gcc.texi

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@file{iclib.a}.  You must also modify @file{stdio.h} as follows: before
the lines

@example
#if     defined(__i860__) && !defined(_VA_LIST)
#include <va_list.h>
@end example

@noindent
insert the line

@example
#if __PGC__
@end example

@noindent
and after the lines

@example
extern int  vprintf(const char *, va_list );
extern int  vsprintf(char *, const char *, va_list );
#endif
@end example

@noindent
insert the line

@example
#endif /* __PGC__ */
@end example

These problems don't exist in operating system version 1.1.

@item
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
@file{README.ALTOS}.

@item
You will get several sorts of compilation and linking errors on the
we32k if you don't follow the special instructions.  @xref{Configurations}.

@item
A bug in the HP-UX 8.05 (and earlier) shell will cause the fixproto
program to report an error of the form:

@example
./fixproto: sh internal 1K buffer overflow
@end example

To fix this, change the first line of the fixproto script to look like:

@example
#!/bin/ksh
@end example
@end itemize

@node Cross-Compiler Problems
@section Cross-Compiler Problems

You may run into problems with cross compilation on certain machines,
for several reasons.

@itemize @bullet
@item
Cross compilation can run into trouble for certain machines because
some target machines' assemblers require floating point numbers to be
written as @emph{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 @code{REAL_VALUE_TYPE}.  But doing so is a substantial amount of
work for each target machine.
@ifset INTERNALS
@xref{Cross-compilation}.
@end ifset
@ifclear INTERNALS
@xref{Cross-compilation,,Cross Compilation and Floating Point Format,
gcc.info, Using and Porting GCC}.
@end ifclear

@item
At present, the program @file{mips-tfile} which adds debug
support to object files on MIPS systems does not work in a cross
compile environment.
@end itemize

@node Interoperation
@section 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.

@itemize @bullet
@item
Objective C does not work on the RS/6000.

@item
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.

@item
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.

@item
@cindex DBX
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.

@item
The GNU assembler (GAS) does not support PIC.  To generate PIC code, you
must use some other assembler, such as @file{/bin/as}.

@item
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.

@item
Use of @samp{-I/usr/include} may cause trouble.

Many systems come with header files that won't work with GNU CC unless
corrected by @code{fixincludes}.  The corrected header files go in a new
directory; GNU CC searches this directory before @file{/usr/include}.
If you use @samp{-I/usr/include}, this tells GNU CC to search
@file{/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):

@smallexample
-I/usr/local/lib/gcc-lib/@var{target}/@var{version}/include -I/usr/include
@end smallexample

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 @emph{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:

@example
-I/usr/local/lib/g++-include
@end example

@ignore
@cindex @code{vfork}, for the Sun-4
@item
There is a bug in @code{vfork} on the Sun-4 which causes the registers
of the child process to clobber those of the parent.  Because of this,
programs that call @code{vfork} are likely to lose when compiled
optimized with GNU CC when the child code alters registers which contain
C variables in the parent.  This affects variables which are live in the
parent across the call to @code{vfork}.

If you encounter this, you can work around the problem by declaring
variables @code{volatile} in the function that calls @code{vfork}, until
the problem goes away, or by not declaring them @code{register} and not
using @samp{-O} for those source files.
@end ignore

@item
On some SGI systems, when you use @samp{-lgl_s} as an option,
it gets translated magically to @samp{-lgl_s -lX11_s -lc_s}.
Naturally, this does not happen when you use GNU CC.
You must specify all three options explicitly.

@item
On a Sparc, GNU CC aligns all values of type @code{double} on an 8-byte
boundary, and it expects every @code{double} to be so aligned.  The Sun
compiler usually gives @code{double} values 8-byte alignment, with one
exception: function arguments of type @code{double} may not be aligned.

As a result, if a function compiled with Sun CC takes the address of an
argument of type @code{double} and passes this pointer of type
@code{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
@code{access_double} instead of directly with @samp{*}:

@smallexample
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;
@}
@end smallexample

@noindent
Storing into the pointer can be done likewise with the same union.

@item
On Solaris, the @code{malloc} function in the @file{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
@file{libmalloc.a} library.

The solution is to not use the @file{libmalloc.a} library.  Use instead
@code{malloc} and related functions from @file{libc.a}; they do not have
this problem.

@item
Sun forgot to include a static version of @file{libdl.a} with some
versions of SunOS (mainly 4.1).  This results in undefined symbols when
linking static binaries (that is, if you use @samp{-static}).  If you
see undefined symbols @code{_dlclose}, @code{_dlsym} or @code{_dlopen}
when linking, compile and link against the file
@file{mit/util/misc/dlsym.c} from the MIT version of X windows.

@item
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 emulator uses an obsolete and incompatible format.  Long doubles
do not work in Sun OS version 4.1.1 due to a problem in a Sun library.
Long doubles do work on Sun OS versions 4.1.2 and higher, but GNU CC
does not enable them by default.  Long doubles appear to work in Sun OS
5.x (Solaris 2.x).

@item
On HP-UX version 9.01 on the HP PA, the HP compiler @code{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.

@item
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
@code{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.

@item
Debugging (@samp{-g}) is not supported on the HP PA machine, unless you use
the preliminary GNU tools (@pxref{Installation}).

@item
Taking the address of a label may generate errors from the HP-UX
PA assembler.  GAS for the PA does not have this problem.

@item
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.

@item
In extremely rare cases involving some very large functions you may
receive errors from the HP linker complaining about an out of bounds
unconditional branch offset.  This used to occur more often in previous
versions of GNU CC, but is now exceptionally rare.  If you should run
into it, you can work around by making your function smaller.

@item
GNU CC compiled code sometimes emits warnings from the HP-UX assembler of
the form:

@smallexample
(warning) Use of GR3 when
  frame >= 8192 may cause conflict.
@end smallexample

These warnings are harmless and can be safely ignored.

@item
The current version of the assembler (@file{/bin/as}) for the RS/6000
has certain problems that prevent the @samp{-g} option in GCC from
working.  Note that @file{Makefile.in} uses @samp{-g} by default when
compiling @file{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 @file{README.RS6000} for more details on these updates.

You can test for the presense of a fixed assembler by using the
command

@smallexample
as -u < /dev/null
@end smallexample

@noindent
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.

@item
On the IBM RS/6000, compiling code of the form

@smallexample
extern int foo;

@dots{} foo @dots{}

static int foo;
@end smallexample

@noindent
will cause the linker to report an undefined symbol @code{foo}.
Although this behavior differs from most other systems, it is not a
bug because redefining an @code{extern} variable as @code{static}
is undefined in ANSI C.

@item