From 57283ed7cbc6468ba36c2347935d84e4119d9430 Mon Sep 17 00:00:00 2001
From: patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3>
Date: Sat, 27 Jun 2009 00:56:39 +0000
Subject: [PATCH] Document binary loadr APIs
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1970 42af7a65-404d-4744-a932-0658087f49c3
---
Documentation/NuttXNxFlat.html | 199 ++++++++++++++++++++++++++++++---
TODO | 6 +-
2 files changed, 186 insertions(+), 19 deletions(-)
diff --git a/Documentation/NuttXNxFlat.html b/Documentation/NuttXNxFlat.html
index 289c8a35c1..6e92a4cf19 100644
--- a/Documentation/NuttXNxFlat.html
+++ b/Documentation/NuttXNxFlat.html
@@ -93,6 +93,12 @@
<a href="#making">1.4 Making an NXFLAT module</a>
</td>
</tr>
+<tr>
+ <td valign="top" width="22"><img height="20" width="20" src="favicon.ico"></td>
+ <td>
+ <a href="#binfmt">3.0. Binary Loader APIs</a>
+ </td>
+</tr>
<tr>
<td valign="top" width="22"><img height="20" width="20" src="favicon.ico"></td>
<td>
@@ -161,7 +167,7 @@
<p>
NXFLAT is derived from <a href="http://xflat.sourceforge.net/">XFLAT</a>.
XFLAT is a toolchain add that provides full shared library and XIP executable
- support for processors that have no Memory Management Unit (MMU).
+ support for processors that have no Memory Management Unit (MMU<sup>1</sup>).
NXFLAT is greatly simplified for the deeply embedded environment targeted by Nuttx:
</p>
<ul>
@@ -170,13 +176,19 @@
</ul>
<p>
Rather, the NXFLAT module only <i>imports</i> symbol values.
- In the NXFLAT model, the (PIC<sup>1</sup>) NXFLAT module resides in a FLASH file system and
+ In the NXFLAT model, the (PIC<sup>2</sup>) NXFLAT module resides in a FLASH file system and
when it is loaded at run time, it is dynamically linked only to the (non-PIC) base NuttX
code:
The base NuttX <i>exports</i> a symbol table; the NXFLAT module <i>imports</i> those symbol value
to dynamically bind the module to the base code.
</p>
-<p><sup>1</sup><small>"Position Independent Code"</small></p>
+
+<ul>
+ <p>
+ <sup>1</sup><small>MMU: "Memory Management Unit"</small><br>
+ <sup>2</sup><small>PIC: "Position Independent Code"</small>
+ </p>
+</ul>
<a name="limitations"><h2>1.3 Limitations</h2></a>
@@ -220,8 +232,8 @@
</ul>
<ul><p>
- <sup>1</sup><small>"Memory Management Unit"</small><br>
- <sup>2</sup><small>"Position Independent Code"</small><br>
+ <sup>1</sup><small>MMU: "Memory Management Unit"</small><br>
+ <sup>2</sup><small>PIC: "Position Independent Code"</small><br>
<sup>3</sup><small>A work around is under consideration:
At run time, the <code>.rodata</code> offsets will be indexed by a RAM address.
If the dynamic loader were to offset those <code>.rodata</code> offsets properly, it
@@ -406,27 +418,186 @@ any following arguments.
</table></ul>
<p><b>Target 1</b>.
- This target links all of the object files together into one relocation object.
- In this case, there is only a single object file, <code>hello.o</code>, and it is linked to produce <code>hello.r1</code>.
+ This target links all of the module's object files together into one relocatable object.
+ Two relocatable objects will be generated; this is the first one (hence, the suffic <code>.r1</code>).
+ In this "Hello, World!" case, there is only a single object file, <code>hello.o</code>,
+ that is linked to produce the <code>hello.r1</code> object.
+</p>
+
+<p>
+ When the module's object files are compiled, some special compiler CFLAGS must be provided.
+ First, the option <code>-fpic</code> is required to tell the compiler to generate position independent code (other
+ GCC options, like <code>-fno-jump-tables</code> might also be desirable).
+ For ARM compilers, two additional compilation options are required: <code>-msingle-pic-base</code>
+ and <code>-mpic-register=r10</code>.
</p>
<p><b>Target 2</b>.
