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Introducing the "linker_weak" linkage type. This will be used for Objective-C

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metadata types which should be marked as "weak", but which the linker will
remove upon final linkage. For example, the "objc_msgSend_fixup_alloc" symbol is
defined like this:

       .globl l_objc_msgSend_fixup_alloc
       .weak_definition l_objc_msgSend_fixup_alloc
       .section __DATA, __objc_msgrefs, coalesced
       .align 3
l_objc_msgSend_fixup_alloc:
        .quad   _objc_msgSend_fixup
        .quad   L_OBJC_METH_VAR_NAME_1

This is different from the "linker_private" linkage type, because it can't have
the metadata defined with ".weak_definition".


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107205 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling
2010-06-29 21:24:00 +00:00
parent 147b7cad2f
commit 207855cff9
26 changed files with 94 additions and 39 deletions
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31
docs/LangRef.html
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@@ -24,6 +24,7 @@
<ol>
<li><a href="#linkage_private">'<tt>private</tt>' Linkage</a></li>
<li><a href="#linkage_linker_private">'<tt>linker_private</tt>' Linkage</a></li>
<li><a href="#linkage_linker_weak">'<tt>linker_weak</tt>' Linkage</a></li>
<li><a href="#linkage_internal">'<tt>internal</tt>' Linkage</a></li>
<li><a href="#linkage_available_externally">'<tt>available_externally</tt>' Linkage</a></li>
<li><a href="#linkage_linkonce">'<tt>linkonce</tt>' Linkage</a></li>
@@ -546,23 +547,27 @@ define i32 @main() { <i>; i32()* </i>
<dl>
<dt><tt><b><a name="linkage_private">private</a></b></tt></dt>
<dd>Global values with private linkage are only directly accessible by objects
in the current module. In particular, linking code into a module with an
private global value may cause the private to be renamed as necessary to
avoid collisions. Because the symbol is private to the module, all
references can be updated. This doesn't show up in any symbol table in the
object file.</dd>
<dd>Global values with "<tt>private</tt>" linkage are only directly accessible
by objects in the current module. In particular, linking code into a
module with an private global value may cause the private to be renamed as
necessary to avoid collisions. Because the symbol is private to the
module, all references can be updated. This doesn't show up in any symbol
table in the object file.</dd>
<dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt>
<dd>Similar to private, but the symbol is passed through the assembler and
removed by the linker after evaluation. Note that (unlike private
symbols) linker_private symbols are subject to coalescing by the linker:
weak symbols get merged and redefinitions are rejected. However, unlike
normal strong symbols, they are removed by the linker from the final
linked image (executable or dynamic library).</dd>
<dd>Similar to <tt>private</tt>, but the symbol is passed through the
assembler and removed by the linker after evaluation. Note that (unlike
<tt>private</tt> symbols) <tt>linker_private</tt> symbols are subject to
coalescing by the linker: weak symbols get merged and redefinitions are
rejected. However, unlike normal strong symbols, they are removed by the
linker from the final linked image (executable or dynamic library).</dd>
<dt><tt><b><a name="linkage_linker_weak">linker_weak</a></b></tt></dt>
<dd>Global values with "<tt>linker_weak</tt>" linkage are given weak linkage,
but are removed by the linker after evaluation.</dd>
<dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt>
<dd>Similar to private, but the value shows as a local symbol
<dd>Similar to <tt>private</tt>, but the value shows as a local symbol
(<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This
corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd>