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199 lines
9.9 KiB
HTML
199 lines
9.9 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Interoperation - Using the GNU Compiler Collection (GCC)</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Trouble.html#Trouble" title="Trouble">
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<link rel="prev" href="Actual-Bugs.html#Actual-Bugs" title="Actual Bugs">
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<link rel="next" href="Incompatibilities.html#Incompatibilities" title="Incompatibilities">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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<style type="text/css"><!--
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Interoperation"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Incompatibilities.html#Incompatibilities">Incompatibilities</a>,
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Previous: <a rel="previous" accesskey="p" href="Actual-Bugs.html#Actual-Bugs">Actual Bugs</a>,
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Up: <a rel="up" accesskey="u" href="Trouble.html#Trouble">Trouble</a>
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<hr>
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</div>
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<h3 class="section">12.2 Interoperation</h3>
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<p>This section lists various difficulties encountered in using GCC
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together with other compilers or with the assemblers, linkers,
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libraries and debuggers on certain systems.
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<ul>
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<li>On many platforms, GCC supports a different ABI for C++ than do other
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compilers, so the object files compiled by GCC cannot be used with object
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files generated by another C++ compiler.
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<p>An area where the difference is most apparent is name mangling. The use
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of different name mangling is intentional, to protect you from more subtle
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problems.
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Compilers differ as to many internal details of C++ implementation,
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including: how class instances are laid out, how multiple inheritance is
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implemented, and how virtual function calls are handled. If the name
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encoding were made the same, your programs would link against libraries
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provided from other compilers—but the programs would then crash when
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run. Incompatible libraries are then detected at link time, rather than
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at run time.
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<li>On some BSD systems, including some versions of Ultrix, use of profiling
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causes static variable destructors (currently used only in C++) not to
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be run.
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<li>On a SPARC, GCC aligns all values of type <code>double</code> on an 8-byte
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boundary, and it expects every <code>double</code> to be so aligned. The Sun
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compiler usually gives <code>double</code> values 8-byte alignment, with one
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exception: function arguments of type <code>double</code> may not be aligned.
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<p>As a result, if a function compiled with Sun CC takes the address of an
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argument of type <code>double</code> and passes this pointer of type
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<code>double *</code> to a function compiled with GCC, dereferencing the
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pointer may cause a fatal signal.
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<p>One way to solve this problem is to compile your entire program with GCC.
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Another solution is to modify the function that is compiled with
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Sun CC to copy the argument into a local variable; local variables
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are always properly aligned. A third solution is to modify the function
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that uses the pointer to dereference it via the following function
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<code>access_double</code> instead of directly with ‘<samp><span class="samp">*</span></samp>’:
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<pre class="smallexample"> inline double
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access_double (double *unaligned_ptr)
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{
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union d2i { double d; int i[2]; };
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union d2i *p = (union d2i *) unaligned_ptr;
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union d2i u;
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u.i[0] = p->i[0];
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u.i[1] = p->i[1];
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return u.d;
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}
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</pre>
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<p class="noindent">Storing into the pointer can be done likewise with the same union.
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<li>On Solaris, the <code>malloc</code> function in the <samp><span class="file">libmalloc.a</span></samp> library
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may allocate memory that is only 4 byte aligned. Since GCC on the
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SPARC assumes that doubles are 8 byte aligned, this may result in a
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fatal signal if doubles are stored in memory allocated by the
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<samp><span class="file">libmalloc.a</span></samp> library.
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<p>The solution is to not use the <samp><span class="file">libmalloc.a</span></samp> library. Use instead
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<code>malloc</code> and related functions from <samp><span class="file">libc.a</span></samp>; they do not have
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this problem.
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<li>On the HP PA machine, ADB sometimes fails to work on functions compiled
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with GCC. Specifically, it fails to work on functions that use
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<code>alloca</code> or variable-size arrays. This is because GCC doesn't
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generate HP-UX unwind descriptors for such functions. It may even be
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impossible to generate them.
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<li>Debugging (<samp><span class="option">-g</span></samp>) is not supported on the HP PA machine, unless you use
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the preliminary GNU tools.
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<li>Taking the address of a label may generate errors from the HP-UX
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PA assembler. GAS for the PA does not have this problem.
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<li>Using floating point parameters for indirect calls to static functions
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will not work when using the HP assembler. There simply is no way for GCC
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to specify what registers hold arguments for static functions when using
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the HP assembler. GAS for the PA does not have this problem.
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<li>In extremely rare cases involving some very large functions you may
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receive errors from the HP linker complaining about an out of bounds
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unconditional branch offset. This used to occur more often in previous
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versions of GCC, but is now exceptionally rare. If you should run
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into it, you can work around by making your function smaller.
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<li>GCC compiled code sometimes emits warnings from the HP-UX assembler of
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the form:
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<pre class="smallexample"> (warning) Use of GR3 when
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frame >= 8192 may cause conflict.
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</pre>
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<p>These warnings are harmless and can be safely ignored.
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<li>In extremely rare cases involving some very large functions you may
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receive errors from the AIX Assembler complaining about a displacement
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that is too large. If you should run into it, you can work around by
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making your function smaller.
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<li>The <samp><span class="file">libstdc++.a</span></samp> library in GCC relies on the SVR4 dynamic
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linker semantics which merges global symbols between libraries and
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applications, especially necessary for C++ streams functionality.
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This is not the default behavior of AIX shared libraries and dynamic
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linking. <samp><span class="file">libstdc++.a</span></samp> is built on AIX with “runtime-linking”
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enabled so that symbol merging can occur. To utilize this feature,
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the application linked with <samp><span class="file">libstdc++.a</span></samp> must include the
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<samp><span class="option">-Wl,-brtl</span></samp> flag on the link line. G++ cannot impose this
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because this option may interfere with the semantics of the user
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program and users may not always use ‘<samp><span class="samp">g++</span></samp>’ to link his or her
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application. Applications are not required to use the
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<samp><span class="option">-Wl,-brtl</span></samp> flag on the link line—the rest of the
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<samp><span class="file">libstdc++.a</span></samp> library which is not dependent on the symbol
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merging semantics will continue to function correctly.
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<li>An application can interpose its own definition of functions for
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functions invoked by <samp><span class="file">libstdc++.a</span></samp> with “runtime-linking”
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enabled on AIX. To accomplish this the application must be linked
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with “runtime-linking” option and the functions explicitly must be
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exported by the application (<samp><span class="option">-Wl,-brtl,-bE:exportfile</span></samp>).
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<li>AIX on the RS/6000 provides support (NLS) for environments outside of
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the United States. Compilers and assemblers use NLS to support
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locale-specific representations of various objects including
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floating-point numbers (‘<samp><span class="samp">.</span></samp>’ vs ‘<samp><span class="samp">,</span></samp>’ for separating decimal
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fractions). There have been problems reported where the library linked
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with GCC does not produce the same floating-point formats that the
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assembler accepts. If you have this problem, set the <samp><span class="env">LANG</span></samp>
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environment variable to ‘<samp><span class="samp">C</span></samp>’ or ‘<samp><span class="samp">En_US</span></samp>’.
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<li><a name="index-fdollars_002din_002didentifiers-4244"></a>Even if you specify <samp><span class="option">-fdollars-in-identifiers</span></samp>,
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you cannot successfully use ‘<samp><span class="samp">$</span></samp>’ in identifiers on the RS/6000 due
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to a restriction in the IBM assembler. GAS supports these
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identifiers.
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</ul>
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</body></html>
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