http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46770
--- Comment #15 from H.J. Lu <hjl.tools at gmail dot com> 2010-12-11 18:46:48 UTC --- (In reply to comment #14) > H.J. -- > > Some of the statements that you're making in Comment #11 are inaccurate or > unclear: > > Given: > > Foo foo(...); > Bar bar(...); > > within a single module, the C++ standard guarantees that foo is initialized > before bar. See \S 3.6.2 "Initialization of non-local objects": > > "Other objects defined in namespace scope have ordered initialization. Objects > defined within a single translation unit and with ordered initialization shall > be initialized in the order of their definitions in the translation unit." > > Now, it is true that if foo or bar is zero-initialized or constant-initialized > (these are terms of art in the C++ standard) that initialization happens > before > dynamic initialization, so given: > > Foo foo(...); > int i = 3; > > It is guaranteed that "i" is initialized before "foo". But, even in that > case, > the order is well-defined; it's just not necessarily the order in which the > objects are declared. Thanks for correction/clarification. > Although the C++ standard does not impose requirements on initialization order > across translation units (i.e., source files), there is no doubt that programs > accidentally or intentionally depend upon it. I'm sure that making changes in > this regard will break something. But, such breakage is akin to the breakage > that occurs whenever we optimize more aggressively; people depend on current > undocumented behaviors, and programs break when we make a change. So, I don't > think we should resist making the change to .init_array simply on this ground. That is very true, specially for LTO. > On the other hand, we do have an issue around constructor priorities. If I > recall correctly, the linker sorts all of the .ctors.NNNNN sections into a > single array which is then executed in order. So, if the program has some > object files built using .ctors.NNNNN and others using .init_array, I don't > see > how we can get the interleaving that is specified in the source code. Linker supports sorting .ctors.NNNNN and .init_array.NNNN. Within .ctors.NNNNN and .init_array.NNNN, the order is defined. And ctors.NNNNN will be called before .init_array.NNNN. If you have constructor priorities in .o files and .c files, you may get different behaviors if .o files are compiled with a different compiler, different versions of GCC or not GCC at all.
