| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being "Funding Free Software", the Front-Cover |
| Texts being (a) (see below), and with the Back-Cover Texts being (b) |
| (see below). A copy of the license is included in the section entitled |
| "GNU Free Documentation License". |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Using the GNU Compiler Collection (GCC): Interoperation</title> |
| |
| <meta name="description" content="Using the GNU Compiler Collection (GCC): Interoperation"> |
| <meta name="keywords" content="Using the GNU Compiler Collection (GCC): Interoperation"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Trouble.html#Trouble" rel="up" title="Trouble"> |
| <link href="Incompatibilities.html#Incompatibilities" rel="next" title="Incompatibilities"> |
| <link href="Actual-Bugs.html#Actual-Bugs" rel="prev" title="Actual Bugs"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Interoperation"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Incompatibilities.html#Incompatibilities" accesskey="n" rel="next">Incompatibilities</a>, Previous: <a href="Actual-Bugs.html#Actual-Bugs" accesskey="p" rel="prev">Actual Bugs</a>, Up: <a href="Trouble.html#Trouble" accesskey="u" rel="up">Trouble</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Interoperation-1"></a> |
| <h3 class="section">11.2 Interoperation</h3> |
| |
| <p>This section lists various difficulties encountered in using GCC |
| together with other compilers or with the assemblers, linkers, |
| libraries and debuggers on certain systems. |
| </p> |
| <ul> |
| <li> 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. |
| |
| <p>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 compilers—but the programs would then crash when |
| run. Incompatible libraries are then detected at link time, rather than |
| at run time. |
| </p> |
| </li><li> 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. |
| |
| </li><li> On a SPARC, GCC aligns all values of type <code>double</code> on an 8-byte |
| boundary, and it expects every <code>double</code> to be so aligned. The Sun |
| compiler usually gives <code>double</code> values 8-byte alignment, with one |
| exception: function arguments of type <code>double</code> may not be aligned. |
| |
| <p>As a result, if a function compiled with Sun CC takes the address of an |
| argument of type <code>double</code> and passes this pointer of type |
| <code>double *</code> to a function compiled with GCC, dereferencing the |
| pointer may cause a fatal signal. |
| </p> |
| <p>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 |
| <code>access_double</code> instead of directly with ‘<samp>*</samp>’: |
| </p> |
| <div class="smallexample"> |
| <pre class="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; |
| } |
| </pre></div> |
| |
| <p>Storing into the pointer can be done likewise with the same union. |
| </p> |
| </li><li> On Solaris, the <code>malloc</code> function in the <samp>libmalloc.a</samp> 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 |
| <samp>libmalloc.a</samp> library. |
| |
| <p>The solution is to not use the <samp>libmalloc.a</samp> library. Use instead |
| <code>malloc</code> and related functions from <samp>libc.a</samp>; they do not have |
| this problem. |
| </p> |
| </li><li> 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</code> 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. |
| |
| </li><li> Debugging (<samp>-g</samp>) is not supported on the HP PA machine, unless you use |
| the preliminary GNU tools. |
| |
| </li><li> Taking the address of a label may generate errors from the HP-UX |
| PA assembler. GAS for the PA does not have this problem. |
| |
| </li><li> 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. |
| |
| </li><li> 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. |
| |
| </li><li> GCC compiled code sometimes emits warnings from the HP-UX assembler of |
| the form: |
| |
| <div class="smallexample"> |
| <pre class="smallexample">(warning) Use of GR3 when |
| frame >= 8192 may cause conflict. |
| </pre></div> |
| |
| <p>These warnings are harmless and can be safely ignored. |
| </p> |
| </li><li> In extremely rare cases involving some very large functions you may |
| 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. |
| |
| </li><li> The <samp>libstdc++.a</samp> library in GCC relies on the SVR4 dynamic |
| 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. <samp>libstdc++.a</samp> is built on AIX with “runtime-linking” |
| enabled so that symbol merging can occur. To utilize this feature, |
| the application linked with <samp>libstdc++.a</samp> must include the |
| <samp>-Wl,-brtl</samp> 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 ‘<samp>g++</samp>’ to link his or her |
| application. Applications are not required to use the |
| <samp>-Wl,-brtl</samp> flag on the link line—the rest of the |
| <samp>libstdc++.a</samp> library which is not dependent on the symbol |
| merging semantics will continue to function correctly. |
| |
| </li><li> An application can interpose its own definition of functions for |
| functions invoked by <samp>libstdc++.a</samp> 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 (<samp>-Wl,-brtl,-bE:exportfile</samp>). |
| |
| </li><li> 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>.</samp>’ vs ‘<samp>,</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 <code>LANG</code> |
| environment variable to ‘<samp>C</samp>’ or ‘<samp>En_US</samp>’. |
| |
| </li><li> <a name="index-fdollars_002din_002didentifiers-1"></a> |
| Even if you specify <samp>-fdollars-in-identifiers</samp>, |
| you cannot successfully use ‘<samp>$</samp>’ in identifiers on the RS/6000 due |
| to a restriction in the IBM assembler. GAS supports these |
| identifiers. |
| |
| </li></ul> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Incompatibilities.html#Incompatibilities" accesskey="n" rel="next">Incompatibilities</a>, Previous: <a href="Actual-Bugs.html#Actual-Bugs" accesskey="p" rel="prev">Actual Bugs</a>, Up: <a href="Trouble.html#Trouble" accesskey="u" rel="up">Trouble</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
