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This is Info file gcc.info, produced by Makeinfo-1.49 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Copyright (C) 1988, 1989, 1992 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: 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. `-c' `-S' `-E' 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' This special case of the `-l' option is what you need to do when you link an Objective C program. `-nostdlib' Don't use the standard system libraries and startup files when linking. Only the files you specify will be passed to the linker. `-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 <FILE>'. 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 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. 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'. It follows that sites can customize the effect of `-b' or `-V' either by changing the names of these directories or adding alternate names (or symbolic links). Thus, if `/usr/local/lib/gcc-lib/80386' is a link to `/usr/local/lib/gcc-lib/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 Specifying 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:: * M88K Options:: * RS/6000 Options:: * RT Options:: * MIPS Options:: * i386 Options:: * HPPA Options:: * Intel 960 Options:: * DEC Alpha 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. `-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. `-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. `-m68000' implies `-mnobitfield'. `-mbitfield' Do use the bit-field instructions. `-m68020' implies `-mbitfield'. This is the default if you use the unmodified sources configured 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: `-mforce-align' Make sure all objects of type `double' are 8-byte aligned in memory and use double-word instructions to reference them. `-mno-epilogue' Generate separate return instructions for `return' statements. This has both advantages and disadvantages; I don't recall what they are. File: gcc.info, Node: Convex Options, Next: AMD29K Options, Prev: SPARC Options, Up: Submodel Options Convex Options -------------- These `-m' options are defined for the Convex: `-mc1' Generate output for a C1. This is the default when the compiler is configured for a C1. `-mc2' Generate output for a C2. This is the default when the compiler is configured for a C2. `-margcount' Generate code which puts an argument count in the word preceding each argument list. Some nonportable Convex and Vax programs need this word. (Debuggers don't, except for functions with variable-length argument lists; this info is in the symbol table.) `-mnoargcount' Omit the argument count word. This is the default if you use the unmodified sources. File: gcc.info, Node: AMD29K Options, Next: M88K Options, Prev: Convex Options, Up: Submodel Options AMD29K Options -------------- These `-m' options are defined for the AMD Am29000: `-mdw' Generate code that assumes the `DW' bit is set, i.e., that byte and halfword operations are directly supported by the hardware. This is the default. `-mnodw' Generate code that assumes the `DW' bit is not set. `-mbw' Generate code that assumes the system supports byte and halfword write operations. This is the default. `-mnbw' Generate code that assumes the systems does not support byte and halfword write operations. `-mnbw' implies `-mnodw'. `-msmall' Use a small memory model that assumes that all function addresses are either within a single 256 KB segment or at an absolute address of less than 256K. This allows the `call' instruction to be used instead of a `const', `consth', `calli' sequence. `-mlarge' Do not assume that the `call' instruction can be used; this is the default. `-m29050' Generate code for the Am29050. `-m29000' Generate code for the Am29000. This is the default. `-mkernel-registers' Generate references to registers `gr64-gr95' instead of `gr96-gr127'. This option can be used when compiling kernel code that wants a set of global registers disjoint from that used by user-mode code. Note that when this option is used, register names in `-f' flags must use the normal, user-mode, names. `-muser-registers' Use the normal set of global registers, `gr96-gr127'. This is the default. `-mstack-check' Insert a call to `__msp_check' after each stack adjustment. This is often used for kernel code. File: gcc.info, Node: M88K Options, Next: RS/6000 Options, Prev: AMD29K Options, Up: Submodel Options M88K Options ------------ These `-m' options are defined for Motorola 88K architectures: `-m88000' Generate code that works well on both the m88100 and the m88110. `-m88100' Generate code that works best for the m88100, but that also runs on the m88110. `-m88110' Generate code that works best for the m88110, and may not run on the m88100. `-midentify-revision' Include an `ident' directive in the assembler output recording the source file name, compiler name and version, timestamp, and compilation flags used. `-mno-underscores' In assembler output, emit symbol names without adding an underscore character at the beginning of each name. The default is to use an underscore as prefix on each name. `-mocs-debug-info' `-mno-ocs-debug-info' Include (or omit) additional debugging information (about registers used in each stack frame) as specified in the 88open Object Compatibility Standard, "OCS". This extra information allows debugging of code that has had the frame pointer eliminated. The default for DG/UX, SVr4, and Delta 88 SVr3.2 is to include this information; other 88k configurations omit this information by default. `-mocs-frame-position' When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the canonical frame address, which is the stack pointer (register 31) on entry to the