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| |
| <section id="integrating-with-newlib"> |
| <h1>Integrating with Newlib<a class="headerlink" href="#integrating-with-newlib" title="Permalink to this heading"></a></h1> |
| <div class="admonition warning"> |
| <p class="admonition-title">Warning</p> |
| <p>Migrated from: |
| <a class="reference external" href="https://cwiki.apache.org/confluence/display/NUTTX/Integrating+with+Newlib">https://cwiki.apache.org/confluence/display/NUTTX/Integrating+with+Newlib</a></p> |
| </div> |
| <section id="built-in-c-library"> |
| <h2>Built-In C Library<a class="headerlink" href="#built-in-c-library" title="Permalink to this heading"></a></h2> |
| <p>NuttX has its own, tiny, built-in C library. Along with that C library are |
| all of the headers files with the definitions specific to that built-in C |
| library. The definitions in those header files are not compatible with the |
| definitions that you will find in the header files that come with any other |
| C library and trying to mix these with header files from other C libraries |
| is bound to cause you problems.</p> |
| <p>When GCC is built, it is built against a C library. The NuttX <cite>buildroot</cite> |
| tools are, of course, built against the built-in NuttX C-library and |
| would seem to be the obvious choice of tools to use. But there are |
| many reasons to use other tool chains. As examples, the NuttX <cite>buildroot</cite> |
| tools have some limitations in C++ support. Another example, is that you |
| might want to use the higher-performance math library that is included |
| in some other implementation of the C library.</p> |
| <p>There are many C libraries available: <cite>glibc</cite> and <cite>uClibc</cite> are commonly |
| used with Linux tools. These should be avoided. Most embedded toolchains |
| will be built against <cite>newlib</cite>. So if you are not using the NuttX buildroot |
| toolchain, you will most likely be using a toolchain that has <cite>newlib</cite> built |
| into it. Because of this, you may see issues if you include <cite>newlib</cite> header |
| files into your NuttX code.</p> |
| </section> |
| <section id="header-file-issues"> |
| <h2>Header File Issues<a class="headerlink" href="#header-file-issues" title="Permalink to this heading"></a></h2> |
| <section id="math-h"> |
| <h3>math.h<a class="headerlink" href="#math-h" title="Permalink to this heading"></a></h3> |
| <p>Nuttx includes a built-in math library that can be selected with |
| <code class="docutils literal notranslate"><span class="pre">CONFIG_LIBM=y</span></code>. There are reasons to use an external math library, |
| however: The NuttX math library is written in C and will not be as |
| performant as a custom math library tuned for your processor |
| architecture. There some addition issues with the NuttX math |
| libraries as documented in the top-level TODO list.</p> |
| <p>Many people choose to use the <cite>newlib</cite> math library. If you include |
| <code class="docutils literal notranslate"><span class="pre">math.h</span></code> without selecting <code class="docutils literal notranslate"><span class="pre">CONFIG_LIBM=y</span></code>, you will probably get the |
| <cite>newlib</cite> math library and you will certainly see a compilation error |
| involving the definition of the type <code class="docutils literal notranslate"><span class="pre">wint_t</span></code>.</p> |
| <p>There have been many work arounds described in the NuttX forum. |
| Here are a few:</p> |
| <ul class="simple"> |
| <li><p>Copy the newlib <code class="docutils literal notranslate"><span class="pre">math.h</span></code> to <code class="docutils literal notranslate"><span class="pre">nuttx/include/math.h</span></code> and remove |
| the reference to <code class="docutils literal notranslate"><span class="pre">wint_t</span></code>.</p></li> |
| <li><p>Add the following to <code class="docutils literal notranslate"><span class="pre">nuttx/libc/stdio/lib_libvsprintf.c</span></code>. I |
| especially dislike this solution because it involves modification |
| to a NuttX header file that cannot be accepted upstream.</p></li> |
| </ul> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cm">/* Include floating point functions */</span> |
| |
| <span class="cp">#ifdef CONFIG_LIBC_FLOATINGPOINT</span> |
| <span class="cp">#</span><span class="w"> </span><span class="cp">include</span><span class="w"> </span><span class="cpf">"wchar.h"</span> |
| <span class="cp">#</span><span class="w"> </span><span class="cp">include</span><span class="w"> </span><span class="cpf">"stdio/lib_libdtoa.c"</span> |
