V10/cmd/gcc/internals-1
File: internals, Node: Top, Next: Copying, Up: (DIR)
Introduction
************
This manual documents how to run, install and port the GNU C compiler, as
well as its new features and incompatibilities, and how to report bugs.
* Menu:
* Copying:: GNU CC General Public License says
how you can copy and share GNU CC.
* Contributors:: People who have contributed to GNU CC.
* Options:: Command options supported by `gcc'.
* Installation:: How to configure, compile and install GNU CC.
* Trouble:: If you have trouble installing GNU CC.
* Incompatibilities:: Incompatibilities of GNU CC.
* Extensions:: GNU extensions to the C language.
* Bugs:: How to report bugs (if you want to get them fixed).
* Portability:: Goals of GNU CC's portability features.
* Interface:: Function-call interface of GNU CC output.
* Passes:: Order of passes, what they do, and what each file is for.
* RTL:: The intermediate representation that most passes work on.
* Machine Desc:: How to write machine description instruction patterns.
* Machine Macros:: How to write the machine description C macros.
File: internals, Node: Copying, Next: Contributors, Prev: Top, Up: Top
GNU CC GENERAL PUBLIC LICENSE
*****************************
(Clarified 11 Feb 1988)
The license agreements of most software companies keep you at the mercy
of those companies. By contrast, our general public license is intended to
give everyone the right to share GNU CC. To make sure that you get the
rights we want you to have, we need to make restrictions that forbid anyone
to deny you these rights or to ask you to surrender the rights. Hence this
license agreement.
Specifically, we want to make sure that you have the right to give away
copies of GNU CC, that you receive source code or else can get it if you
want it, that you can change GNU CC or use pieces of it in new free
programs, and that you know you can do these things.
To make sure that everyone has such rights, we have to forbid you to
deprive anyone else of these rights. For example, if you distribute copies
of GNU CC, you must give the recipients all the rights that you have. You
must make sure that they, too, receive or can get the source code. And you
must tell them their rights.
Also, for our own protection, we must make certain that everyone finds
out that there is no warranty for GNU CC. If GNU CC is modified by someone
else and passed on, we want its recipients to know that what they have is
not what we distributed, so that any problems introduced by others will not
reflect on our reputation.
Therefore we (Richard Stallman and the Free Software Foundation, Inc.)
make the following terms which say what you must do to be allowed to
distribute or change GNU CC.
COPYING POLICIES
================
1. You may copy and distribute verbatim copies of GNU CC source code as you
receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy a valid copyright notice
``Copyright (C) 1988 Free Software Foundation, Inc.'' (or with
whatever year is appropriate); keep intact the notices on all files
that refer to this License Agreement and to the absence of any
warranty; and give any other recipients of the GNU CC program a copy
of this License Agreement along with the program. You may charge a
distribution fee for the physical act of transferring a copy.
2. You may modify your copy or copies of GNU CC or any portion of it, and
copy and distribute such modifications under the terms of Paragraph 1
above, provided that you also do the following:
* cause the modified files to carry prominent notices stating that
you changed the files and the date of any change; and
* cause the whole of any work that you distribute or publish, that
in whole or in part contains or is a derivative of GNU CC or any
part thereof, to be licensed at no charge to all third parties on
terms identical to those contained in this License Agreement
(except that you may choose to grant more extensive warranty
protection to some or all third parties, at your option).
* You may charge a distribution fee for the physical act of
transferring a copy, and you may at your option offer warranty
protection in exchange for a fee.
Mere aggregation of another unrelated program with this program (or
its derivative) on a volume of a storage or distribution medium does
not bring the other program under the scope of these terms.
3. You may copy and distribute GNU CC (or a portion or derivative of it,
under Paragraph 2) in object code or executable form under the terms
of Paragraphs 1 and 2 above provided that you also do one of the
following:
* accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of
Paragraphs 1 and 2 above; or,
* accompany it with a written offer, valid for at least three
years, to give any third party free (except for a nominal
shipping charge) a complete machine-readable copy of the
corresponding source code, to be distributed under the terms of
Paragraphs 1 and 2 above; or,
* accompany it with the information you received as to where the
corresponding source code may be obtained. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form alone.)
For an executable file, complete source code means all the source code
for all modules it contains; but, as a special exception, it need not
include source code for modules which are standard libraries that
accompany the operating system on which the executable file runs.
