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This is Info file gcc.info, produced by Makeinfo-1.55 from the input
file gcc.texi.
This file documents the use and the internals of the GNU compiler.
Published by the Free Software Foundation 675 Massachusetts Avenue
Cambridge, MA 02139 USA
Copyright (C) 1988, 1989, 1992, 1993, 1994 Free Software Foundation,
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License," "Funding for
Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License," "Funding for Free Software," and "Protect Your Freedom--Fight
`Look And Feel'", and this permission notice, may be included in
translations approved by the Free Software Foundation instead of in the
original English.
File: gcc.info, Node: Min and Max, Next: Destructors and Goto, Prev: Naming Results, Up: C++ Extensions
Minimum and Maximum Operators in C++
====================================
It is very convenient to have operators which return the "minimum"
or the "maximum" of two arguments. In GNU C++ (but not in GNU C),
`A <? B'
is the "minimum", returning the smaller of the numeric values A
and B;
`A >? B'
is the "maximum", returning the larger of the numeric values A and
B.
These operations are not primitive in ordinary C++, since you can
use a macro to return the minimum of two things in C++, as in the
following example.
#define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))
You might then use `int min = MIN (i, j);' to set MIN to the minimum
value of variables I and J.
However, side effects in `X' or `Y' may cause unintended behavior.
For example, `MIN (i++, j++)' will fail, incrementing the smaller
counter twice. A GNU C extension allows you to write safe macros that
avoid this kind of problem (*note Naming an Expression's Type: Naming
Types.). However, writing `MIN' and `MAX' as macros also forces you to
use function-call notation notation for a fundamental arithmetic
operation. Using GNU C++ extensions, you can write `int min = i <? j;'
instead.
Since `<?' and `>?' are built into the compiler, they properly
handle expressions with side-effects; `int min = i++ <? j++;' works
correctly.
File: gcc.info, Node: Destructors and Goto, Next: C++ Interface, Prev: Min and Max, Up: C++ Extensions
`goto' and Destructors in GNU C++
=================================
In C++ programs, you can safely use the `goto' statement. When you
use it to exit a block which contains aggregates requiring destructors,
the destructors will run before the `goto' transfers control. (In ANSI
C++, `goto' is restricted to targets within the current block.)
The compiler still forbids using `goto' to *enter* a scope that
requires constructors.
File: gcc.info, Node: C++ Interface, Next: Template Instantiation, Prev: Destructors and Goto, Up: C++ Extensions
Declarations and Definitions in One Header
==========================================
C++ object definitions can be quite complex. In principle, your
source code will need two kinds of things for each object that you use
across more than one source file. First, you need an "interface"
specification, describing its structure with type declarations and
function prototypes. Second, you need the "implementation" itself. It
can be tedious to maintain a separate interface description in a header
file, in parallel to the actual implementation. It is also dangerous,
since separate interface and implementation definitions may not remain
parallel.
With GNU C++, you can use a single header file for both purposes.
*Warning:* The mechanism to specify this is in transition. For the
nonce, you must use one of two `#pragma' commands; in a future
release of GNU C++, an alternative mechanism will make these
`#pragma' commands unnecessary.
The header file contains the full definitions, but is marked with
`#pragma interface' in the source code. This allows the compiler to
use the header file only as an interface specification when ordinary
source files incorporate it with `#include'. In the single source file
where the full implementation belongs, you can use either a naming
convention or `#pragma implementation' to indicate this alternate use
of the header file.
`#pragma interface'
`#pragma interface "SUBDIR/OBJECTS.h"'
Use this directive in *header files* that define object classes,
to save space in most of the object files that use those classes.
Normally, local copies of certain information (backup copies of
inline member functions, debugging information, and the internal
tables that implement virtual functions) must be kept in each
object file that includes class definitions. You can use this
pragma to avoid such duplication. When a header file containing
`#pragma interface' is included in a compilation, this auxiliary
information will not be generated (unless the main input source
file itself uses `#pragma implementation'). Instead, the object
files will contain references to be resolved at link time.
The second form of this directive is useful for the case where you
have multiple headers with the same name in different directories.
If you use this form, you must specify the same string to `#pragma
implementation'.
`#pragma implementation'
`#pragma implementation "OBJECTS.h"'
Use this pragma in a *main input file*, when you want full output
from included header files to be generated (and made globally
visible). The included header file, in turn, should use `#pragma
interface'. Backup copies of inline member functions, debugging
information, and the internal tables used to implement virtual
functions are all generated in implementation files.
If you use `#pragma implementation' with no argument, it applies to
an include file with the same basename(1) as your source file.
For example, in `allclass.cc', `#pragma implementation' by itself
is equivalent to `#pragma implementation "allclass.h"'.
In versions of GNU C++ prior to 2.6.0 `allclass.h' was treated as
an implementation file whenever you would include it from
`allclass.cc' even if you never specified `#pragma
implementation'. This was deemed to be more trouble than it was
worth, however, and disabled.
