mirror of
https://github.com/rn10950/RetroZilla.git
synced 2024-11-14 03:30:17 +01:00
213 lines
8.9 KiB
HTML
213 lines
8.9 KiB
HTML
<html>
|
|
<head>
|
|
<title>xptcall Porting Guide</title>
|
|
</head>
|
|
<body bgcolor = "white">
|
|
<h2><center>xptcall Porting Guide</center></h2>
|
|
|
|
<h3>Overview</h3>
|
|
|
|
<blockquote>
|
|
|
|
<a href="http://www.mozilla.org/scriptable/xptcall-faq.html"> xptcall</a> is a
|
|
library that supports both invoking methods on arbitrary xpcom objects and
|
|
implementing classes whose objects can impersonate any xpcom interface. It does
|
|
this using platform specific assembly language code. This code needs to be
|
|
ported to all platforms that want to support xptcall (and thus mozilla).
|
|
|
|
</blockquote>
|
|
|
|
<h3>The tree</h3>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall">mozilla/xpcom/reflect/xptcall</a>
|
|
+--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public">public</a> // exported headers
|
|
+--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src">src</a> // core source
|
|
| \--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md">md</a> // platform specific parts
|
|
| +--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/mac">mac</a> // mac ppc
|
|
| +--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/unix">unix</a> // all unix
|
|
| \--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/win32">win32</a> // win32
|
|
| +--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/test">test</a> // simple tests to get started
|
|
\--<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/tests">tests</a> // full tests via api
|
|
</pre>
|
|
|
|
Porters are free to create subdirectories under the base <code>md</code>
|
|
directory for their given platforms and to integrate into the build system as
|
|
appropriate for their platform.
|
|
|
|
</blockquote>
|
|
|
|
<h3>Theory of operation</h3>
|
|
|
|
<blockquote>
|
|
|
|
There are really two pieces of functionality: <i>invoke</i> and <i>stubs</i>...
|
|
|
|
<p>
|
|
|
|
The <b><i>invoke</i></b> functionality requires the implementation of the
|
|
following on each platform (from <a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public/xptcall.h#131">xptcall/public/xptcall.h</a>):
|
|
|
|
<pre>
|
|
XPTC_PUBLIC_API(nsresult)
|
|
XPTC_InvokeByIndex(nsISupports* that, PRUint32 methodIndex,
|
|
PRUint32 paramCount, nsXPTCVariant* params);
|
|
</pre>
|
|
|
|
Calling code is expected to supply an array of <code>nsXPTCVariant</code>
|
|
structs. These are discriminated unions describing the type and value of each
|
|
parameter of the target function. The platform specific code then builds a call
|
|
frame and invokes the method indicated by the index <code>methodIndex</code> on
|
|
the xpcom interface <code>that</code>.
|
|
|
|
<p>
|
|
|
|
Here are examples of this implementation for
|
|
<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/win32/xptcinvoke.cpp">Win32</a>
|
|
and
|
|
<a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/unix/xptcinvoke_unixish_x86.cpp">Linux x86, NetBSD x86, and FreeBSD</a>.
|
|
|
|
Both of these implementations use the basic strategy of: figure out how much
|
|
stack space is needed for the params, make the space in a new frame, copy the
|
|
params to that space, invoke the method, cleanup and return. C++ is used where
|
|
appropriate, Assembly language is used where necessary. Inline assembly language is used here,
|
|
but it is equally valid to use separate assembly language source files. Porters
|
|
can decide how best to do this for their platforms.
|
|
|
|
<p>
|
|
|
|
The <b><i>stubs</i></b> functionality is more complex. The goal here is a class
|
|
whose vtbl can look like the vtbl of any arbitrary xpcom interface. Objects of
|
|
this class can then be built to impersonate any xpcom object. The base interface
|
|
for this is (from <a href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public/xptcall.h#109">xptcall/public/xptcall.h</a>):
|
|
|
|
<pre>
|
|
class nsXPTCStubBase : public nsISupports
|
|
{
|
|
public:
|
|
// Include generated vtbl stub declarations.
|
|
// These are virtual and *also* implemented by this class..
|
|
#include "xptcstubsdecl.inc"
|
|
|
|
// The following methods must be provided by inheritor of this class.
|
|
|
|
// return a refcounted pointer to the InterfaceInfo for this object
|
|
// NOTE: on some platforms this MUST not fail or we crash!
|
|
NS_IMETHOD GetInterfaceInfo(nsIInterfaceInfo** info) = 0;
|
|
|
|
// call this method and return result
|
|
NS_IMETHOD CallMethod(PRUint16 methodIndex,
|
|
const nsXPTMethodInfo* info,
|
|
nsXPTCMiniVariant* params) = 0;
|
|
};
|
|
</pre>
|
|
|
|
Code that wishes to make use of this <i>stubs</i> functionality (such as
|
|
<a href="http://www.mozilla.org/scriptable/">XPConnect</a>) implement a class
|
|
which inherits from <code>nsXPTCStubBase</code> and implements the
|
|
<code>GetInterfaceInfo</code> and <code>CallMethod</code> to let the
|
|
platform specific code know how to get interface information and how to dispatch methods
|
|
once their parameters have been pulled out of the platform specific calling
|
|
frame.