function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use `-mocs-frame-position'; other 88k configurations have the default `-mno-ocs-frame-position'. `-mno-ocs-frame-position' When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the frame pointer register (register 30). When this option is in effect, the frame pointer is not eliminated when debugging information is selected by the -g switch. `-moptimize-arg-area' `-mno-optimize-arg-area' Control how to store function arguments in stack frames. `-moptimize-arg-area' saves space, but conflicts with the 88open specifications. `-mno-optimize-arg-area' conforms to the 88open standards. By default GNU CC does not optimize the argument area. `-mshort-data-NUM' Generate smaller data references by making them relative to `r0', which allows loading a value using a single instruction (rather than the usual two). You control which data references are affected by specifying NUM with this option. For example, if you specify `-mshort-data-512', then the data references affected are those involving displacements of less than 512 bytes. `-mshort-data-NUM' is not effective for NUM greater than 64K. `-mserialize-volatile' `-mno-serialize-volatile' Do, or don't, generate code to guarantee sequential consistency of volatile memory references. GNU CC always guarantees consistency by default, for the preferred processor submodel. How this is done depends on the submodel. The m88100 processor does not reorder memory references and so always provides sequential consistency. If you use `-m88100', GNU CC does not generate any special instructions for sequential consistency. The order of memory references made by the m88110 processor does not always match the order of the instructions requesting those references. In particular, a load instruction may execute before a preceding store instruction. Such reordering violates sequential consistency of volatile memory references, when there are multiple processors. When you use `-m88000' or `-m88110', GNU CC generates special instructions when appropriate, to force execution in the proper order. The extra code generated to guarantee consistency may affect the performance of your application. If you know that you can safely forgo this guarantee, you may use `-mno-serialize-volatile'. If you use `-m88100' but require sequential consistency when running on the m88110 processor, you should use `-mserialize-volatile'. `-msvr4' `-msvr3' Turn on (`-msvr4') or off (`-msvr3') compiler extensions related to System V release 4 (SVr4). This controls the following: 1. Which variant of the assembler syntax to emit (which you can select independently using `-mversion-03.00'). 2. `-msvr4' makes the C preprocessor recognize `#pragma weak' that is used on System V release 4. 3. `-msvr4' makes GNU CC issue additional declaration directives used in SVr4. `-msvr3' is the default for all m88K configurations except the SVr4 configuration. `-mversion-03.00' In the DG/UX configuration, there are two flavors of SVr4. This option modifies `-msvr4' to select whether the hybrid-COFF or real-ELF flavor is used. All other configurations ignore this option. `-mno-check-zero-division' `-mcheck-zero-division' Early models of the 88K architecture had problems with division by zero; in particular, many of them didn't trap. Use these options to avoid including (or to include explicitly) additional code to detect division by zero and signal an exception. All GNU CC configurations for the 88K use `-mcheck-zero-division' by default. `-muse-div-instruction' Do not emit code to check both the divisor and dividend when doing signed integer division to see if either is negative, and adjust the signs so the divide is done using non-negative numbers. Instead, rely on the operating system to calculate the correct value when the `div' instruction traps. This results in different behavior when the most negative number is divided by -1, but is useful when most or all signed integer divisions are done with positive numbers. `-mtrap-large-shift' `-mhandle-large-shift' Include code to detect bit-shifts of more than 31 bits; respectively, trap such shifts or emit code to handle them properly. By default GNU CC makes no special provision for large bit shifts. `-mwarn-passed-structs' Warn when a function passes a struct as an argument or result. Structure-passing conventions have changed during the evolution of the C language, and are often the source of portability problems. By default, GNU CC issues no such warning. File: gcc.info, Node: RS/6000 Options, Next: RT Options, Prev: M88K Options, Up: Submodel Options IBM RS/6000 Options ------------------- Only one pair of `-m' options is defined for the IBM RS/6000: `-mfp-in-toc' `-mno-fp-in-toc' Control whether or not floating-point constants go in the Table of Contents (TOC), a table of all global variable and function addresses. By default GNU CC puts floating-point constants there; if the TOC overflows, `-mno-fp-in-toc' will reduce the size of the TOC, which may avoid the overflow. File: gcc.info, Node: RT Options, Next: MIPS Options, Prev: RS/6000 Options, Up: Submodel Options IBM RT Options -------------- These `-m' options are defined for the IBM RT PC: `-min-line-mul' Use an in-line code sequence for integer multiplies. This is the default. `-mcall-lib-mul' Call `lmul$$' for integer multiples. `-mfull-fp-blocks' Generate full-size floating point data blocks, including the minimum amount of scratch space recommended by IBM. This is the default. `-mminimum-fp-blocks' Do not include extra scratch space in floating point data blocks. This results in smaller code, but slower execution, since scratch space must be allocated dynamically. `-mfp-arg-in-fpregs' Use a calling sequence incompatible with the IBM calling convention in which