4. You may not copy, sublicense, distribute or transfer GNU CC except as
expressly provided under this License Agreement. Any attempt
otherwise to copy, sublicense, distribute or transfer GNU CC is void
and your rights to use the program under this License agreement shall
be automatically terminated. However, parties who have received
computer software programs from you with this License Agreement will
not have their licenses terminated so long as such parties remain in
full compliance.
5. If you wish to incorporate parts of GNU CC into other free programs
whose distribution conditions are different, write to the Free
Software Foundation at 675 Mass Ave, Cambridge, MA 02139. We have not
yet worked out a simple rule that can be stated here, but we will
often permit this. We will be guided by the two goals of preserving
the free status of all derivatives of our free software and of
promoting the sharing and reuse of software.
Your comments and suggestions about our licensing policies and our software
are welcome! Please contact the Free Software Foundation, Inc., 675 Mass
Ave, Cambridge, MA 02139, or call (617) 876-3296.
NO WARRANTY
===========
BECAUSE GNU CC IS LICENSED FREE OF CHARGE, WE PROVIDE ABSOLUTELY NO
WARRANTY, TO THE EXTENT PERMITTED BY APPLICABLE STATE LAW. EXCEPT WHEN
OTHERWISE STATED IN WRITING, FREE SOFTWARE FOUNDATION, INC, RICHARD M.
STALLMAN AND/OR OTHER PARTIES PROVIDE GNU CC "AS IS" WITHOUT WARRANTY OF
ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF GNU CC IS WITH YOU.
SHOULD GNU CC PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW WILL RICHARD M. STALLMAN,
THE FREE SOFTWARE FOUNDATION, INC., AND/OR ANY OTHER PARTY WHO MAY MODIFY
AND REDISTRIBUTE GNU CC AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY LOST PROFITS, LOST MONIES, OR OTHER SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE (INCLUDING
BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES
SUSTAINED BY THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
OTHER PROGRAMS) GNU CC, EVEN IF YOU HAVE BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES, OR FOR ANY CLAIM BY ANY OTHER PARTY.
File: internals, Node: Contributors, Next: Options, Prev: Copying, Up: Top
Contributors to GNU CC
**********************
In addition to Richard Stallman, several people have written parts of GNU CC.
* The idea of using RTL and some of the optimization ideas came from the
U. of Arizona Portable Optimizer, written by Jack Davidson and
Christopher Fraser. See ``Register Allocation and Exhaustive Peephole
Optimization'', Software Practice and Experience 14 (9), Sept. 1984,
857-866.
* Paul Rubin wrote most of the preprocessor.
* Leonard Tower wrote parts of the parser, RTL generator, RTL
definitions, and of the Vax machine description.
* Ted Lemon wrote parts of the RTL reader and printer.
* Nobuyuki Hikichi of Software Research Associates, Tokyo, contributed
the support for the SONY NEWS machine.
* Charles LaBrec contributed the support for the Integrated Solutions
68020 system.
* Michael Tiemann of MCC wrote the description of the National
Semiconductor 32000 series cpu, with some contributions from Jan Stein
of the Chalmers Computer Club. Tiemann also wrote the code for inline
function integration.
* Robert Brown implemented the support for Encore 32000 systems.
* Michael Kashtan of SRI adapted GNU CC to the Vomit-Making System.
* Alex Crain provided changes for the 3b1.
* Chris Hanson and another person who should remind me of his name
assisted in making GNU CC work on HP-UX for the 9000 series 300.
File: internals, Node: Options, Next: Installation, Prev: Contributors, Up: Top
GNU CC Command Options
**********************
The GNU C compiler uses a command syntax much like the Unix C compiler.
The `gcc' program accepts options and file names as operands. Multiple
single-letter options may *not* be grouped: `-dr' is very different from
`-d -r'.
When you invoke GNU CC, it normally does preprocessing, compilation,
assembly and linking. File names which end in `.c' are taken as C source
to be preprocessed and compiled; compiler output files plus any input files
with names ending in `.s' are assembled; then the resulting object files,
plus any other input files, are linked together to produce an executable.
Command options allow you to stop this process at an intermediate stage.
For example, the `-c' option says not to run the linker. Then the output
consists of object files output by the assembler.