If you use an explicit `#pragma implementation', it must appear in
your source file *before* you include the affected header files.
Use the string argument if you want a single implementation file to
include code from multiple header files. (You must also use
`#include' to include the header file; `#pragma implementation'
only specifies how to use the file--it doesn't actually include
it.)
There is no way to split up the contents of a single header file
into multiple implementation files.
`#pragma implementation' and `#pragma interface' also have an effect
on function inlining.
If you define a class in a header file marked with `#pragma
interface', the effect on a function defined in that class is similar to
an explicit `extern' declaration--the compiler emits no code at all to
define an independent version of the function. Its definition is used
only for inlining with its callers.
Conversely, when you include the same header file in a main source
file that declares it as `#pragma implementation', the compiler emits
code for the function itself; this defines a version of the function
that can be found via pointers (or by callers compiled without
inlining). If all calls to the function can be inlined, you can avoid
emitting the function by compiling with `-fno-implement-inlines'. If
any calls were not inlined, you will get linker errors.
---------- Footnotes ----------
(1) A file's "basename" was the name stripped of all leading path
information and of trailing suffixes, such as `.h' or `.C' or `.cc'.
File: gcc.info, Node: Template Instantiation, Next: C++ Signatures, Prev: C++ Interface, Up: C++ Extensions
Where's the Template?
=====================
C++ templates are the first language feature to require more
intelligence from the environment than one usually finds on a UNIX
system. Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise. There are two basic approaches to this
problem, which I will refer to as the Borland model and the Cfront
model.
Borland model
Borland C++ solved the template instantiation problem by adding
the code equivalent of common blocks to their linker; template
instances are emitted in each translation unit that uses them, and
they are collapsed together at run time. The advantage of this
model is that the linker only has to consider the object files
themselves; there is no external complexity to worry about. This
disadvantage is that compilation time is increased because the
template code is being compiled repeatedly. Code written for this
model tends to include definitions of all member templates in the
header file, since they must be seen to be compiled.
Cfront model
The AT&T C++ translator, Cfront, solved the template instantiation
problem by creating the notion of a template repository, an
automatically maintained place where template instances are
stored. As individual object files are built, notes are placed in
the repository to record where templates and potential type
arguments were seen so that the subsequent instantiation step
knows where to find them. At link time, any needed instances are
generated and linked in. The advantages of this model are more
optimal compilation speed and the ability to use the system
linker; to implement the Borland model a compiler vendor also
needs to replace the linker. The disadvantages are vastly
increased complexity, and thus potential for error; theoretically,
this should be just as transparent, but in practice it has been
very difficult to build multiple programs in one directory and one
program in multiple directories using Cfront. Code written for
this model tends to separate definitions of non-inline member
templates into a separate file, which is magically found by the
link preprocessor when a template needs to be instantiated.
Currently, g++ implements neither automatic model. The g++ team
hopes to have a repository working for 2.7.0. In the mean time, you
have three options for dealing with template instantiations:
1. Do nothing. Pretend g++ does implement automatic instantiation
management. Code written for the Borland model will work fine, but
each translation unit will contain instances of each of the
templates it uses. In a large program, this can lead to an
unacceptable amount of code duplication.
2. Add `#pragma interface' to all files containing template
definitions. For each of these files, add `#pragma implementation
"FILENAME"' to the top of some `.C' file which `#include's it.
Then compile everything with -fexternal-templates. The templates
will then only be expanded in the translation unit which
implements them (i.e. has a `#pragma implementation' line for the
file where they live); all other files will use external
references. If you're lucky, everything should work properly. If
you get undefined symbol errors, you need to make sure that each
template instance which is used in the program is used in the file
which implements that template. If you don't have any use for a
particular instance in that file, you can just instantiate it
explicitly, using the syntax from the latest C++ working paper:
template class A<int>;
template ostream& operator << (ostream&, const A<int>&);
This strategy will work with code written for either model. If
you are using code written for the Cfront model, the file
containing a class template and the file containing its member
templates should be implemented in the same translation unit.
A slight variation on this approach is to use the flag
-falt-external-templates instead; this flag causes template
instances to be emitted in the translation unit that implements
the header where they are first instantiated, rather than the one
which implements the file where the templates are defined. This
header must be the same in all translation units, or things are
likely to break.
*Note Declarations and Definitions in One Header: C++ Interface,
for more discussion of these pragmas.
3. Explicitly instantiate all the template instances you use, and
compile with -fno-implicit-templates. This is probably your best
bet; it may require more knowledge of exactly which templates you
are using, but it's less mysterious than the previous approach,
and it doesn't require any `#pragma's or other g++-specific code.