floating point arguments are passed in floating point registers. Note that `varargs.h' and `stdargs.h' will not work with floating point operands if this option is specified. `-mfp-arg-in-gregs' Use the normal calling convention for floating point arguments. This is the default. `-mhc-struct-return' Return structures of more than one word in memory, rather than in a register. This provides compatibility with the MetaWare HighC (hc) compiler. Use `-fpcc-struct-return' for compatibility with the Portable C Compiler (pcc). `-mnohc-struct-return' Return some structures of more than one word in registers, when convenient. This is the default. For compatibility with the IBM-supplied compilers, use either `-fpcc-struct-return' or `-mhc-struct-return'. File: gcc.info, Node: MIPS Options, Next: i386 Options, Prev: RT Options, Up: Submodel Options MIPS Options ------------ These `-m' options are defined for the MIPS family of computers: `-mcpu=CPU TYPE' Assume the defaults for the machine type CPU TYPE when scheduling instructions. The default CPU TYPE is `default', which picks the longest cycles times for any of the machines, in order that the code run at reasonable rates on all MIPS cpu's. Other choices for CPU TYPE are `r2000', `r3000', `r4000', and `r6000'. While picking a specific CPU TYPE will schedule things appropriately for that particular chip, the compiler will not generate any code that does not meet level 1 of the MIPS ISA (instruction set architecture) without the `-mips2' or `-mips3' switches being used. `-mips2' Issue instructions from level 2 of the MIPS ISA (branch likely, square root instructions). The `-mcpu=r4000' or `-mcpu=r6000' switch must be used in conjunction with `-mips2'. `-mips3' Issue instructions from level 3 of the MIPS ISA (64 bit instructions). You must use the `-mcpu=r4000' switch along with `-mips3'. `-mint64' `-mlong64' `-mlonglong128' These options don't work at present. `-mmips-as' Generate code for the MIPS assembler, and invoke `mips-tfile' to add normal debug information. This is the default for all platforms except for the OSF/1 reference platform, using the OSF/rose object format. If the either of the `-gstabs' or `-gstabs+' switches are used, the `mips-tfile' program will encapsulate the stabs within MIPS ECOFF. `-mgas' Generate code for the GNU assembler. This is the default on the OSF/1 reference platform, using the OSF/rose object format. `-mrnames' `-mno-rnames' The `-mrnames' switch says to output code using the MIPS software names for the registers, instead of the hardware names (ie, A0 instead of $4). The GNU assembler does not support the `-mrnames' switch, and the MIPS assembler will be instructed to run the MIPS C preprocessor over the source file. The `-mno-rnames' switch is default. `-mgpopt' `-mno-gpopt' The `-mgpopt' switch says to write all of the data declarations before the instructions in the text section, this allows the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected. `-mstats' `-mno-stats' For each non-inline function processed, the `-mstats' switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.). `-mmemcpy' `-mno-memcpy' The `-mmemcpy' switch makes all block moves call the appropriate string function (`memcpy' or `bcopy') instead of possibly generating inline code. `-mmips-tfile' `-mno-mips-tfile' The `-mno-mips-tfile' switch causes the compiler not postprocess the object file with the `mips-tfile' program, after the MIPS assembler has generated it to add debug support. If `mips-tfile' is not run, then no local variables will be available to the debugger. In addition, `stage2' and `stage3' objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. The `-mno-mips-tfile' switch should only be used when there are bugs in the `mips-tfile' program that prevents compilation. `-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. `-mhard-float' Generate output containing floating point instructions. This is the default if you use the unmodified sources. `-mfp64' Assume that the FR bit in the status word is on, and that there are 32 64-bit floating point registers, instead of 32 32-bit floating point registers. You must also specify the `-mcpu=r4000' and `-mips3' switches. `-mfp32' Assume that there are 32 32-bit floating point registers. This is the default. `-mabicalls' `-mno-abicalls' Emit the `.abicalls', `.cpload', and `.cprestore' pseudo operations that some System V.4 ports use for position independent code. `-mhalf-pic' `-mno-half-pic' Put pointers to extern references into the data section and load them up, rather than put the references in the text section. These options do not work at present. `-G NUM' Put global and static items less than or equal to NUM bytes into the small data or bss sections instead of the normal data or bss section. This allows the assembler to emit one word memory reference instructions based on the global pointer (GP or $28), instead of the normal two words used. By default, NUM is 8 when the MIPS assembler is used, and 0 when the GNU assembler is used. The `-G NUM' switch is also passed to the assembler and linker. All modules should be compiled with the same `-G NUM' value. `-nocpp' Tell the MIPS assembler to not run it's preprocessor over user assembler files (with a `.s' suffix) when assembling them. 