- Given <code>hello.r1</code>, this target will invoke <a href="#mknxflat"><code>mknxflat</code></a>
+ Given the <code>hello.r1</code> relocatable object, this target will invoke
+ <a href="#mknxflat"><code>mknxflat</code></a>
to make the <i>thunk</i> file, <code>hello-thunk.S</code>.
- This <i>thunk</i> contains all of the information needed to create the imported function list.
+ This <i>thunk</i> file contains all of the information needed to create the imported function list.
</p>
<p><b>Target 3</b>
- This this target is similar to <b>Target 1</b>.
- In this case, it will link together the object file, <code>hello.o</code> along with the assembled <i>thunk</i> file,
- <code>hello-thunk.o</code> to create another, single relocatable object, <code>hello.r2</code>.
+ This target is similar to <b>Target 1</b>.
+ In this case, it will link together the module's object files (only <code>hello.o</code> here)
+ along with the assembled <i>thunk</i> file, <code>hello-thunk.o</code> to create the second relocatable object,
+ <code>hello.r2</code>.
The linker script, <code>gnu-nxflat.ld</code> is required at this point to correctly position the sections.
+ This linker script produces two segments:
+ An <i>I-Space</i> (Instruction Space) segment containing mostly <code>.text</code> and a <i>D-Space</i> (Data Space) segment
+ containing <code>.got</code>, <code>.data</code>, and <code>.bss</code> sections.
+ The I-Space section must be origined at address 0 (so that the segment's addresses are really offsets into
+ the I-Space segment)
+ and the D-Space section must also be origined at address 0 (so that segment's addresses are really offsets into
+ the I-Space segment).
+ The option <code>-no-check-sections</code> is required to prevent the linker from failing because these segments overlap.
</p>
<p><b>Target 4</b>.
Finally, this target will use the <code>hello.r2</code> relocatable object to create the final, NXFLAT module
- <code>hello</code> by calling <a href="#ldnxflat"><code>ldnxflat</code></a>.
+ <code>hello</code> by executing <a href="#ldnxflat"><code>ldnxflat</code></a>.
+</p>
+
+<table width ="100%">
+ <tr bgcolor="#e4e4e4">
+ <td>
+ <a name="binfmt"><h1>3.0 Binary Loader APIs</h1></a>
+ </td>
+ </tr>
+</table>
+
+<p><b>Relevant Header Files:</b></p>
+<ul>
+ <li>
+ The interface to the binary loader is described in the header file
+ <a href="http://nuttx.cvs.sourceforge.net/viewvc/nuttx/nuttx/include/nuttx/binfmt.h?revision=1.5&view=markup">
+ <code>include/nuttx/binfmt.h</code></a>.
+ A brief summary of the APIs prototyped in that header file are listed below.
+ </li>
+ <li>
+ NXFLAT APIs needed to register NXFLAT as a binary loader appear in the header file
+ <a href="http://nuttx.cvs.sourceforge.net/viewvc/*checkout*/nuttx/nuttx/include/nuttx/nxflat.h?revision=1.9">
+ <code>include/nuttx/nxflat.h</code></a>.
+ </li>
+ <li>
+ The format of an NXFLAT object itself is described in the header file:
+ <a href="http://nuttx.cvs.sourceforge.net/viewvc/*checkout*/nuttx/nuttx/include/nxflat.h?revision=1.12">
+ <code>include/nxflat.h</code></a>.
+ </li>
+</ul>
+
+<p><b>binfmt Registration</b>
+ These first interfaces are used only by a binary loader module, such as NXFLAT itself.
+ NXFLAT (or any future binary loader) calls <code>register_binfmt()</code> to incorporate
+ itself into the system.
+ In this way, the binary loader logic is dynamically extensible to support any kind of loader.
+ Normal application code should not be concerned with these interfaces.
+</p>
+
+<ul>
+<p><b><code>int register_binfmt(FAR struct binfmt_s *binfmt)</code></b>
+<ul>
+<p><b>Description:</b>
+ Register a loader for a binary format
+</p>
+<p><b>Returned Value:</b>
+ This is a NuttX internal function so it follows the convention that
+ 0 (<code>OK</code>) is returned on success and a negated errno is returned on
+ failure.
