http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55693
--- Comment #41 from Jack Howarth <howarth at nitro dot med.uc.edu> 2013-01-24
15:23:54 UTC ---
Iain,
I believe the current behavior of dyld in darwin10/11/12 is clearly
described in...
http://developer.apple.com/library/mac/#releasenotes/DeveloperTools/RN-dyld/_index.html
Specifically in the section...
Faster Weak-symbol Coalescing
C++ uses weak definitions to solve a number of issues. But if weak symbols are
not hidden, the dynamic loader needs to make them unique at runtime. The
previous algorithm for doing that was expensive. For every weak symbol in each
image, the dynamic loader would look up that symbol in every other image. In OS
X v10.6 the algorithm is more efficient: It assumes that weak-symbol duplicates
are rare. First, all symbols are bound by their normal two-level namespace
binding. Then there is as a separate pass that takes an alphabetized list of
weak symbols from each image and iterates through just those weak symbols
looking for duplicates. The dynamic loader updates only the duplicates. The new
LINKEDIT segment format is optimized for this algorithm.
This issue seems to also be described in this thread on cfe-commits...
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059752.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059755.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059793.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059796.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059799.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059803.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059807.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059819.html
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120625/059825.html