Other command options are passed on to one stage. Some options control the
preprocessor and others the compiler itself. Yet other options control the
assembler and linker; these are not documented here because the GNU
assembler and linker are not yet released.
Here are the options to control the overall compilation process, including
those that say whether to link, whether to assemble, and so on.
`-o FILE'
Place output in file FILE. This applies regardless to whatever sort
of output is being produced, whether it be an executable file, an
object file, an assembler file or preprocessed C code.
If `-o' is not specified, the default is to put an executable file in
`a.out', the object file `SOURCE.c' in `SOURCE.o', an assembler file
in `SOURCE.s', and preprocessed C on standard output.
`-c'
Compile or assemble the source files, but do not link. Produce object
files with names made by replacing `.c' or `.s' with `.o' at the end
of the input file names. Do nothing at all for object files specified
as input.
`-S'
Compile into assembler code but do not assemble. The assembler output
file name is made by replacing `.c' with `.s' at the end of the input
file name. Do nothing at all for assembler source files or object
files specified as input.
`-E'
Run only the C preprocessor. Preprocess all the C source files
specified and output the results to standard output.
`-v'
Compiler driver program prints the commands it executes as it runs the
preprocessor, compiler proper, assembler and linker. Some of these
are directed to print their own version numbers.
`-BPREFIX'
Compiler driver program tries PREFIX as a prefix for each program it
tries to run. These programs are `cpp', `cc1', `as' and `ld'.
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-'. 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.
The run-time support file `gnulib' is also 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. Most of the time, on most
machines, you can do without it.
These options control the details of C compilation itself.
`-ansi'
Support all ANSI standard C programs.
This turns off certain features of GNU C that are incompatible with
ANSI C, such as the `asm', `inline' and `typeof' keywords, and
predefined macros such as `unix' and `vax' that identify the type of
system you are using. It also enables the undesirable and rarely used
ANSI trigraph feature.
The `-ansi' option does not cause non-ANSI programs to be rejected
gratuitously. For that, `-pedantic' is required in addition to `-ansi'.
The macro `__STRICT_ANSI__' is predefined when the `-ansi' option is
used. Some header files may notice this macro and refrain from
declaring certain functions or defining certain macros that the ANSI
standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.
`-traditional'
Attempt to support some aspects of traditional C compilers.
Specifically:
* All `extern' declarations take effect globally even if they are
written inside of a function definition. This includes implicit
declarations of functions.
* The keywords `typeof', `inline', `signed', `const' and `volatile'
are not recognized.
* Comparisons between pointers and integers are always allowed.
* Integer types `unsigned short' and `unsigned char' promote to
`unsigned int'.
* In the preprocessor, comments convert to nothing at all, rather
than to a space. This allows traditional token concatenation.
* In the preprocessor, single and double quote characters are
ignored when scanning macro definitions, so that macro arguments
can be replaced even within a string or character constant.
Quote characters are also ignored when skipping text inside a
failing conditional directive.
`-O'
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', only variables declared `register' are allocated 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.
Some of the `-f' options described below turn specific kinds of
optimization on or off.
`-g'
Produce debugging information in DBX format.
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.
`-gg'
Produce debugging information in GDB's own format. This requires the
GNU assembler and linker in order to work.
`-w'
Inhibit all warning messages.
`-W'
Print extra warning messages for these events:
* An automatic variable is used without first being initialized.
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing. They occur only for variables that are
candidates for register allocation. Therefore, they do not occur
for a variable that is declared `volatile', or whose address is
taken, or whose size is other than 1, 2, 4 or 8 bytes. Also,
they do not occur for structures, unions or arrays, even when
they are in registers.
Note that there may be no warning about a variable that is used
only to compute a value that itself is never used, because such
computations may be deleted by the flow analysis pass before the
warnings are printed.
These warnings are made optional because GNU CC is not smart
enough to see all the reasons why the code might be correct
despite appearing to have an error. Here is one example of how
this can happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of `y' is always 1, 2 or 3, then `x' is always
initialized, but GNU CC doesn't know this. Here is another
common case:
{
int save_y;
if (change_y) save_y = y, y = new_y;
...
if (change_y) y = save_y;
}
This has no bug because `x' is used only if it is set.
