This section lists various difficulties encountered in using GCC together with other compilers or with the assemblers, linkers, libraries and debuggers on certain systems.
On many platforms, GCC supports a different ABI for C++ than do other compilers, so the object files compiled by GCC cannot be used with object files generated by another C++ compiler.
An area where the difference is most apparent is name mangling. The use of different name mangling 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 compilersbut the programs would then crash when run. Incompatible libraries are then detected at link time, rather than at run time.
causes static variable destructors (currently used only in C++) not to be run.
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 GCC, dereferencing the pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program with GCC. 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.
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 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.
with GCC. Specifically, it fails to work on functions that use alloca or variable-size arrays. This is because GCC doesnt generate HP-UX unwind descriptors for such functions. It may even be impossible to generate them.
the preliminary GNU tools.
PA assembler. GAS for the PA does not have this problem.
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.
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.
the form:
(warning) Use of GR3 when
frame >= 8192 may cause conflict.
These warnings are harmless and can be safely ignored.
receive errors from the AIX Assembler complaining about a displacement that is too large. If you should run into it, you can work around by making your function smaller.
linker semantics which merges global symbols between libraries and applications, especially necessary for C++ streams functionality. This is not the default behavior of AIX shared libraries and dynamic linking. libstdc++.a is built on AIX with runtime-linking enabled so that symbol merging can occur. To utilize this feature, the application linked with libstdc++.a must include the -Wl,-brtl flag on the link line. G++ cannot impose this because this option may interfere with the semantics of the user program and users may not always use g++ to link his or her application. Applications are not required to use the -Wl,-brtl flag on the link linethe rest of the libstdc++.a library which is not dependent on the symbol merging semantics will continue to function correctly.
functions invoked by libstdc++.a with runtime-linking enabled on AIX. To accomplish this the application must be linked with runtime-linking option and the functions explicitly must be exported by the application (-Wl,-brtl,-bE:exportfile).
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.