directories are used this way.) In addition, the `-I-' option inhibits the use of the current directory (where the current input file came from) as the first search directory for `#include "FILE"'. There is no way to override this effect of `-I-'. With `-I.' you can specify searching the directory which was current when the compiler was invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory. `-I-' does not inhibit the use of the standard system directories for header files. Thus, `-I-' and `-nostdinc' are independent. `-LDIR' Add directory DIR to the list of directories to be searched for `-l'. `-BPREFIX' This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. The compiler driver program runs one or more of the subprograms `cpp', `cc1', `as' and `ld'. It tries PREFIX as a prefix for each program it tries to run, both with and without `MACHINE/VERSION/' (*note Target Options::.). For each subprogram to be run, the compiler driver first tries the `-B' prefix, if any. If that name is not found, or if `-B' was not specified, the driver tries two standard prefixes, which are `/usr/lib/gcc/' and `/usr/local/lib/gcc-lib/'. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your `PATH' environment variable. `-B' prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into `-L' options for the linker. They also apply to includes files in the preprocessor, because the compiler translates these options into `-isystem' options for the preprocessor. In this case, the compiler appends `include' to the prefix. The run-time support file `libgcc.a' can also be searched for using the `-B' prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Another way to specify a prefix much like the `-B' prefix is to use the environment variable `GCC_EXEC_PREFIX'. *Note Environment Variables::. File: gcc.info, Node: Target Options, Next: Submodel Options, Prev: Directory Options, Up: Invoking GCC Specifying Target Machine and Compiler Version ============================================== By default, GNU CC compiles code for the same type of machine that you are using. However, it can also be installed as a cross-compiler, to compile for some other type of machine. In fact, several different configurations of GNU CC, for different target machines, can be installed side by side. Then you specify which one to use with the `-b' option. In addition, older and newer versions of GNU CC can be installed side by side. One of them (probably the newest) will be the default, but you may sometimes wish to use another. `-b MACHINE' The argument MACHINE specifies the target machine for compilation. This is useful when you have installed GNU CC as a cross-compiler. The value to use for MACHINE is the same as was specified as the machine type when configuring GNU CC as a cross-compiler. For example, if a cross-compiler was configured with `configure i386v', meaning to compile for an 80386 running System V, then you would specify `-b i386v' to run that cross compiler. When you do not specify `-b', it normally means to compile for the same type of machine that you are using. `-V VERSION' The argument VERSION specifies which version of GNU CC to run. This is useful when multiple versions are installed. For example, VERSION might be `2.0', meaning to run GNU CC version 2.0. The default version, when you do not specify `-V', is controlled by the way GNU CC is installed. Normally, it will be a version that is recommended for general use. The `-b' and `-V' options actually work by controlling part of the file name used for the executable files and libraries used for compilation. A given version of GNU CC, for a given target machine, is normally kept in the directory `/usr/local/lib/gcc-lib/MACHINE/VERSION'. Thus, sites can customize the effect of `-b' or `-V' either by changing the names of these directories or adding alternate names (or symbolic links). If in directory `/usr/local/lib/gcc-lib/' the file `80386' is a link to the file `i386v', then `-b 80386' becomes an alias for `-b i386v'. In one respect, the `-b' or `-V' do not completely change to a different compiler: the top-level driver program `gcc' that you originally invoked continues to run and invoke the other executables (preprocessor, compiler per se, assembler and linker) that do the real work. However, since no real work is done in the driver program, it usually does not matter that the driver program in use is not the one for the specified target and version. The only way that the driver program depends on the target machine is in the parsing and handling of special machine-specific options. However, this is controlled by a file which is found, along with the other executables, in the directory for the specified version and target machine. As a result, a single installed driver program adapts to any specified target machine and compiler version. The driver program executable does control one significant thing, however: the default version and target machine. Therefore, you can install different instances of the driver program, compiled for different targets or versions, under different names. For example, if the driver for version 2.0 is installed as `ogcc' and that for version 2.1 is installed as `gcc', then the command `gcc' will use version 2.1 by default, while `ogcc' will use 2.0 by default. However, you can choose either version with either command with the `-V' option. File: gcc.info, Node: Submodel Options, Next: Code Gen Options, Prev: Target Options, Up: Invoking GCC Hardware Models and Configurations ================================== Earlier we discussed the standard option `-b' which chooses among different installed compilers for completely different target machines, such as Vax vs. 68000 vs. 80386. In addition, each of these target machine types can have its own special options, starting with `-m', to choose among various hardware models or configurations--for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified. Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform. These options are defined by the macro `TARGET_SWITCHES' in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults. * Menu: * M680x0 Options:: * VAX Options:: * SPARC Options:: * Convex Options:: * AMD29K Options:: * ARM Options:: * M88K Options:: * RS/6000 and PowerPC Options:: * RT Options:: * MIPS Options:: * i386 Options:: * HPPA Options:: * Intel 960 Options:: * DEC Alpha Options:: * Clipper Options:: * H8/300 Options:: * System V Options:: File: gcc.info, Node: M680x0 Options, Next: VAX Options, Up: Submodel Options M680x0 Options -------------- These are the `-m' options defined for the 68000 series. The default values for these options depends on which style of 68000 was selected when the compiler was configured; the defaults for the most common choices are given below. `-m68000' `-mc68000' Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. `-m68020' `-mc68020' Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. `-m68881' Generate output containing 68881 instructions for floating point. This