* A nonvolatile automatic variable might be changed by a call to
`longjmp'. These warnings as well are possible only in
optimizing compilation.
The compiler sees only the calls to `setjmp'. It cannot know
where `longjmp' will be called; in fact, a signal handler could
call it at any point in the code. As a result, you may get a
warning even when there is in fact no problem because `longjmp'
cannot in fact be called at the place which would cause a problem.
* A function can return either with or without a value. (Falling
off the end of the function body is considered returning without
a value.) For example, this function would inspire such a warning:
foo (a)
{
if (a > 0)
return a;
}
Spurious warnings can occur because GNU CC does not realize that
certain functions (including `abort' and `longjmp') will never
return.
In the future, other useful warnings may also be enabled by this option.
`-Wimplicit'
Warn whenever a function is implicitly declared.
`-Wreturn-type'
Warn whenever a function is defined with a return-type that defaults
to `int'. Also warn about any `return' statement with no return-value
in a function whose return-type is not `void'.
`-Wcomment'
Warn whenever a comment-start sequence `/*' appears in a comment.
`-Wall'
All of the above `-W' options combined.
`-p'
Generate extra code to write profile information suitable for the
analysis program `prof'.
`-pg'
Generate extra code to write profile information suitable for the
analysis program `gprof'.
`-lLIBRARY'
Search a standard list of directories for a library named LIBRARY,
which is actually a file named `libLIBRARY.a'. The linker 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
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 an `-l' option and the full file name of the file
that is found is syntactic and the fact that several directories are
searched.
`-LDIR'
Add directory DIR to the list of directories to be searched for `-l'.
`-nostdlib'
Don't use the standard system libraries and startup files when
linking. Only the files you specify (plus `gnulib') will be passed to
the linker.
`-mMACHINESPEC'
Machine-dependent option specifying something about the type of target
machine. 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.
These are the `-m' options defined in the 68000 machine description:
`-m68020'
Generate output for a 68020 (rather than a 68000). This is the
default if you use the unmodified sources.
`-m68000'
Generate output for a 68000 (rather than a 68020).
`-m68881'
Generate output containing 68881 instructions for floating point.
This is the default if you use the unmodified sources.
`-msoft-float'
Generate output containing library calls for floating point.
`-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.
`-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.
These `-m' options are defined in the Vax machine description:
`-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.
`-fFLAG'
Specify machine-independent flags. These are the flags:
`-ffloat-store'
Do not store floating-point variables in registers. This
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-asm'
Do not recognize `asm', `inline' or `typeof' as a keyword. These
words may then be used as identifiers.
`-fno-defer-pop'
Always pop the arguments to each function call as soon as that
function returns. Normally the compiler (when optimizing) lets
arguments accumulate on the stack for several function calls and
pops them all at once.
`-fcombine-regs'
Allow the combine pass to combine an instruction that copies one
register into another. This might or might not produce better
code when used in addition to `-O'. I am interested in hearing
about the difference this makes.
`-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, 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::.
`-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.
`-fwritable-strings'
Store string constants in the writable data segment and don't
uniquize them. This is for compatibility with old programs which
assume they can write into string constants. Writing into string
constants is a very bad idea; ``constants'' should be constant.
`-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.
`-fvolatile'
Consider all memory references through pointers to be volatile.
`-funsigned-char'
Let the type `char' be the unsigned, like `unsigned char'.
Each kind of machine has a default for what `char' should be. It
is either like `unsigned char' by default or like `signed char'
by default. (Actually, at present, the default is always signed.)
The type `char' is always a distinct type from either `signed
char' or `unsigned char', even though its behavior is always just
like one of those two.
`-fsigned-char'
Let the type `char' be signed, like `signed char'.
`-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.
`-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.
`-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 are may be returned.
`-dLETTERS'
Says to make debugging dumps at times specified by LETTERS. Here are
the possible letters:
`r'
Dump after RTL generation.
`j'
Dump after first jump optimization.
`J'
Dump after last jump optimization.
`s'
Dump after CSE (including the jump optimization that sometimes
follows CSE).
`L'
Dump after loop optimization.
`f'
Dump after flow analysis.
`c'
Dump after instruction combination.
`l'
Dump after local register allocation.
`g'
Dump after global register allocation.
`m'
Print statistics on memory usage, at the end of the run.