+</p>
+</ul>
+
+<p><b><code>int unregister_binfmt(FAR struct binfmt_s *binfmt)</code></b>
+<ul>
+<p><b>Description:</b>
+ Register a loader for a binary format
+</p>
+<p><b>Returned Value:</b>
+ This is a NuttX internal function so it follows the convention that
+ 0 (<code>OK</code>) is returned on success and a negated errno is returned on
+ failure.
+</p>
+</ul>
+</ul>
+
+<p><b>NXFLAT Initialization</b>
+ These interfaces are specific to NXFLAT.
+ Normally, an application needs only call <code>nxflat_initialize()</code> during its initialization
+ to have full NXFLAT support.
+</p>
+
+<ul>
+<p><b><code>int nxflat_initialize(void)</code></b>
+<ul>
+<p><b>Description:</b>
+ NXFLAT support is built unconditionally. However, it order to
+ use this binary format, this function must be called during system
+ format in order to register the NXFLAT binary format.
+ This function calls <code>register_binfmt()</code> appropriately.
</p>
+<p><b>Returned Value:</b>
+ This is a NuttX internal function so it follows the convention that
+ 0 (OK) is returned on success and a negated errno is returned on
+ failure.
+</p>
+</ul>
+
+<p><b><code>void nxflat_uninitialize(void)</code></b>
+<ul>
+<p><b>Description:</b>
+ Unregister the NXFLAT binary loader
+</p>
+<p><b>Returned Value:</b>
+ None
+</p>
+</ul>
+</ul>
+
+<p><b>Binary Loader Interfaces</b>.
+ The remaining APIs are called by user applications to maintain modules in the file system.
+</p>
+
+<ul>
+<p><b><code>int load_module(FAR struct binary_s *bin)</code></b>
+<ul>
+<p><b>Description:</b>
+ Load a module into memory, bind it to an exported symbol take, and
+ prep the module for execution.
+</p>
+<p><b>Returned Value:</b>
+ This is an end-user function, so it follows the normal convention:
+ Returns 0 (<code>OK</code>) on success. On failure, it returns -1 (<code>ERROR</code>) with
+ errno set appropriately.
+</p>
+</ul>
+
+<p><b><code>int unload_module(FAR const struct binary_s *bin)</code></b>
+<ul>
+<p><b>Description:</b>
+ Unload a (non-executing) module from memory. If the module has
+ been started (via <code>exec_module()</code>), calling this will be fatal.
+</p>
+<p><b>Returned Value:</b>
+ This is a NuttX internal function so it follows the convention that
+ 0 (<code>OK</code>) is returned on success and a negated errno is returned on
+ failure.
+</p>
+</ul>
+
+<p><b><code>int exec_module(FAR const struct binary_s *bin, int priority)</code></b>
+<ul>
+<p><b>Description:</b>
+ Execute a module that has been loaded into memory by load_module().
+</p>
+<p><b>Returned Value:</b>
+ This is an end-user function, so it follows the normal convention:
+ Returns the PID of the exec'ed module. On failure, it.returns
+ -1 (<code>ERROR</code>) and sets errno appropriately.
+</p>
+</ul>
+</ul>
<table width ="100%">
<tr bgcolor="#e4e4e4">
@@ -438,7 +609,7 @@ any following arguments.
<p>
When GCC generate position independent code, new code sections will appear in your programs.
- One of these the the GOT (Global Offset Table) and, in ELF environments, the PLT (Procedure
+ One of these is the GOT (Global Offset Table) and, in ELF environments, another is the PLT (Procedure
Lookup Table.
For example, if your C code generated (ARM) assembly language like this without PIC:
<p>
diff --git a/TODO b/TODO
index 3370e58c0c..90bc128479 100644
--- a/TODO
+++ b/TODO
@@ -13,7 +13,7 @@ NuttX TODO List (Last updated June 26, 2009)
(8) File system/Generic drivers (fs/, drivers/)
(2) Graphics subystem (graphics/)
(1) Pascal add-on (pcode/)
- (2) Documentation (Documentation/)
+ (1) Documentation (Documentation/)
(6) Build system / Toolchains
(3) NuttShell (NSH) (examples/nsh)
(3) Other Applications & Tests (examples/)
@@ -359,10 +359,6 @@ o Documentation (Documentation/)
Status: Open
Priority: Low
- Description: Need to document binary loader APIs
- Status: Open
- Priority: Low
-
o Build system
^^^^^^^^^^^^
--
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