|
|
|
|
<p>
|
|
|
|
Porters of this functionality implement the platform specific code for the
|
|
<i>stub</i> methods that fill the vtbl for this class. The idea here is that the
|
|
class has a vtbl full of a large number of generic stubs. All instances of this
|
|
class share that vtbl and the same stubs. The stubs forward calls to a platform
|
|
specific method that uses the interface information supplied by
|
|
the overridden <code>GetInterfaceInfo</code> to extract the parameters and build
|
|
an array of platform independent <code>nsXPTCMiniVariant</code> structs which
|
|
are in turn passed on to the overridden <code>CallMethod</code>. The
|
|
platform dependent code is responsible for doing any cleanup and returning.
|
|
|
|
<p>
|
|
|
|
The stub methods are declared in <a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public/xptcstubsdecl.inc">xptcall/public/xptcstubsdecl.inc</a>.
|
|
These are '#included' into the declaration of <code>nsXPTCStubBase</code>. A
|
|
similar include file (<a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public/xptcstubsdef.inc">xptcall/public/xptcstubsdef.inc</a>)
|
|
is expanded using platform specific macros to define the stub functions. These
|
|
'.inc' files are checked into cvs. However, they can be regenerated as necessary
|
|
(i.e. to change the number of stubs or to change their specific declaration)
|
|
using the Perl script <a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/public/genstubs.pl">xptcall/public/genstubs.pl</a>.
|
|
|
|
<p>
|
|
|
|
Here are examples of this implementation for <a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/win32/xptcstubs.cpp">Win32</a>
|
|
and <a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/unix/xptcstubs_unixish_x86.cpp">Linux x86, NetBSD x86, and FreeBSD</a>.
|
|
Both of these examples use inline assembly language. That is just how I
|
|
decided to do it. You can do it as you choose.
|
|
|
|
<p>
|
|
|
|
The Win32 version is somewhat tighter because the __declspec(naked) feature
|
|
allows for very small stubs. However, the __stdcall requires the callee to clean
|
|
up the stack, so it is imperative that the interface information scheme allow
|
|
the code to determine the correct stack pointer fixup for return without fail,
|
|
else the process will crash.
|
|
|
|
<p>
|
|
|
|
I opted to use inline assembler for the gcc Linux x86 port. I ended up with
|
|
larger stubs than I would have preferred rather than battle the compiler over
|
|
what would happen to the stack before my asm code began running.
|
|
|
|
<p>
|
|
|
|
I believe that the non-assembly parts of these files can be copied and reused
|
|
with minimal (but not zero) platform specific tweaks. Feel free to copy and
|
|
paste as necessary. Please remember that safety and reliability are more
|
|
important than speed optimizations. This code is primarily used to connect XPCOM
|
|
components with JavaScript; function call overhead is a <b>tiny</b> part of the
|
|
time involved.
|
|
|
|
<p>
|
|
|
|
I put together
|
|
<a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/src/md/test">xptcall/src/md/test
|
|
</a> as a place to evolve the basic functionality as a port is coming together.
|
|
Not all of the functionality is exercised, but it is a place to get started.
|
|
<a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/tests">xptcall/tests
|
|
</a> has an api level test for <code>XPTC_InvokeByIndex</code>, but no tests for
|
|
the <i>stubs</i> functionality. Such a test ought to be written, but this has not
|
|
yet been done.
|
|
|
|
<p>
|
|
|
|
A full 'test' at this point requires building the client and running the
|
|
XPConnect test called <i>TestXPC</i> in
|
|
<a
|
|
href="http://lxr.mozilla.org/mozilla/source/js/src/xpconnect/tests">mozilla/js/src/xpconnect/tests
|
|
</a>.
|
|
|
|
<p>
|
|
|
|
Getting these ports done is very important. Please let <a
|
|
href="mailto:jband@netscape.com">me</a> know if you are interested in doing one.
|
|
I'll answer any questions as I get them.
|
|
|
|
<p>
|
|
|
|
<a
|
|
href="http://lxr.mozilla.org/mozilla/source/xpcom/reflect/xptcall/status.html">
|
|
Porting Status
|
|
</a>
|
|
|
|
</blockquote>
|
|
|
|
<hr>
|
|
<b>Author:</b> <a href="mailto:jband@netscape.com">John Bandhauer <jband@netscape.com></a><br>
|
|
<b>Last modified:</b> 31 May 1999
|
|
|
|
</body>
|
|
</html>
|