`-pedantic'
Issue all the warnings demanded by strict ANSI standard C; reject all
programs that use forbidden extensions.
Valid ANSI standard C programs should compile properly with or without
this option (though a rare few will require `-ansi'). However,
without this option, certain GNU extensions and traditional C features
are supported as well. With this option, they are rejected. There is
no reason to use this option; it exists only to satisfy pedants.
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 C preprocessing. Some of these options make sense only
together with `-E' because they request preprocessor output that is not
suitable for actual compilation.
`-C'
Tell the preprocessor not to discard comments. Used with the `-E'
option.
`-IDIR'
Search directory DIR for include files.
`-I-'
Any directories specified 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 as the first search directory for `#include "FILE"'.
Therefore, the current directory is searched only if it is requested
explicitly with `-I.'. Specifying both `-I-' and `-I.' allows you to
control precisely which directories are searched before the current
one and which are searched after.
`-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.
Between `-nostdinc' and `-I-', you can eliminate all directories from
the search path except those you specify.
`-M'
Tell the preprocessor to output a rule suitable for `make' describing
the dependencies of each source 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 files
`#include'd in it. This rule may be a single line or may be continued
with `\'-newline if it is long.
`-M' implies `-E'.
`-MM'
Like `-M' but the output mentions only the user-header files included
with `#include "FILE"'. System header files included with `#include
<FILE>' are omitted.
`-MM' implies `-E'.
`-DMACRO'
Define macro MACRO with the empty string as its definition.
`-DMACRO=DEFN'
Define macro MACRO as DEFN.
`-UMACRO'
Undefine macro MACRO.
`-T'
Support ANSI C trigraphs. You don't want to know about this
brain-damage. The `-ansi' option also has this effect.
File: internals, Node: Installation, Next: Trouble, Prev: Options, Up: Top
Installing GNU CC
*****************
Here is the procedure for installing GNU CC on a Unix system.
* Menu:
* VMS Install:: See below for installation on VMS.
1. Edit `Makefile'. If you are using HPUX, you must make a few changes
described in comments at the beginning of the file.
2. Choose configuration files.
* Make a symbolic link named `config.h' to the top-level config
file for the machine you are using (*Note Config::.). This file
is responsible for defining information about the host machine.
It includes `tm.h'.
The file's name should be `config-MACHINE.h'. On VMS, use
`config-vms.h' rather than `config-vax.h'. On the HP 9000 series
300, use `config-hp9k3.h' rather than `config-m68k.h'.
If your system does not support symbolic links, you might want to
set up `config.h' to contain a `#include' command which refers to
the appropriate file.
* Make a symbolic link named `tm.h' to the machine-description
macro file for your machine (its name should be `tm-MACHINE.h').
For the 68000/68020, do not use `tm-m68k.h' directly; instead use
one of the files `tm-sun3.h', `tm-sun2.h', `tm-isi68.h',
`tm-news800.h' or `tm-3b1.h'. Each of those files includes
`tm-m68k.h' but sets up a few things differently as appropriate
to the specific model of machine.
There are two files you can use for a 680x0 running HPUX:
`tm-hp9k320.h' and `tm-hp9k320g.h'. Use the former if you are
installing GNU CC alone. The latter is for another option where
GNU CC together with the GNU assembler, linker, debugger and
other utilities are used to replace all of HPUX that deals with
compilation. Not all of the pieces of GNU software needed for
this mode of operation are as yet in distribution; full
instructions will appear here in the future.
For the 32000, use `tm-sequent.h' if you are using a Sequent
machine, or `tm-encore.h' for an Encore machine; otherwise,
perhaps `tm-ns32k.h' will work for you.
For the vax, use `tm-vax.h' on Unix, or `tm-vms.h' on VMS.
* Make a symbolic link named `md' to the machine description
pattern file (its name should be `MACHINE.md').
* Make a symbolic link named `aux-output.c' to the output
subroutine file for your machine (its name should be
`OUTPUT-MACHINE.c').
3. Make sure the Bison parser generator is installed. (This is unnecessary
if the Bison output file `parse.tab.c' is more recent than `parse.y'
and you do not plan to change `parse.y'.)
Note that if you have an old version of Bison you may get an error
from the line with the `%expect' directive. If so, simply remove that
line from `parse.y' and proceed.