| <span class="cp">#endif</span> |
| </pre></div> |
| </div> |
| <ul class="simple"> |
| <li><p>Provide your own version of <code class="docutils literal notranslate"><span class="pre">math.h</span></code> (for GCC only) containing the |
| following. And add the path to this <code class="docutils literal notranslate"><span class="pre">math.h</span></code> to your <code class="docutils literal notranslate"><span class="pre">CFLAGS</span></code> include |
| path arguments. The path can specified by adding <code class="docutils literal notranslate"><span class="pre">-system</span></code> or <code class="docutils literal notranslate"><span class="pre">-I</span></code> to the |
| CFLAGS. The path to this <code class="docutils literal notranslate"><span class="pre">math.h</span></code> must be defined last so that it has |
| precedence. This will include the NuttX <code class="docutils literal notranslate"><span class="pre">wint_t</span></code> definition, then continue |
| to include the default version of <code class="docutils literal notranslate"><span class="pre">math.h</span></code>.</p></li> |
| </ul> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#ifndef _MYMATH_H</span> |
| <span class="cp">#define _MYMATH_H</span> |
| |
| <span class="cp">#include</span><span class="w"> </span><span class="cpf">"wchar.h"</span> |
| <span class="cp">#include_next <math.h></span> |
| |
| <span class="cp">#endif </span><span class="cm">/* _MYMATH_H */</span> |
| </pre></div> |
| </div> |
| <ul class="simple"> |
| <li><p>The PX4 team uses these patches to <a class="reference external" href="https://github.com/PX4/Firmware/blob/nuttx_v3/nuttx-patches/c%2B%2B11.patch">cwhar</a> |
| and <a class="reference external" href="https://github.com/PX4/Firmware/blob/nuttx_v3/nuttx-patches/math.h.patch">math.h</a> |
| to solve the issue. But note the comments in that code:</p></li> |
| </ul> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="cm">/* N.B. The following definitions are enabled at this time to allow the PX4</span> |
| <span class="cm">* development to continue until there is a SAFE solution to foreign</span> |
| <span class="cm">* (non-nuttx) header file inclusion. There is a potential of a binary</span> |
| <span class="cm">* incompatibility and runtime errors, memory overwrites or corruption</span> |
| <span class="cm">* VVVVVVVVVVVVVVVVVVVVVVVVVV Begin Warning VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV</span> |
| <span class="cm">*/</span> |
| </pre></div> |
| </div> |
| <ul class="simple"> |
| <li><p>Some people have suggested adding the type definition of <code class="docutils literal notranslate"><span class="pre">wint_t</span></code> to |
| <code class="docutils literal notranslate"><span class="pre">nuttx/include/sys/types.h</span></code> merely because that header file will then |
| be included into the newlib <code class="docutils literal notranslate"><span class="pre">math.h</span></code>. This inclusion, of course, also |
| <cite>very dangerous</cite> since the types in the NuttX <code class="docutils literal notranslate"><span class="pre">sys/types.h</span></code> header file |
| may not agree with the types in the pre-compiled newlib math library. |
| This solution is not recommended, in any case. The type <code class="docutils literal notranslate"><span class="pre">wint_t</span></code> is |
| already correctly defined in <code class="docutils literal notranslate"><span class="pre">nuttx/include/sys/wchar.h</span></code> which is the |
| one and only correct location per |
| <a class="reference external" href="http://pubs.opengroup.org/onlinepubs/007908775/xsh/wchar.h.html">OpenGroup.org</a>. |
| It is a mystery to me why the newlib <code class="docutils literal notranslate"><span class="pre">math.h</span></code> header file uses <code class="docutils literal notranslate"><span class="pre">wint_t</span></code> |
| without including <code class="docutils literal notranslate"><span class="pre">wchar.h</span></code>. If it did, then there would then this |
| compilation issue would not exist |
| (there could still be subtle binary compatibility issues).</p></li> |
| <li><p>The ideal solution would be to integrate a third-party, optimized, |
| ARM math library into NuttX, building it using only NuttX header |
| files. That would guarantee no binary incompatibility and would be |
| a very useful contribution to NuttX.</p></li> |
| </ul> |
| <p>Changes to the <code class="docutils literal notranslate"><span class="pre">nuttx/arch/<architecture>/src/Makefile</span></code> may also be required so |