You can scatter the instantiations throughout your program, you
can create one big file to do all the instantiations, or you can
create tiny files like
#include "Foo.h"
#include "Foo.cc"
template class Foo<int>;
for each instance you need, and create a template instantiation
library from those. I'm partial to the last, but your mileage may
vary. If you are using Cfront-model code, you can probably get
away with not using -fno-implicit-templates when compiling files
that don't `#include' the member template definitions.
File: gcc.info, Node: C++ Signatures, Prev: Template Instantiation, Up: C++ Extensions
Type Abstraction using Signatures
=================================
In GNU C++, you can use the keyword `signature' to define a
completely abstract class interface as a datatype. You can connect this
abstraction with actual classes using signature pointers. If you want
to use signatures, run the GNU compiler with the `-fhandle-signatures'
command-line option. (With this option, the compiler reserves a second
keyword `sigof' as well, for a future extension.)
Roughly, signatures are type abstractions or interfaces of classes.
Some other languages have similar facilities. C++ signatures are
related to ML's signatures, Haskell's type classes, definition modules
in Modula-2, interface modules in Modula-3, abstract types in Emerald,
type modules in Trellis/Owl, categories in Scratchpad II, and types in
POOL-I. For a more detailed discussion of signatures, see `Signatures:
A C++ Extension for Type Abstraction and Subtype Polymorphism' by
Gerald Baumgartner and Vincent F. Russo (Tech report CSD-TR-93-059,
Dept. of Computer Sciences, Purdue University, September 1993, to
appear in *Software Practice & Experience*). You can get the tech
report by anonymous FTP from `ftp.cs.purdue.edu' in
`pub/reports/TR93-059.PS.Z'.
Syntactically, a signature declaration is a collection of member
function declarations and nested type declarations. For example, this
signature declaration defines a new abstract type `S' with member
functions `int foo ()' and `int bar (int)':
signature S
{
int foo ();
int bar (int);
};
Since signature types do not include implementation definitions, you
cannot write an instance of a signature directly. Instead, you can
define a pointer to any class that contains the required interfaces as a
"signature pointer". Such a class "implements" the signature type.
To use a class as an implementation of `S', you must ensure that the
class has public member functions `int foo ()' and `int bar (int)'.
The class can have other member functions as well, public or not; as
long as it offers what's declared in the signature, it is suitable as
an implementation of that signature type.
For example, suppose that `C' is a class that meets the requirements
of signature `S' (`C' "conforms to" `S'). Then
C obj;
S * p = &obj;
defines a signature pointer `p' and initializes it to point to an
object of type `C'. The member function call `int i = p->foo ();'
executes `obj.foo ()'.
Abstract virtual classes provide somewhat similar facilities in
standard C++. There are two main advantages to using signatures
instead:
1. Subtyping becomes independent from inheritance. A class or
signature type `T' is a subtype of a signature type `S'
independent of any inheritance hierarchy as long as all the member
functions declared in `S' are also found in `T'. So you can
define a subtype hierarchy that is completely independent from any
inheritance (implementation) hierarchy, instead of being forced to
use types that mirror the class inheritance hierarchy.
2. Signatures allow you to work with existing class hierarchies as
implementations of a signature type. If those class hierarchies
are only available in compiled form, you're out of luck with
abstract virtual classes, since an abstract virtual class cannot
be retrofitted on top of existing class hierarchies. So you would
be required to write interface classes as subtypes of the abstract
virtual class.
There is one more detail about signatures. A signature declaration
can contain member function *definitions* as well as member function
declarations. A signature member function with a full definition is
called a *default implementation*; classes need not contain that
particular interface in order to conform. For example, a class `C' can
conform to the signature
signature T
{
int f (int);
int f0 () { return f (0); };
};
whether or not `C' implements the member function `int f0 ()'. If you
define `C::f0', that definition takes precedence; otherwise, the
default implementation `S::f0' applies.
File: gcc.info, Node: Trouble, Next: Bugs, Prev: C++ Extensions, Up: Top
Known Causes of Trouble with GNU CC
***********************************
This section describes known problems that affect users of GNU CC.
Most of these are not GNU CC bugs per se--if they were, we would fix
them. But the result for a user may be like the result of a bug.
Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.
* Menu:
* Actual Bugs:: Bugs we will fix later.
* Installation Problems:: Problems that manifest when you install GNU CC.
* Cross-Compiler Problems:: Common problems of cross compiling with GNU CC.
* Interoperation:: Problems using GNU CC with other compilers,
and with certain linkers, assemblers and debuggers.
* External Bugs:: Problems compiling certain programs.
* Incompatibilities:: GNU CC is incompatible with traditional C.
* Fixed Headers:: GNU C uses corrected versions of system header files.
This is necessary, but doesn't always work smoothly.
* Disappointments:: Regrettable things we can't change, but not quite bugs.
* C++ Misunderstandings:: Common misunderstandings with GNU C++.
* Protoize Caveats:: Things to watch out for when using `protoize'.
