http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48127
--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> 2011-03-16 09:40:35 UTC --- On Tue, 15 Mar 2011, d.g.gorbachev at gmail dot com wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48127 > > --- Comment #3 from Dmitry Gorbachev <d.g.gorbachev at gmail dot com> > 2011-03-15 18:00:23 UTC --- > I do not agree that the testcase is invalid. As the standart says: > > Common extensions > > Multiple external definitions > > There may be more than one external definition for the identifier of > an object, with or without the explicit use of the keyword extern; if > the definitions disagree, or more than one is initialized, the behavior > is undefined. > > According to the Binutils documentation, > > The linker turns a common symbol into a declaration, if there is a > definition of the same variable. > > Also, from Ian Lance Taylor's article [1]: > > 5. If A is a strong definition in an object file: > > * If B is a common symbol, then we treat B as an undefined reference. > > I think it would be better to fix this problem in the linker. Gold does not > even warn about it! > > However, I don't understand why GCC makes baz[8] to have 32 bytes alignment, > while baz[4] has only 4 bytes alignment. It seems to be a GCC bug. It's an optimization to ensure accesses larger than 4 do not cross cacheline boundaries. Richard.