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. File: gcc.info, Node: i386 Options, Next: HPPA Options, Prev: MIPS Options, Up: Submodel Options Intel 386 Options ----------------- These `-m' options are defined for the i386 family of computers: `-m486' `-mno-486' Control whether or not code is optimized for a 486 instead of an 386. Code generated for an 486 will run on a 386 and vice versa. `-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. On machines where a function returns floating point results in the 80387 register stack, some floating point opcodes may be emitted even if `-msoft-float' is used. `-mno-fp-ret-in-387' Don't use the FPU registers for return values of functions. The usual calling convention has functions return values of types `float' and `double' in an FPU register, even if there is no FPU. The idea is that the operating system should emulate an FPU. The option `-mno-fp-ret-in-387' causes such values to be returned in ordinary CPU registers instead. File: gcc.info, Node: HPPA Options, Next: Intel 960 Options, Prev: i386 Options, Up: Submodel Options HPPA Options ------------ This `-m' option is defined for the HPPA family of computers: `-mno-bss' Disable the use of the BSS section. This may be necessary with older versions of pa-gas. It is highly recommended that you pick up a new version of pa-gas from `jaguar.cs.utah.edu'. `-mpa-risc-1-0' Generate code for a PA 1.0 processor. `-mpa-risc-1-1' Generate code for a PA 1.1 processor. `-mkernel' Generate code which is suitable for use in kernels. Specifically, avoid `add' instructions in which one of the arguments is the DP register; generate `addil' instructions instead. This avoids a rather serious bug in the HP-UX linker. `-mshared-libs' Generate code that can be linked against HP-UX shared libraries. This option is not fully function yet, and is not on by default for any PA target. `-mno-shared-libs' Don't generate code that will be linked against shared libraries. This is the default for all PA targets. `-mlong-calls' Generate code which allows calls to functions greater than 256K away from the caller when the caller and callee are in the same source file. Do not turn this option on unless code refuses to link with "branch out of range errors" from the linker. File: gcc.info, Node: Intel 960 Options, Next: DEC Alpha Options, Prev: HPPA Options, Up: Submodel Options Intel 960 Options ----------------- These `-m' options are defined for the Intel 960 implementations: `-mCPU TYPE' Assume the defaults for the machine type CPU TYPE for some of the other options, including instruction scheduling, floating point support, and addressing modes. The choices for CPU TYPE are `ka', `kb', `mc', `ca', `cf', `sa', and `sb'. The default is `kb'. `-mnumerics' `-msoft-float' The `-mnumerics' option indicates that the processor does support floating-point instructions. The `-msoft-float' option indicates that floating-point support should not be assumed. `-mleaf-procedures' `-mno-leaf-procedures' Do (or do not) attempt to alter leaf procedures to be callable with the `bal' instruction as well as `call'. This will result in more efficient code for explicit calls when the `bal' instruction can be substituted by the assembler or linker, but less efficient code in other cases, such as calls via function pointers, or using a linker that doesn't support this optimization. `-mtail-call' `-mno-tail-call' Do (or do not) make additional attempts (beyond those of the machine-independent portions of the compiler) to optimize tail-recursive calls into branches. You may not want to do this because the detection of cases where this is not valid is not totally complete. The default is `-mno-tail-call'. `-mcomplex-addr' `-mno-complex-addr' Assume (or do not assume) that the use of a complex addressing mode is a win on this implementation of the i960. Complex addressing modes may not be worthwhile on the K-series, but they definitely are on the C-series. The default is currently `-mcomplex-addr' for all processors except the CB and CC. `-mcode-align' `-mno-code-align' Align code to 8-byte boundaries for faster fetching (or don't bother). Currently turned on by default for C-series implementations only. `-mic-compat' `-mic2.0-compat' `-mic3.0-compat' Enable compatibility with iC960 v2.0 or v3.0. `-masm-compat' `-mintel-asm' Enable compatibility with the iC960 assembler. `-mstrict-align' `-mno-strict-align' Do not permit (do permit) unaligned accesses. `-mold-align' Enable structure-alignment compatibility with Intel's gcc release version 1.3 (based on gcc 1.37). Currently this is buggy in that `#pragma align 1' is always assumed as well, and cannot be turned off. 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' Use the same convention for returning `struct' and `union' values that is used by the usual C compiler on your system. This convention is less efficient for small structures, and on many machines it fails to be reentrant; but it has the advantage of allowing intercallability between GNU CC-compiled code and PCC-compiled code. `-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' Don't 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 "collect" program and a non-GNU linker. `-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. `-fnonnull-objects' Assume that objects reached through references are not null (C++ only). Normally, GNU C++ makes conservative assumptions about objects reached through references. For example, the compiler must check that `a' is not null in code like the following: obj &a = g (); a.f (2); Checking that references of this sort have non-null values requires extra code, however, and it is unnecessary for many programs. You can use `-fnonnull-objects' to omit the checks for null, if your program doesn't require checking. `-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. `-fpic' If supported for the target machine, generate position-independent code (PIC) suitable for use in a shared library. All addresses will be accessed through a global offset table (GOT). If the GOT size for the linked executable exceeds a machine-specific maximum size, you will get an error message from the linker indicating that `-fpic' does not work; 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.