4. If you are using a Sun, make sure the environment variable
`FLOAT_OPTION' is not set. If this option were set to `f68881' when
`gnulib' is compiled, the resulting code would demand to be linked
with a special startup file and will not link properly without special
pains.
5. Build the compiler. Just type `make' in the compiler directory.
6. Move the first-stage object files and executables into a subdirectory
with this command:
make stage1
The files are moved into a subdirectory named `stage1'. Once
installation is complete, you may wish to delete these files with `rm
-r stage1'.
7. Recompile the compiler with itself, with this command:
make CC=stage1/gcc CFLAGS="-g -O -Bstage1/"
On a 68000 or 68020 system lacking floating point hardware, unless you
have selected a `tm.h' file that expects by default that there is no
such hardware, do this instead:
make CC=stage1/gcc CFLAGS="-g -O -Bstage1/ -msoft-float"
8. If you wish to test the compiler by compiling it with itself one more
time, do this:
make stage2
make CC=stage2/gcc CFLAGS="-g -O -Bstage2/"
foreach file (*.o)
cmp $file stage2/$file
end
This will notify you if any of these stage 3 object files differs from
those of stage 2. Any difference, no matter how innocuous, indicates
that the stage 2 compiler has compiled GNU CC incorrectly, and is
therefore a potentially serious bug which you should investigate and
report (*Note Bugs::.).
9. Install the compiler driver, the compiler's passes and run-time support.
You can use the following command:
make install
This copies the files `cc1', `cpp' and `gnulib' to files `gcc-cc1',
`gcc-cpp' and `gcc-gnulib' in directory `/usr/local/lib', which is
where the compiler driver program looks for them. It also copies the
driver program `gcc' into the directory `/usr/local', so that it
appears in typical execution search paths.
*Warning: the GNU CPP may not work for `ioctl.h', `ttychars.h' and
other system header files unless the `-traditional' option is used.*
The bug is in the header files: at least on some machines, they rely
on behavior that is incompatible with ANSI C. This behavior consists
of substituting for macro argument names when they appear inside of
character constants. The `-traditional' option tells GNU CC to behave
the way these headers expect.
Because of this problem, you might prefer to configure GNU CC to use
the system's own C preprocessor. To do so, make the file
`/usr/local/lib/gcc-cpp' a link to `/lib/cpp'.
Alternatively, on Sun systems and 4.3BSD at least, you can correct the
include files by running the shell script `fixincludes'. This
installs modified, corrected copies of the files `ioctl.h' and
`ttychars.h' in a special directory where only GNU CC will normally
look for them.
The file `/usr/include/vaxuba/qvioctl.h' used in the X window system
needs a similar correction.
If you cannot install the compiler's passes and run-time support in
`/usr/local/lib', you can alternatively use the `-B' option to specify a
prefix by which they may be found. The compiler concatenates the prefix
with the names `cpp', `cc1' and `gnulib'. Thus, you can put the files in
a directory `/usr/foo/gcc' and specify `-B/usr/foo/gcc/' when you run GNU CC.
File: internals, Node: VMS Install, Prev: Installation, Up: Installation
Installing GNU CC on VMS
========================
The VMS version of GNU CC is distributed in an unusual tape format which
consists of several tape files. The first is a command file; the second is
an executable program which reads Unix tar format; the third is another
command file which uses this program to read the remainder of the tape.
To load the tape, it suffices to mount it `/foreign' and then do `@mta0:'
to execute the command file at the beginning of the tape.
The tape contains executables and object files as well as sources, so no
compilation is necessary unless you change the sources. (This is a good
thing, since you probably don't have any other C compiler.) If you must
recompile, here is how:
1. Copy the file `tm-vms.h' to `tm.h', `config-vms.h' to `config.h',
`vax.md' to `md.' and `output-vax.c' to `aux-output.c'.
2. Type `@make' to do recompile everything.
To install the `GCC' command so you can use the compiler easily, in the
same manner as you use the VMS C compiler, you must install the VMS CLD
file for GNU CC as follows:
1. Define the VMS logical names `GNU_CC' and `GNU_CC_INCLUDE' to point to
the directories where the GNU CC executables (`gcc-cpp', `gcc-cc1',
etc.) and the C include files are kept. This should be done with the
commands:
$ assign /super /system disk:[gcc] gnu_cc
$ assign /super /system disk:[gcc.include] gnu_cc_include
with the appropriate disk and directory names. These commands can be
placed in your system startup file so they will be executed whenever
the machine is rebooted.