is the default for most 68020 systems unless `-nfp' was specified when the compiler was configured. `-m68030' Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. `-m68040' Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. If your 68040 does not have code to emulate those instructions, use `-m68040'. `-m68020-40' Generate output for a 68040, without using any of the new instructions. This results in code which can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. `-mfpa' Generate output containing Sun FPA instructions for floating point. `-msoft-float' Generate output containing library calls for floating point. *Warning:* the requisite libraries are not part of GNU CC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. `-mshort' Consider type `int' to be 16 bits wide, like `short int'. `-mnobitfield' Do not use the bit-field instructions. The `-m68000' option implies `-mnobitfield'. `-mbitfield' Do use the bit-field instructions. The `-m68020' option implies `-mbitfield'. This is the default if you use a configuration designed for a 68020. `-mrtd' Use a different function-calling convention, in which functions that take a fixed number of arguments return with the `rtd' instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including `printf'); otherwise incorrect code will be generated for calls to those functions. In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) The `rtd' instruction is supported by the 68010 and 68020 processors, but not by the 68000. File: gcc.info, Node: VAX Options, Next: SPARC Options, Prev: M680x0 Options, Up: Submodel Options VAX Options ----------- These `-m' options are defined for the Vax: `-munix' Do not output certain jump instructions (`aobleq' and so on) that the Unix assembler for the Vax cannot handle across long ranges. `-mgnu' Do output those jump instructions, on the assumption that you will assemble with the GNU assembler. `-mg' Output code for g-format floating point numbers instead of d-format. File: gcc.info, Node: SPARC Options, Next: Convex Options, Prev: VAX Options, Up: Submodel Options SPARC Options ------------- These `-m' switches are supported on the SPARC: `-mno-app-regs' `-mapp-regs' Specify `-mapp-regs' to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. This is the default. To be fully SVR4 ABI compliant at the cost of some performance loss, specify `-mno-app-regs'. You should compile libraries and system software with this option. `-mfpu' `-mhard-float' Generate output containing floating point instructions. This is the default. `-mno-fpu' `-msoft-float' Generate output containing library calls for floating point. *Warning:* there is no GNU floating-point library for SPARC. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. `-msoft-float' changes the calling convention in the output file; therefore, it is only useful if you compile *all* of a program with this option. In particular, you need to compile `libgcc.a', the library that comes with GNU CC, with `-msoft-float' in order for this to work. `-mhard-quad-float' Generate output containing quad-word (long double) floating point instructions. `-msoft-quad-float' Generate output containing library calls for quad-word (long double) floating point instructions. The functions called are those specified in the SPARC ABI. This is the default. As of this writing, there are no sparc implementations that have hardware support for the quad-word floating point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the `-msoft-quad-float' option is the default. `-mno-epilogue' `-mepilogue' With `-mepilogue' (the default), the compiler always emits code for function exit at the end of each function. Any function exit in the middle of the function (such as a return statement in C) will generate a jump to the exit code at the end of the function. With `-mno-epilogue', the compiler tries to emit exit code inline at every function exit. `-mno-flat' `-mflat' With `-mflat', the compiler does not generate save/restore instructions and will use a "flat" or single register window calling convention. This model uses %i7 as the frame pointer and is compatible with the normal register window model. Code from either may be intermixed although debugger support is still incomplete. The local registers and the input registers (0-5) are still treated as "call saved" registers and will be saved on the stack as necessary. With `-mno-flat' (the default), the compiler emits save/restore instructions (except for leaf functions) and is the normal mode of operation. `-mno-unaligned-doubles' `-munaligned-doubles' Assume that doubles have 8 byte alignment. This is the default. With `-munaligned-doubles', GNU CC assumes that doubles have 8 byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4 byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating point code. `-mv8' `-msparclite' These two options select variations on the SPARC architecture. By default (unless specifically configured for the Fujitsu SPARClite), GCC generates code for the v7 variant of the SPARC architecture. `-mv8' will give you SPARC v8 code. The only difference from v7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC v8 but not in SPARC v7. `-msparclite' will give you SPARClite code. This adds the integer multiply, integer divide step and scan (`ffs') instructions which exist in SPARClite but not in SPARC v7. `-mcypress' `-msupersparc' These two options select the processor for which the code is optimised. With `-mcypress' (the default), the compiler optimizes code for the Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. This is also apropriate for the older SparcStation 1, 2, IPX etc. With `-msupersparc' the compiler optimizes code for the SuperSparc cpu, as used in the SparcStation 10, 1000 and 2000 series. This flag also enables use of the full SPARC v8 instruction set. In a future version of GCC, these options will very likely be renamed to `-mcpu=cypress' and `-mcpu=supersparc'. These `-m' switches are supported in addition to the above on SPARC V9 processors: `-mmedlow' Generate code for the Medium/Low code model: assume a 32 bit address space. Programs are statically linked, PIC is not supported. Pointers are still 64 bits. It is very likely that a future version of GCC will rename this option. `-mmedany' Generate code for the Medium/Anywhere code model: assume a 32 bit text segment starting at offset 0, and a 32 bit data segment starting anywhere (determined at link time). Programs are statically linked, PIC is not supported. Pointers are still 64 bits. It is very likely that a future version of GCC will rename this option. `-mint64' Types long and int are 64 bits. `-mlong32' Types long and int are 32 bits. `-mlong64' `-mint32' Type long is 64 bits, and type int is 32 bits. `-mstack-bias' `-mno-stack-bias' With `-mstack-bias', GNU CC assumes that the stack pointer, and frame pointer if present, are offset by -2047 which must be added back when making stack frame references. Otherwise, assume no such offset is present.