gcc.texi

GCC

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

For C++ programs, GCC 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 GCC 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 @option{-O} for those source files.
@end ignore

@item
On some SGI systems, when you use @option{-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 GCC.
You must specify all three options explicitly.

@item
On a Sparc, GCC 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 GCC, 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 GCC 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 @option{-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 GCC
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 GCC correctly.  We do not yet know why.  However, GCC
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 GCC.  Specifically, it fails to work on functions that use
@code{alloca} or variable-size arrays.  This is because GCC doesn't
generate HP-UX unwind descriptors for such functions.  It may even be
impossible to generate them.

@item
Debugging (@option{-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 GCC, but is now exceptionally rare.  If you should run
into it, you can work around by making your function smaller.

@item
GCC 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 @option{-g} option in GCC from
working.  Note that @file{Makefile.in} uses @option{-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 presence 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 @option{-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 ISO C.

@item
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 (@samp{.} vs @samp{,} 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 @env{LANG} environment variable to
@samp{C} or @samp{En_US}.

@item
@opindex fdollars-in-identifiers
Even if you specify @option{-fdollars-in-identifiers},
you cannot successfully use @samp{$} in identifiers on the RS/6000 due
to a restriction in the IBM assembler.  GAS supports these
identifiers.

@item
On the RS/6000, XLC version 1.3.0.0 will miscompile @file{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.

@item
@opindex mno-serialize-volatile
There is an assembler bug in versions of DG/UX prior to 5.4.2.01 that
occurs when the @samp{fldcr} instruction is used.  GCC uses
@samp{fldcr} on the 88100 to serialize volatile memory references.  Use
the option @option{-mno-serialize-volatile} if your version of the
assembler has this bug.

@item
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.  @xref{VMS Install}.

@item
On NewsOS version 3, if you include both of the files @file{stddef.h}
and @file{sys/types.h}, you get an error because there are two typedefs
of @code{size_t}.  You should change @file{sys/types.h} by adding these
lines around the definition of @code{size_t}:

@smallexample
#ifndef _SIZE_T
#define _SIZE_T
@var{actual-typedef-here}
#endif
@end smallexample

@cindex Alliant
@item
On the Alliant, the system's own convention for returning structures
and unions is unusual, and is not compatible with GCC no matter
what options are used.

@cindex RT PC
@cindex IBM RT PC
@item
@opindex mhc-struct-return
On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different
convention for structure and union returning.  Use the option
@option{-mhc-struct-return} to tell GCC to use a convention compatible
with it.

@cindex Vax calling convention
@cindex Ultrix calling convention
@item
@opindex fcall-saved
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.

GCC uses the same convention as the Ultrix C compiler.  You can use
these options to produce code compatible with the Fortran compiler:

@smallexample
-fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5
@end smallexample

@item
On the WE32k, you may find that programs compiled with GCC do not
work with the standard shared C library.  You may need to link with
the ordinary C compiler.  If you do so, you must specify the following
options:

@smallexample
-L/usr/local/lib/gcc-lib/we32k-att-sysv/2.8.1 -lgcc -lc_s
@end smallexample

The first specifies where to find the library @file{libgcc.a}
specified with the @option{-lgcc} option.

GCC does linking by invoking @command{ld}, just as @command{cc} does, and
there is no reason why it @emph{should} matter which compilation program
you use to invoke @command{ld}.  If someone tracks this problem down,
it can probably be fixed easily.

@item
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 @code{ecvt}, @code{fcvt} and @code{gcvt}.  Given valid
floating point numbers, they sometimes print @samp{NaN}.

@item
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.

@opindex noasmopt
Or use the @option{-noasmopt} option when you compile GCC 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 @file{specs} so
that it unconditionally passes @option{-O0} to the assembler, and never
passes @option{-O2} or @option{-O3}.
@end itemize

@node External Bugs
@section Problems Compiling Certain Programs

@c prevent bad page break with this line
Certain programs have problems compiling.

@itemize @bullet
@item
Parse errors may occur compiling X11 on a Decstation running Ultrix 4.2
because of problems in DEC's versions of the X11 header files
@file{X11/Xlib.h} and @file{X11/Xutil.h}.  People recommend adding
@option{-I/usr/include/mit} to use the MIT versions of the header files,
using the @option{-traditional} switch to turn off ISO C, or fixing the
header files by adding this:

@example
#ifdef __STDC__
#define NeedFunctionPrototypes 0
#endif
@end example

@item
On various 386 Unix systems derived from System V, including SCO, ISC,
and ESIX, you may get error messages about running out of virtual memory
while compiling certain programs.

You can prevent this problem by linking GCC with the GNU malloc