SD wrote: > Hello, > > After searching this list it appears that with recent gcc (I am using gcc > 4.1), C++ exception handling has zero overhead (unless an exception actually > happens) > > Where can I find more information on how exception handling is done and if > this zero overhead property is always true.
There are two EH mechanisms in gcc, one using a Dwarf-2 table-driven implementation, the other based around use of setjmp-longjmp. Which one is used depends on the --en/disable-sjlj-exceptions flag at configure time. The DW2 version has zero overhead in terms of execution time when no exceptions are thrown, but adds a noticeable amount of memory usage for the eh tables. The sjlj version incurs a time penalty every time it enters an EH region, and probably incurs more stack usage doing so, but doesn't have all the big static data tables that DW2 has. > I looked a a couple of manuals on the gcc homepage but could not find > anything. Don't think there's much about sjlj except in the gcc sources themselves. There's a page about DW2 EH on the wiki: http://gcc.gnu.org/wiki/Dwarf2EHNewbiesHowto cheers, DaveK
