Messages in this thread | | | From | Segher Boessenkool <> | Subject | Re: kernel + gcc 4.1 = several problems | Date | Thu, 4 Jan 2007 17:43:36 +0100 |
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> Adjusting gcc flags to eliminate optimizations is another way to go. > Adding -fwrapv would be an excellent start. Lack of this flag breaks > most code which checks for integer wrap-around.
Lack of the flag does not break any valid C code, only code making unwarranted assumptions (i.e., buggy code).
> The compiler "knows" > that signed integers don't ever wrap, and thus eliminates any code > which checks for values going negative after a wrap-around.
You cannot assume it eliminates such code; the compiler is free to do whatever it wants in such a case.
You should typically write such a computation using unsigned types, FWIW.
Anyway, with 4.1 you shouldn't see frequent problems due to "not using -fwrapv while my code is broken WRT signed overflow" yet; and if/when problems start to happen, to "correct" action to take is not to add the compiler flag, but to fix the code.
Segher
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