* Non-bugs:: Things we think are right, but some others disagree.
* Warnings and Errors:: Which problems in your code get warnings,
and which get errors.
File: gcc.info, Node: Actual Bugs, Next: Installation Problems, Up: Trouble
Actual Bugs We Haven't Fixed Yet
================================
* The `fixincludes' script interacts badly with automounters; if the
directory of system header files is automounted, it tends to be
unmounted while `fixincludes' is running. This would seem to be a
bug in the automounter. We don't know any good way to work around
it.
* The `fixproto' script will sometimes add prototypes for the
`sigsetjmp' and `siglongjmp' functions that reference the
`jmp_buf' type before that type is defined. To work around this,
edit the offending file and place the typedef in front of the
prototypes.
* There are several obscure case of mis-using struct, union, and
enum tags that are not detected as errors by the compiler.
* When `-pedantic-errors' is specified, GNU C will incorrectly give
an error message when a function name is specified in an expression
involving the comma operator.
* Loop unrolling doesn't work properly for certain C++ programs.
This is a bug in the C++ front end. It sometimes emits incorrect
debug info, and the loop unrolling code is unable to recover from
this error.
File: gcc.info, Node: Installation Problems, Next: Cross-Compiler Problems, Prev: Actual Bugs, Up: Trouble
Installation Problems
=====================
This is a list of problems (and some apparent problems which don't
really mean anything is wrong) that show up during installation of GNU
* On certain systems, defining certain environment variables such as
`CC' can interfere with the functioning of `make'.
* If you encounter seemingly strange errors when trying to build the
compiler in a directory other than the source directory, it could
be because you have previously configured the compiler in the
source directory. Make sure you have done all the necessary
preparations. *Note Other Dir::.
* If you build GNU CC on a BSD system using a directory stored in a
System V file system, problems may occur in running `fixincludes'
if the System V file system doesn't support symbolic links. These
problems result in a failure to fix the declaration of `size_t' in
`sys/types.h'. If you find that `size_t' is a signed type and
that type mismatches occur, this could be the cause.
The solution is not to use such a directory for building GNU CC.
* In previous versions of GNU CC, the `gcc' driver program looked for
`as' and `ld' in various places; for example, in files beginning
with `/usr/local/lib/gcc-'. GNU CC version 2 looks for them in
the directory `/usr/local/lib/gcc-lib/TARGET/VERSION'.
Thus, to use a version of `as' or `ld' that is not the system
default, for example `gas' or GNU `ld', you must put them in that
directory (or make links to them from that directory).
* Some commands executed when making the compiler may fail (return a
non-zero status) and be ignored by `make'. These failures, which
are often due to files that were not found, are expected, and can
safely be ignored.
* It is normal to have warnings in compiling certain files about
unreachable code and about enumeration type clashes. These files'
names begin with `insn-'. Also, `real.c' may get some warnings
that you can ignore.
* Sometimes `make' recompiles parts of the compiler when installing
the compiler. In one case, this was traced down to a bug in
`make'. Either ignore the problem or switch to GNU Make.
* If you have installed a program known as purify, you may find that
it causes errors while linking `enquire', which is part of building
GNU CC. The fix is to get rid of the file `real-ld' which purify
installs--so that GNU CC won't try to use it.
* On Linux SLS 1.01, there is a problem with `libc.a': it does not
contain the obstack functions. However, GNU CC assumes that the
obstack functions are in `libc.a' when it is the GNU C library.
To work around this problem, change the `__GNU_LIBRARY__'
conditional around line 31 to `#if 1'.
* On some 386 systems, building the compiler never finishes because
`enquire' hangs due to a hardware problem in the motherboard--it
reports floating point exceptions to the kernel incorrectly. You
can install GNU CC except for `float.h' by patching out the
command to run `enquire'. You may also be able to fix the problem
for real by getting a replacement motherboard. This problem was
observed in Revision E of the Micronics motherboard, and is fixed
in Revision F. It has also been observed in the MYLEX MXA-33
motherboard.
If you encounter this problem, you may also want to consider
removing the FPU from the socket during the compilation.
Alternatively, if you are running SCO Unix, you can reboot and
force the FPU to be ignored. To do this, type `hd(40)unix auto
ignorefpu'.
* On some 386 systems, GNU CC crashes trying to compile `enquire.c'.
This happens on machines that don't have a 387 FPU chip. On 386
machines, the system kernel is supposed to emulate the 387 when you
don't have one. The crash is due to a bug in the emulator.
One of these systems is the Unix from Interactive Systems: 386/ix.
On this system, an alternate emulator is provided, and it does
work. To use it, execute this command as super-user:
ln /etc/emulator.rel1 /etc/emulator
and then reboot the system. (The default emulator file remains
present under the name `emulator.dflt'.)
Try using `/etc/emulator.att', if you have such a problem on the
SCO system.