| that the linker can find and include the math library (similar to the existed |
| logic in the <code class="docutils literal notranslate"><span class="pre">Makefile</span></code> to find <code class="docutils literal notranslate"><span class="pre">libgcc.a</span></code>).</p> |
| <p>Update: This issue may have finally been resolved with this commit:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>commit 894ca622e6a408e5fa858a3fee46fb16f32cf86c |
| Author: Xiang Xiao \<xiaoxiang@xiaomi.com\> |
| Date: Mon Aug 27 06:26:37 2018 -0600 |
| |
| include/sys/types: Move wint_t and wctype_t from wchar.h to |
| types.h. This change is compatible as before since wchar.h |
| include types.h indirectly. This fixes a compilation error with |
| newlib's math.h: 'unknown type name wint_t' |
| </pre></div> |
| </div> |
| </section> |
| <section id="cmath"> |
| <h3>cmath<a class="headerlink" href="#cmath" title="Permalink to this heading"></a></h3> |
| <p>This error has been reported:</p> |
| <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>/nuttx/include/cxx/cmath:124:11:<span class="w"> </span>error:<span class="w"> </span><span class="s1">'::log2l'</span><span class="w"> </span>has<span class="w"> </span>not<span class="w"> </span>been<span class="w"> </span>declared... |
| </pre></div> |
| </div> |
| <p>Apparently the function logic <code class="docutils literal notranslate"><span class="pre">log2l()</span></code> is defined in the NuttX <code class="docutils literal notranslate"><span class="pre">math.h</span></code> and |
| added to the <code class="docutils literal notranslate"><span class="pre">std::</span></code> namespace in <code class="docutils literal notranslate"><span class="pre">cmath</span></code>. But, apparently, the |
| newlib <code class="docutils literal notranslate"><span class="pre">math.h</span></code> does not prototype <code class="docutils literal notranslate"><span class="pre">lib2l()</span></code>.</p> |
| <p>If you plan to use the newlib <code class="docutils literal notranslate"><span class="pre">math.h</span></code> and the NuttX <code class="docutils literal notranslate"><span class="pre">cmath</span></code>, then |
| you probably have to modify <code class="docutils literal notranslate"><span class="pre">cmath</span></code> as well.</p> |
| </section> |
| <section id="alloca-h"> |
| <h3>alloca.h<a class="headerlink" href="#alloca-h" title="Permalink to this heading"></a></h3> |
| <p>If your imported application includes <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code>, then you will run into the |
| same kinds of issues. Nuttx does not provide this header file an so you will |
| probably end up including the newlib version of <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code> which has similar |
| disastrous results.</p> |
| <p>One solution for GCC (only) would be to provide you own <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code> containing:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="cp">#ifndef _ALLOCA_H</span> |
| <span class="cp">#define _ALLOCA_H</span> |
| |
| <span class="cp">#define alloca __builtin_alloca</span> |
| |
| <span class="cp">#endif </span><span class="cm">/* _ALLOCA_H */</span> |
| </pre></div> |
| </div> |
| <p>And add the path to this <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code> to your <code class="docutils literal notranslate"><span class="pre">CFLAG</span></code> include path arguments. |
| The path can specified by adding <code class="docutils literal notranslate"><span class="pre">-system</span></code> or <code class="docutils literal notranslate"><span class="pre">-I</span></code> to the CFLAGS. The path |
| to this <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code> must be defined last so that it has precedence.</p> |
| <p>However, if you include newlib header files that include other <code class="docutils literal notranslate"><span class="pre">alloc.h</span></code> |
| you may still end up including the newlib <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code>. So another solution |
| might be to include your own <code class="docutils literal notranslate"><span class="pre">math.h</span></code>, for example, which contains |
| something like like:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="cp">#ifndef _MYMATH_H</span> |
| <span class="cp">#define _MYMATH_H</span> |
| <span class="cp">#ifndef _ALLOCA_H</span> |
| <span class="cp">#define _ALLOCA_H</span> |
| |
| <span class="cp">#define alloca __builtin_alloca</span> |
