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authorBill Wendling <isanbard@gmail.com>2012-02-16 01:10:50 +0000
committerBill Wendling <isanbard@gmail.com>2012-02-16 01:10:50 +0000
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Give a description of the Objective-C garbage collection module flags.
The rule governing the flags is this: no-gc + no-gc = no-gc no-gc + gc = no-gc no-gc + gc-only = error gc + gc = gc gc + gc-only = gc-only gc-only + gc-only = gc-only git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150646 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
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1 files changed, 73 insertions, 0 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html
index 074e91e..5d3c745 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -110,6 +110,7 @@
</li>
<li><a href="#module_flags">Module Flags Metadata</a>
<ol>
+ <li><a href="#objc_gc_flags">Objective-C Garbage Collection Module Flags Metadata</a></li>
</ol>
</li>
<li><a href="#intrinsic_globals">Intrinsic Global Variables</a>
@@ -3147,12 +3148,84 @@ call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
<pre class="doc_code">
metadata !{ metadata !"foo", i32 1 }
</pre>
+
<p>The behavior is to emit an error if the <tt>llvm.module.flags</tt> does
not contain a flag with the ID <tt>!"foo"</tt> that has the value
'1'. If two or more <tt>!"qux"</tt> flags exist, then they must have
the same value or an error will be issued.</p></li>
</ul>
+
+<!-- ======================================================================= -->
+<h3>
+<a name="objc_gc_flags">Objective-C Garbage Collection Module Flags Metadata</a>
+</h3>
+
+<div>
+
+<p>On the Mach-O platform, Objective-C stores metadata about garbage collection
+ in a special section called "image info". The metadata consists of a version
+ number and a bitmask specifying what types of garbage collection are
+ supported (if any) by the file. If two or more modules are linked together
+ their garbage collection metadata needs to be merged rather than appended
+ together.</p>
+
+<p>The Objective-C garbage collection module flags metadata consists of the
+ following key-value pairs:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <th width="30%">Key</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td><tt>Objective-C&nbsp;Version</tt></td>
+ <td align="left"><b>[Required]</b> &mdash; The Objective-C ABI
+ version. Valid values are 1 and 2.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C&nbsp;Image&nbsp;Info&nbsp;Version</tt></td>
+ <td align="left"><b>[Required]</b> &mdash; The version of the image info
+ section. Currently always 0.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C&nbsp;Image&nbsp;Info&nbsp;Section</tt></td>
+ <td align="left"><b>[Required]</b> &mdash; The section to place the
+ metadata. Valid values are <tt>"__OBJC, __image_info, regular"</tt> for
+ Objective-C ABI version 1, and <tt>"__DATA,__objc_imageinfo, regular,
+ no_dead_strip"</tt> for Objective-C ABI version 2.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C&nbsp;Garbage&nbsp;Collection</tt></td>
+ <td align="left"><b>[Required]</b> &mdash; Specifies whether garbage
+ collection is supported or not. Valid values are 0, for no garbage
+ collection, and 2, for garbage collection supported.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C&nbsp;GC&nbsp;Only</tt></td>
+ <td align="left"><b>[Optional]</b> &mdash; Specifies that only garbage
+ collection is supported. If present, its value must be 6. This flag
+ requires that the <tt>Objective-C Garbage Collection</tt> flag have the
+ value 2.</td>
+ </tr>
+ </tbody>
+</table>
+
+<p>Some important flag interactions:</p>
+
+<ul>
+ <li>If a module with <tt>Objective-C Garbage Collection</tt> set to 0 is
+ merged with a module with <tt>Objective-C Garbage Collection</tt> set to
+ 2, then the resulting module has the <tt>Objective-C Garbage
+ Collection</tt> flag set to 0.</li>
+
+ <li>A module with <tt>Objective-C Garbage Collection</tt> set to 0 cannot be
+ merged with a module with <tt>Objective-C GC Only</tt> set to 6.</li>
+</ul>
+
+</div>
+
</div>
<!-- *********************************************************************** -->