2. Install the `GCC' command with the command line:
$ set command /table=sys$library:dcltables gnu_cc:gcc
Now you can invoke the compiler with a command like `gcc /verbose
file.c', which is equivalent to the command `gcc -v -c file.c' in Unix.
File: internals, Node: Trouble, Next: Incompatibilities, Prev: Installation, Up: Top
Trouble in Installation
***********************
Here are some of the things that have caused trouble for people installing
GNU CC.
On certain systems, defining certain environment variables such as
`CC' can interfere with the functioning of `make'.
File: internals, Node: Incompatibilities, Next: Extensions, Prev: Trouble, Up: Top
Incompatibilities of GNU CC
***************************
There are several noteworthy incompatibilities between GNU C and most
existing (non-ANSI) versions of C.
Ultimately our intention is that the `-traditional' option will eliminate
most of these incompatibilities by telling GNU C to behave like the other C
compilers.
* GNU CC normally makes string constants read-only. If several
identical-looking string constants are used, GNU CC stores only one
copy of the string.
One consequence is that you cannot call `mktemp' with a string
constant argument. The function `mktemp' always alters the string its
argument points to.
Another consequence is that `sscanf' does not work on some systems
when passed a string constant as its format control string. This is
because `sscanf' incorrectly tries to write into the string constant.
The best solution to these problems is to change the program to use
`char'-array variables with initialization strings for these purposes
instead of string constants. But if this is not possible, you can use
the `-fwritable-strings' flag, which directs GNU CC to handle string
constants the same way most C compilers do.
* GNU CC does not substitute macro arguments when they appear inside of
string constants. For example, the following macro in GNU CC
#define foo(a) "a"
will produce output `"a"' regardless of what the argument A is.
The `-traditional' option directs GNU CC to handle such cases (among
others) in the old-fashioned (non-ANSI) fashion.
* When you use `setjmp' and `longjmp', the only automatic variables
guaranteed to remain valid are those declared `volatile'. This is a
consequence of automatic register allocation. Consider this function:
jmp_buf j;
foo ()
{
int a, b;
a = fun1 ();
if (setjmp (j))
return a;
a = fun2 ();
/* `longjmp (j)' may be occur in `fun3'. */
return a + fun3 ();
}
Here `a' may or may not be restored to its first value when the
`longjmp' occurs. If `a' is allocated in a register, then its first
value is restored; otherwise, it keeps the last value stored in it.
If you use the `-W' option with the `-O' option, you will get a
warning when GNU CC thinks such a problem might be possible.
* Declarations of external variables and functions within a block apply
only to the block containing the declaration. In other words, they
have the same scope as any other declaration in the same place.
In some other C compilers, a `extern' declaration affects all the rest
of the file even if it happens within a block.
The `-traditional' option directs GNU C to treat all `extern'
declarations as global, like traditional compilers.
* In traditional C, you can combine `long', etc., with a typedef name,
as shown here:
typedef int foo;
typedef long foo bar;
In ANSI C, this is not allowed: `long' and other type modifiers
require an explicit `int'. Because this criterion is expressed by
Bison grammar rules rather than C code, the `-traditional' flag cannot
alter it.
* When compiling functions that return structures or unions, GNU CC
output code uses a method different from that used on most versions of
Unix. As a result, code compiled with GNU CC cannot call a
structure-returning function compiled with PCC, and vice versa.
The method used by GCC is as follows: a structure or union which is 1,
2, 4 or 8 bytes long is returned like a scalar. A structure or union
with any other size is stored into an address supplied by the caller
in a special, fixed register.
PCC usually handles all sizes of structures and unions by returning
the address of a block of static storage containing the value. This
method is not used in GCC because it is slower and nonreentrant.
On systems where PCC works this way, you may be able to make
GCC-compiled code call such functions that were compiled with PCC by
declaring them to return a pointer to the structure or union instead
of the structure or union itself. For example, instead of this:
struct foo nextfoo ();
write this:
struct foo *nextfoo ();
#define nextfoo *nextfoo
(Note that this assumes you are using the GNU preprocessor, so that
the ANSI antirecursion rules for macro expansions are effective.)