Another system which has this problem is Esix. We don't know
whether it has an alternate emulator that works.
On NetBSD 0.8, a similar problem manifests itself as these error
messages:
enquire.c: In function `fprop':
enquire.c:2328: floating overflow
* On SCO systems, when compiling GNU CC with the system's compiler,
do not use `-O'. Some versions of the system's compiler miscompile
GNU CC with `-O'.
* Sometimes on a Sun 4 you may observe a crash in the program
`genflags' or `genoutput' while building GNU CC. This is said to
be due to a bug in `sh'. You can probably get around it by running
`genflags' or `genoutput' manually and then retrying the `make'.
* On Solaris 2, executables of GNU CC version 2.0.2 are commonly
available, but they have a bug that shows up when compiling current
versions of GNU CC: undefined symbol errors occur during assembly
if you use `-g'.
The solution is to compile the current version of GNU CC without
`-g'. That makes a working compiler which you can use to recompile
with `-g'.
* Solaris 2 comes with a number of optional OS packages. Some of
these packages are needed to use GNU CC fully. If you did not
install all optional packages when installing Solaris, you will
need to verify that the packages that GNU CC needs are installed.
To check whether an optional package is installed, use the
`pkginfo' command. To add an optional package, use the `pkgadd'
command. For further details, see the Solaris documentation.
For Solaris 2.0 and 2.1, GNU CC needs six packages: `SUNWarc',
`SUNWbtool', `SUNWesu', `SUNWhea', `SUNWlibm', and `SUNWtoo'.
For Solaris 2.2, GNU CC needs an additional seventh package:
`SUNWsprot'.
* On Solaris 2, trying to use the linker and other tools in
`/usr/ucb' to install GNU CC has been observed to cause trouble.
For example, the linker may hang indefinitely. The fix is to
remove `/usr/ucb' from your `PATH'.
* If you use the 1.31 version of the MIPS assembler (such as was
shipped with Ultrix 3.1), you will need to use the
-fno-delayed-branch switch when optimizing floating point code.
Otherwise, the assembler will complain when the GCC compiler fills
a branch delay slot with a floating point instruction, such as
`add.d'.
* If on a MIPS system you get an error message saying "does not have
gp sections for all it's [sic] sectons [sic]", don't worry about
it. This happens whenever you use GAS with the MIPS linker, but
there is not really anything wrong, and it is okay to use the
output file. You can stop such warnings by installing the GNU
linker.
It would be nice to extend GAS to produce the gp tables, but they
are optional, and there should not be a warning about their
absence.
* In Ultrix 4.0 on the MIPS machine, `stdio.h' does not work with GNU
CC at all unless it has been fixed with `fixincludes'. This causes
problems in building GNU CC. Once GNU CC is installed, the
problems go away.
To work around this problem, when making the stage 1 compiler,
specify this option to Make:
GCC_FOR_TARGET="./xgcc -B./ -I./include"
When making stage 2 and stage 3, specify this option:
CFLAGS="-g -I./include"
* Users have reported some problems with version 2.0 of the MIPS
compiler tools that were shipped with Ultrix 4.1. Version 2.10
which came with Ultrix 4.2 seems to work fine.
Users have also reported some problems with version 2.20 of the
MIPS compiler tools that were shipped with RISC/os 4.x. The
earlier version 2.11 seems to work fine.
* Some versions of the MIPS linker will issue an assertion failure
when linking code that uses `alloca' against shared libraries on
RISC-OS 5.0, and DEC's OSF/1 systems. This is a bug in the
linker, that is supposed to be fixed in future revisions. To
protect against this, GNU CC passes `-non_shared' to the linker
unless you pass an explicit `-shared' or `-call_shared' switch.
* On System V release 3, you may get this error message while
linking:
ld fatal: failed to write symbol name SOMETHING
in strings table for file WHATEVER
This probably indicates that the disk is full or your ULIMIT won't
allow the file to be as large as it needs to be.
This problem can also result because the kernel parameter `MAXUMEM'
is too small. If so, you must regenerate the kernel and make the
value much larger. The default value is reported to be 1024; a
value of 32768 is said to work. Smaller values may also work.
* On System V, if you get an error like this,
/usr/local/lib/bison.simple: In function `yyparse':
/usr/local/lib/bison.simple:625: virtual memory exhausted
that too indicates a problem with disk space, ULIMIT, or `MAXUMEM'.
* Current GNU CC versions probably do not work on version 2 of the
NeXT operating system.
* On NeXTStep 3.0, the Objective C compiler does not work, due,
apparently, to a kernel bug that it happens to trigger. This
problem does not happen on 3.1.
* On the Tower models 4N0 and 6N0, by default a process is not
allowed to have more than one megabyte of memory. GNU CC cannot
compile itself (or many other programs) with `-O' in that much
memory.
