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On Wed, 17 Feb 2010, Grant Likely wrote:
Question. If I use this pattern, and use the __weak attribute on core
code functions wrapped with a #ifndef, then how does it mesh with
EXPORT_SYMBOL*() statements?
You cant. Or at least not the traditional way, which is to put the
EXPORT_SYMBOL next to the definition of what gets exported.
If you use __weak, you need to make sure that all users of said weak
symbol are in another file. There are some compiler and/or binutils bugs
with using weak symbols in the same translation unit, so the rule is that
a weak definition hes to be somewhere else from the use - including
EXPORT_SYMBOL.
I also assume that at the core code site, the EXPORT_SYMBOL() must
appear inside the #ifndef block so that a #define override doesnt
break things. Correct?
See above. You cant put it inside the _same_ #ifndef block. Youd have to
put it in a different file, but yes, inside an ifndef. At which point the
linker will just pick the right definition.
However, in general, this probably gets ugly enough that the whole __weak
thing is not great for exported stuff. Its likely mostly useful for some
"generic" arch functionality that is always compiled in.
Linus
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