| |
| <span class="cp">#endif </span><span class="cm">/* _ALLOCA_H */</span> |
| |
| <span class="cp">#include_next <math.h></span> |
| |
| <span class="cp">#endif </span><span class="cm">/* _MYMATH_H */</span> |
| </pre></div> |
| </div> |
| <p>This will provide the <code class="docutils literal notranslate"><span class="pre">alloca()</span></code> definition, then continue to include |
| the default version of <code class="docutils literal notranslate"><span class="pre">math.h</span></code>. This works because the idempotence |
| pre-processor variable <code class="docutils literal notranslate"><span class="pre">_ALLOC_H</span></code> matches the same idempotence variable |
| used in the newlib <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code>. Thus, any sneak inclusion of <code class="docutils literal notranslate"><span class="pre">alloca.h</span></code> |
| with have not effect.</p> |
| </section> |
| </section> |
| <section id="c-issues"> |
| <h2>C++ Issues<a class="headerlink" href="#c-issues" title="Permalink to this heading"></a></h2> |
| <p>Most of the C++ issues that have not so much to do with header |
| files as with C++ name mangling and strict typing.</p> |
| <section id="new-operator"> |
| <h3>new Operator<a class="headerlink" href="#new-operator" title="Permalink to this heading"></a></h3> |
| <p>The prototype for the C++ new operator is:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">operator</span><span class="w"> </span><span class="n">new</span><span class="p">(</span><span class="kt">size_t</span><span class="w"> </span><span class="n">nbytes</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>However, <code class="docutils literal notranslate"><span class="pre">size_t</span></code>, in turn, defined to be either <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">long</span></code> or |
| <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">int</span></code> in the toolchain. This differs with different |
| versions of GCC toolchains and has nothing to do with header |
| file inclusion. NuttX supports a configuration option to work |
| around this, change new to either:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="cp">#ifdef CONFIG_CXX_NEWLONG</span> |
| <span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">operator</span><span class="w"> </span><span class="n">new</span><span class="p">(</span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="n">nbytes</span><span class="p">)</span> |
| <span class="cp">#else</span> |
| <span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">operator</span><span class="w"> </span><span class="n">new</span><span class="p">(</span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">nbytes</span><span class="p">)</span> |
| <span class="cp">#endif</span> |
| </pre></div> |
| </div> |
| <p>This C++ name mangling issue has been around for years and varies from |
| GCC compiler to GCC compiler, apparently due to some <cite>newlib</cite> |
| configuration difference.</p> |
| </section> |
| <section id="uint32-t"> |
| <h3>uint32_t<a class="headerlink" href="#uint32-t" title="Permalink to this heading"></a></h3> |
| <p>Similarly, you may find that the definition of <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> in NuttX may |
| be incompatible with your toolchain’s libraries. You may, |
| perhaps, see errors like:</p> |
| <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>error:<span class="w"> </span>redeclaration<span class="w"> </span>of<span class="w"> </span><span class="s1">'typedef long unsigned int std::uint_least32_t'</span> |
| </pre></div> |
| </div> |
| <p>The definition in the ARM header file at <code class="docutils literal notranslate"><span class="pre">nuttx/arch/arm/include/types.h</span></code> is:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">signed</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">_int32_t</span><span class="p">;</span> |
| <span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">_uint32_t</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>On ARM platforms, <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">long</span></code> and <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">int</span></code> are both 32-bit |
| integers so it does not matter which definition you use. But it does matter |
| if you are concerned about the C++ name mangling associated with the use of |
| size_t by your compiler. If you see errors such as the above, then |
| you can replace these type definition to avoid C++ name mangling |