To solve this problem, reconfigure the kernel adding the following
line to the configuration file:
MAXUMEM = 4096
* On HP 9000 series 300 or 400 running HP-UX release 8.0, there is a
bug in the assembler that must be fixed before GNU CC can be
built. This bug manifests itself during the first stage of
compilation, while building `libgcc2.a':
_floatdisf
cc1: warning: `-g' option not supported on this version of GCC
cc1: warning: `-g1' option not supported on this version of GCC
./xgcc: Internal compiler error: program as got fatal signal 11
A patched version of the assembler is available by anonymous ftp
from `altdorf.ai.mit.edu' as the file
`archive/cph/hpux-8.0-assembler'. If you have HP software support,
the patch can also be obtained directly from HP, as described in
the following note:
This is the patched assembler, to patch SR#1653-010439, where
the assembler aborts on floating point constants.
The bug is not really in the assembler, but in the shared
library version of the function "cvtnum(3c)". The bug on
"cvtnum(3c)" is SR#4701-078451. Anyway, the attached
assembler uses the archive library version of "cvtnum(3c)"
and thus does not exhibit the bug.
This patch is also known as PHCO_4484.
* On HP-UX version 8.05, but not on 8.07 or more recent versions,
the `fixproto' shell script triggers a bug in the system shell.
If you encounter this problem, upgrade your operating system or
use BASH (the GNU shell) to run `fixproto'.
* Some versions of the Pyramid C compiler are reported to be unable
to compile GNU CC. You must use an older version of GNU CC for
bootstrapping. One indication of this problem is if you get a
crash when GNU CC compiles the function `muldi3' in file
`libgcc2.c'.
You may be able to succeed by getting GNU CC version 1, installing
it, and using it to compile GNU CC version 2. The bug in the
Pyramid C compiler does not seem to affect GNU CC version 1.
* There may be similar problems on System V Release 3.1 on 386
systems.
* On the Intel Paragon (an i860 machine), if you are using operating
system version 1.0, you will get warnings or errors about
redefinition of `va_arg' when you build GNU CC.
If this happens, then you need to link most programs with the
library `iclib.a'. You must also modify `stdio.h' as follows:
before the lines
#if defined(__i860__) && !defined(_VA_LIST)
#include <va_list.h>
insert the line
#if __PGC__
and after the lines
extern int vprintf(const char *, va_list );
extern int vsprintf(char *, const char *, va_list );
#endif
insert the line
#endif /* __PGC__ */
These problems don't exist in operating system version 1.1.
* On the Altos 3068, programs compiled with GNU CC won't work unless
you fix a kernel bug. This happens using system versions V.2.2
1.0gT1 and V.2.2 1.0e and perhaps later versions as well. See the
file `README.ALTOS'.
* You will get several sorts of compilation and linking errors on the
we32k if you don't follow the special instructions. *Note
Configurations::.
* A bug in the HP-UX 8.05 (and earlier) shell will cause the fixproto
program to report an error of the form:
./fixproto: sh internal 1K buffer overflow
To fix this, change the first line of the fixproto script to look
like:
#!/bin/ksh
File: gcc.info, Node: Cross-Compiler Problems, Next: Interoperation, Prev: Installation Problems, Up: Trouble
Cross-Compiler Problems
=======================
You may run into problems with cross compilation on certain machines,
for several reasons.
* 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.
In addition, correct constant folding of floating point values
requires representing them in the target machine's format. (The C
standard does not quite require this, but in practice it is the
only way to win.)
It is now possible to overcome these problems by defining macros
such as `REAL_VALUE_TYPE'. But doing so is a substantial amount of
work for each target machine. *Note Cross-compilation::.
* At present, the program `mips-tfile' which adds debug support to
object files on MIPS systems does not work in a cross compile
environment.
File: gcc.info, Node: Interoperation, Next: External Bugs, Prev: Cross-Compiler Problems, Up: Trouble
Interoperation
==============
This section lists various difficulties encountered in using GNU C or
GNU C++ together with other compilers or with the assemblers, linkers,
libraries and debuggers on certain systems.
* Objective C does not work on the RS/6000.
* GNU C++ does not do name mangling in the same way as other C++
compilers. This means that object files compiled with one compiler
cannot be used with another.
This effect is intentional, to protect you from more subtle
problems. Compilers differ as to many internal details of C++
implementation, including: how class instances are laid out, how
multiple inheritance is implemented, and how virtual function
calls are handled. If the name encoding were made the same, your
programs would link against libraries provided from other
compilers--but the programs would then crash when run.
Incompatible libraries are then detected at link time, rather than
at run time.
* Older GDB versions sometimes fail to read the output of GNU CC
version 2. If you have trouble, get GDB version 4.4 or later.
* DBX rejects some files produced by GNU CC, though it accepts
similar constructs in output from PCC. Until someone can supply a
coherent description of what is valid DBX input and what is not,
there is nothing I can do about these problems. You are on your
own.
