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gcc-1.23
Info file internals, produced by Makeinfo, -*- Text -*- from input
file internals.texinfo.
This file documents the internals of the GNU compiler.
Copyright (C) 1988 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 section entitled ``GNU CC General Public License'' is
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 section entitled ``GNU CC General Public
License'' and this permission notice may be included in translations
approved by the Free Software Foundation instead of in the original
English.
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 most of the description of the
National Semiconductor 32000 series cpu. He also wrote the code
for inline function integration and for the SPARC cpu and
Motorola 88000 cpu and part of the Sun FPA support.
* Jan Stein of the Chalmers Computer Society provided support for
Genix, as well as part of the 32000 machine description.
* Randy Smith finished the Sun FPA support.
* Robert Brown implemented the support for Encore 32000 systems.
* David Kashtan of SRI adapted GNU CC to the Vomit-Making System.
* Alex Crain provided changes for the 3b1.
* Greg Satz and Chris Hanson assisted in making GNU CC work on
HP-UX for the 9000 series 300.
* William Schelter did most of the work on the Intel 80386 support.
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'.
* Out-of-range floating point literals are not an error.
* In the preprocessor, comments convert to nothing at all,
rather than to a space. This allows traditional token
concatenation.
* In the preprocessor, macro arguments are recognized within
string constants in a macro definition (and their values
are stringified, though without additional quote marks,
when they appear in such a context). The preprocessor
always considers a string constant to end at a newline.
`-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 the operating system's native
format (for DBX or SDB).
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 `save_y' 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.
`-Wwrite-strings'
Give string constants the type `const char[LENGTH]' so that
copying the address of one into a non-`const' `char *' pointer
will get a warning. These warnings will help you find at
compile time code that can try to write into a string constant,
but only if you have been very careful about using `const' in
declarations and prototypes. Otherwise, it will just be a
nuisance; this is why we did not make `-Wall' request these
warnings.
`-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 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' searches
several directories.
`-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'
`-mc68020'
Generate output for a 68020 (rather than a 68000). This is
the default if you use the unmodified sources.
`-m68000'
`-mc68000'
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.
`-mfpa'
Generate output containing Sun FPA instructions for
floating point.
`-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, or any form of system
V, you must make a few changes described in comments at the
beginning of the file.
2. On a Sequent system, go to the Berkeley universe.
3. 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', with these
exceptions:
`config-vms.h'
for vaxen running VMS.
`config-vaxv.h'
for vaxen running system V.
`config-i386v.h'
for Intel 80386's running system V.
`config-sun4.h'
for Suns (model 3 or 4) running *operating system*
version 4.
`config-hp9k3.h'
for the HP 9000 series 300.
`config-gnx.h'
for the ns32000 running Genix
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').
If your system is a 68000, don't use the file `tm-m68k.h'
directly. Instead, use one of these files:
`tm-sun3.h'
for Sun 3 machines.
`tm-sun2.h'
for Sun 2 machines.
`tm-3b1.h'
for AT&T 3b1 (aka 7300 Unix PC).
`tm-isi68.h'
for Integrated Solutions systems.
`tm-news800.h'
for SONY News systems.
`tm-hp9k320.h'
for HPUX systems, if you are using GNU CC with the
system's assembler and linker.
`tm-hp9k320g.h'
for HPUX systems, if you are using the GNU assembler,
linker and other utilities. 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 vax, use `tm-vax.h' on BSD Unix, `tm-vaxv.h' on
system V, or `tm-vms.h' on VMS.
For the SPARC (Sun 4), use `tm-sparc.h'.
For the Motorola 88000, use `tm-m88k.h'. The support for
the 88000 has a few unfinished spots because there was no
way to run the output. Bugs are suspected in handling of
branch-tables and in the function prologue and epilogue.
For the 80386, don't use `tm-i386.h' directly. Use
`tm-i386v.h' if the target machine is running system V,
`tm-seq386.h' for a Sequent 386 system, or `tm-compaq.h'
for a Compaq.
For the 32000, use `tm-sequent.h' if you are using a
Sequent machine, or `tm-encore.h' for an Encore machine, or
`tm-gnx.h' if you are using Genix version 3; otherwise,
perhaps `tm-ns32k.h' will work for you.
Note that Genix has bugs in `alloca' and `malloc'; you must
get the compiled versions of these from GNU Emacs and edit
GNU CC's `Makefile' to use them.
Note that Encore systems are supported only under BSD.
* 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').
4. Make sure the Bison parser generator is installed. (This is
unnecessary if the Bison output files `c-parse.tab.c' and
`cexp.c' are more recent than `c-parse.y' and `cexp.y' and you
do not plan to change the `.y' files.)
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 `c-parse.y' and proceed.
5. 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.
6. Build the compiler. Just type `make' in the compiler directory.
7. 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'.
8. 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"
9. 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::.).
Aside from the `-B' option, the options should be the same as
when you made stage 2.
10. 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: there is a bug in `alloca' in the Sun library. To
avoid this bug, install the binaries of GNU CC that were
compiled by GNU CC. They use `alloca' as a built-in function
and never the one in the library.*
*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', `ttychars.h' and many others, in a special
directory where only GNU CC will normally look for them.
See the file `fixincludes' for a list of all the files we know
to require 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.
Also, you can specify an alternative default directory for these
files by setting the Make variable `libdir' when you make 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'.
* Cross compilation can run into trouble for certain machines
because some target machines' assemblers require floating point
numbers to be written as *integer* constants in certain contexts.
The compiler writes these integer constants by examining the
floating point value as an integer and printing that integer,
because this is simple to write and independent of the details
of the floating point representation. But this does not work if
the compiler is running on a different machine with an
incompatible floating point format, or even a different
byte-ordering.
It is possible to fix this by writing machine-independent code
which understands the floating point representation of the
target machine. I am not interested in doing that much work to
compensate for bugs in assemblers.
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