| incompatibilities like:</p> |
| <div class="highlight-C notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">signed</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="n">_int32_t</span><span class="p">;</span> |
| <span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="n">_uint32_t</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>But this now may result in additional problems, now there may be |
| incompatibilities between definition of <code class="docutils literal notranslate"><span class="pre">size_t</span></code> uses in NuttX and the |
| definition of <code class="docutils literal notranslate"><span class="pre">size_t</span></code> used in the libraries.</p> |
| </section> |
| <section id="size-t"> |
| <h3>size_t<a class="headerlink" href="#size-t" title="Permalink to this heading"></a></h3> |
| <p><code class="docutils literal notranslate"><span class="pre">size_t</span></code> should be an integer type wide enough to hold the size of the |
| largest memory object. So <code class="docutils literal notranslate"><span class="pre">size_t</span></code> really depends on the size of the |
| underlying pointer type. For CPUs with 16-bit addressing, for example, |
| the width of <code class="docutils literal notranslate"><span class="pre">size_t</span></code> should be 16-bits; for CPUs with 32-bit addressing, |
| the width should be 32-bits.</p> |
| <p><code class="docutils literal notranslate"><span class="pre">uint32_t</span></code>, of course, should always be 32-bits in width.</p> |
| <p>Using newlib header files, you also encounter incompatibilities between |
| the definitions of some types, the types <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> and <code class="docutils literal notranslate"><span class="pre">size_t</span></code> is often |
| the sources of problems. For example:</p> |
| <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>error:<span class="w"> </span>redeclaration<span class="w"> </span>of<span class="w"> </span><span class="s1">'typedef unsigned int std::size_t'</span> |
| </pre></div> |
| </div> |
| <p>The root cause of this issue is that the community cannot decide on |
| the correct definition of <code class="docutils literal notranslate"><span class="pre">size_t</span></code>. NuttX uses this <cite>flexible</cite> |
| definition of <code class="docutils literal notranslate"><span class="pre">size_t</span></code>:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="kt">size_t</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>It is <cite>flexible</cite> in the sense that <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> is determined by architecture |
| specific header files, <cite>not</cite> the RTOS itself. That definition will be either |
| <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">long</span></code> or <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">int</span></code>. So the <code class="docutils literal notranslate"><span class="pre">size_t</span></code> type compatibility |
| can differ with different compilers and also with different architectures |
| (NOTE that since <code class="docutils literal notranslate"><span class="pre">size_t</span></code> should be wide enough to hold the size of the |
| largest addressable object. <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> only works for 32-bit addressable |
| machines. Perhaps, <code class="docutils literal notranslate"><span class="pre">size_t</span></code> should really be defined as type <code class="docutils literal notranslate"><span class="pre">uintptr_t</span></code>?).</p> |
| <p>This can be fixed by changing the definition of <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> as described |
| above. But that could introduce <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> name mangling incompatibilities. |
| In that case, you have no option but to decouple the definition of <code class="docutils literal notranslate"><span class="pre">size_t</span></code> |
| from <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> by changing the definition in <code class="docutils literal notranslate"><span class="pre">nuttx/include/sys/types.h</span></code> |
| to:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="kt">size_t</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>or</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="kt">size_t</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>whichever resolves the incompatibility.</p> |
| </section> |
| </section> |
| </section> |
| |
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