* The GNU assembler (GAS) does not support PIC. To generate PIC
code, you must use some other assembler, such as `/bin/as'.
* On some BSD systems, including some versions of Ultrix, use of
profiling causes static variable destructors (currently used only
in C++) not to be run.
* Use of `-I/usr/include' may cause trouble.
Many systems come with header files that won't work with GNU CC
unless corrected by `fixincludes'. The corrected header files go
in a new directory; GNU CC searches this directory before
`/usr/include'. If you use `-I/usr/include', this tells GNU CC to
search `/usr/include' earlier on, before the corrected headers.
The result is that you get the uncorrected header files.
Instead, you should use these options (when compiling C programs):
-I/usr/local/lib/gcc-lib/TARGET/VERSION/include -I/usr/include
For C++ programs, GNU CC also uses a special directory that
defines C++ interfaces to standard C subroutines. This directory
is meant to be searched *before* other standard include
directories, so that it takes precedence. If you are compiling
C++ programs and specifying include directories explicitly, use
this option first, then the two options above:
-I/usr/local/lib/g++-include
* On some SGI systems, when you use `-lgl_s' as an option, it gets
translated magically to `-lgl_s -lX11_s -lc_s'. Naturally, this
does not happen when you use GNU CC. You must specify all three
options explicitly.
* On a Sparc, GNU CC aligns all values of type `double' on an 8-byte
boundary, and it expects every `double' to be so aligned. The Sun
compiler usually gives `double' values 8-byte alignment, with one
exception: function arguments of type `double' may not be aligned.
As a result, if a function compiled with Sun CC takes the address
of an argument of type `double' and passes this pointer of type
`double *' to a function compiled with GNU CC, dereferencing the
pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program
with GNU CC. Another solution is to modify the function that is
compiled with Sun CC to copy the argument into a local variable;
local variables are always properly aligned. A third solution is
to modify the function that uses the pointer to dereference it via
the following function `access_double' instead of directly with
`*':
inline double
access_double (double *unaligned_ptr)
{
union d2i { double d; int i[2]; };
union d2i *p = (union d2i *) unaligned_ptr;
union d2i u;
u.i[0] = p->i[0];
u.i[1] = p->i[1];
return u.d;
}
Storing into the pointer can be done likewise with the same union.
* On Solaris, the `malloc' function in the `libmalloc.a' library may
allocate memory that is only 4 byte aligned. Since GNU CC on the
Sparc assumes that doubles are 8 byte aligned, this may result in a
fatal signal if doubles are stored in memory allocated by the
`libmalloc.a' library.
The solution is to not use the `libmalloc.a' library. Use instead
`malloc' and related functions from `libc.a'; they do not have
this problem.
* Sun forgot to include a static version of `libdl.a' with some
versions of SunOS (mainly 4.1). This results in undefined symbols
when linking static binaries (that is, if you use `-static'). If
you see undefined symbols `_dlclose', `_dlsym' or `_dlopen' when
linking, compile and link against the file `mit/util/misc/dlsym.c'
from the MIT version of X windows.
* The 128-bit long double format that the Sparc port supports
currently works by using the architecturally defined quad-word
floating point instructions. Since there is no hardware that
supports these instructions they must be emulated by the operating
system. Long doubles do not work in Sun OS versions 4.0.3 and
earlier, because the kernel eumulator uses an obsolete and
incompatible format. Long doubles do not work in Sun OS versions
4.1.1 to 4.1.3 because of emululator bugs that cause random
unpredicatable failures. Long doubles appear to work in Sun OS 5.x
(Solaris 2.x).
* On HP-UX version 9.01 on the HP PA, the HP compiler `cc' does not
compile GNU CC correctly. We do not yet know why. However, GNU CC
compiled on earlier HP-UX versions works properly on HP-UX 9.01
and can compile itself properly on 9.01.
* On the HP PA machine, ADB sometimes fails to work on functions
compiled with GNU CC. Specifically, it fails to work on functions
that use `alloca' or variable-size arrays. This is because GNU CC
doesn't generate HP-UX unwind descriptors for such functions. It
may even be impossible to generate them.
* Debugging (`-g') is not supported on the HP PA machine, unless you
use the preliminary GNU tools (*note Installation::.).
* Taking the address of a label may generate errors from the HP-UX
PA assembler. GAS for the PA does not have this problem.
* Using floating point parameters for indirect calls to static
functions will not work when using the HP assembler. There simply
is no way for GCC to specify what registers hold arguments for
static functions when using the HP assembler. GAS for the PA does
not have this problem.
* For some very large functions you may receive errors from the HP
linker complaining about an out of bounds unconditional branch
offset. Fixing this problem correctly requires fixing problems in
GNU CC and GAS. We hope to fix this in time for GNU CC 2.6.
Until then you can work around by making your function smaller,
and if you are using GAS, splitting the function into multiple
source files may be necessary.
