optionally postpone assignment of Common

John Reiser jreiser@BitWagon.com
Tue Sep 25 21:13:00 GMT 2001

Hi Alan and binutils,

Using --no-define-common can save space, and can help prevent
selecting an impostor when many dynamic modules have special
search rules for symbol resolution.

Index: ld.texinfo
RCS file: /cvs/src/src/ld/ld.texinfo,v
retrieving revision 1.51
diff -u -r1.51 ld.texinfo
--- ld.texinfo	2001/09/24 18:35:08	1.51
+++ ld.texinfo	2001/09/26 03:59:04
@@ -950,6 +950,24 @@
 symbol is defined, the first file listed is the location of the
 definition.  The remaining files contain references to the symbol.
+@cindex common allocation
+@kindex --no-define-common
+@item --no-define-common
+This option inhibits the assignment of addresses to common symbols.
+The script command @code{INHIBIT_COMMON_ALLOCATION} has the same effect.
+@xref{Miscellaneous Commands}.
+The @samp{--no-define-common} option allows decoupling
+the decision to assign addresses to Common symbols from the choice
+of the output file type; otherwise a non-Relocatable output type
+forces assigning addresses to Common symbols.
+Using @samp{--no-define-common} allows Common symbols that are referenced
+from a shared library to be assigned addresses only in the main program.
+This eliminates the unused duplicate space in the shared library,
+and also prevents any possible confusion over resolving to the wrong
+duplicate when there are many dynamic modules with specialized search
+paths for runtime symbol resolution.
 @cindex symbols, from command line
 @kindex --defsym @var{symbol}=@var{exp}
 @item --defsym @var{symbol}=@var{expression}
@@ -2310,6 +2328,13 @@
 This command has the same effect as the @samp{-d} command-line option:
 to make @code{ld} assign space to common symbols even if a relocatable
 output file is specified (@samp{-r}).
+@cindex common allocation in linker script
+This command has the same effect as the @samp{--no-define-common}
+command-line option: to make @code{ld} omit the assignment of addresses
+to common symbols even for a non-relocatable output file.
 @item NOCROSSREFS(@var{section} @var{section} @dots{})
 @kindex NOCROSSREFS(@var{sections})

John Reiser, jreiser@BitWagon.com

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