* GNU CC compiled code sometimes emits warnings from the HP-UX
assembler of the form:
(warning) Use of GR3 when
frame >= 8192 may cause conflict.
These warnings are harmless and can be safely ignored.
* The current version of the assembler (`/bin/as') for the RS/6000
has certain problems that prevent the `-g' option in GCC from
working. Note that `Makefile.in' uses `-g' by default when
compiling `libgcc2.c'.
IBM has produced a fixed version of the assembler. The upgraded
assembler unfortunately was not included in any of the AIX 3.2
update PTF releases (3.2.2, 3.2.3, or 3.2.3e). Users of AIX 3.1
should request PTF U403044 from IBM and users of AIX 3.2 should
request PTF U416277. See the file `README.RS6000' for more
details on these updates.
You can test for the presense of a fixed assembler by using the
command
as -u < /dev/null
If the command exits normally, the assembler fix already is
installed. If the assembler complains that "-u" is an unknown
flag, you need to order the fix.
* On the IBM RS/6000, compiling code of the form
extern int foo;
... foo ...
static int foo;
will cause the linker to report an undefined symbol `foo'.
Although this behavior differs from most other systems, it is not a
bug because redefining an `extern' variable as `static' is
undefined in ANSI C.
* AIX on the RS/6000 provides support (NLS) for environments outside
of the United States. Compilers and assemblers use NLS to support
locale-specific representations of various objects including
floating-point numbers ("." vs "," for separating decimal
fractions). There have been problems reported where the library
linked with GCC does not produce the same floating-point formats
that the assembler accepts. If you have this problem, set the
LANG environment variable to "C" or "En_US".
* Even if you specify `-fdollars-in-identifiers', you cannot
successfully use `$' in identifiers on the RS/6000 due to a
restriction in the IBM assembler. GAS supports these identifiers.
* On the RS/6000, XLC version 1.3.0.0 will miscompile `jump.c'. XLC
version 1.3.0.1 or later fixes this problem. You can obtain
XLC-1.3.0.2 by requesting PTF 421749 from IBM.
* There is an assembler bug in versions of DG/UX prior to 5.4.2.01
that occurs when the `fldcr' instruction is used. GNU CC uses
`fldcr' on the 88100 to serialize volatile memory references. Use
the option `-mno-serialize-volatile' if your version of the
assembler has this bug.
* On VMS, GAS versions 1.38.1 and earlier may cause spurious warning
messages from the linker. These warning messages complain of
mismatched psect attributes. You can ignore them. *Note VMS
Install::.
* On NewsOS version 3, if you include both of the files `stddef.h'
and `sys/types.h', you get an error because there are two typedefs
of `size_t'. You should change `sys/types.h' by adding these
lines around the definition of `size_t':
#ifndef _SIZE_T
#define _SIZE_T
ACTUAL TYPEDEF HERE
#endif
* On the Alliant, the system's own convention for returning
structures and unions is unusual, and is not compatible with GNU
CC no matter what options are used.
* On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different
convention for structure and union returning. Use the option
`-mhc-struct-return' to tell GNU CC to use a convention compatible
with it.
* On Ultrix, the Fortran compiler expects registers 2 through 5 to
be saved by function calls. However, the C compiler uses
conventions compatible with BSD Unix: registers 2 through 5 may be
clobbered by function calls.
GNU CC uses the same convention as the Ultrix C compiler. You can
use these options to produce code compatible with the Fortran
compiler:
-fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5
* On the WE32k, you may find that programs compiled with GNU CC do
not work with the standard shared C ilbrary. You may need to link
with the ordinary C compiler. If you do so, you must specify the
following options:
-L/usr/local/lib/gcc-lib/we32k-att-sysv/2.6.0 -lgcc -lc_s
The first specifies where to find the library `libgcc.a' specified
with the `-lgcc' option.
GNU CC does linking by invoking `ld', just as `cc' does, and there
is no reason why it *should* matter which compilation program you
use to invoke `ld'. If someone tracks this problem down, it can
probably be fixed easily.
* On the Alpha, you may get assembler errors about invalid syntax as
a result of floating point constants. This is due to a bug in the
C library functions `ecvt', `fcvt' and `gcvt'. Given valid
floating point numbers, they sometimes print `NaN'.
* On Irix 4.0.5F (and perhaps in some other versions), an assembler
bug sometimes reorders instructions incorrectly when optimization
is turned on. If you think this may be happening to you, try
using the GNU assembler; GAS version 2.1 supports ECOFF on Irix.
Or use the `-noasmopt' option when you compile GNU CC with itself,
and then again when you compile your program. (This is a temporary
kludge to turn off assembler optimization on Irix.) If this
proves to be what you need, edit the assembler spec in the file
`specs' so that it unconditionally passes `-O0' to the assembler,
and never passes `-O2' or `-O3'.