Messages in this thread | | | Date | Tue, 11 Feb 2003 11:24:38 +0100 | From | Helge Hafting <> | Subject | Re: Is -fno-strict-aliasing still needed? |
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Horst von Brand wrote: > > Art Haas <ahaas@airmail.net> said: > > I ask because I've just built a kernel without using that flag - > > linus-2.5 BK from this morning, probably missing the 2.5.60 release by > > a few hours. > > The problem with strict aliasing is that it allows the compiler to assume > that in: > > void somefunc(int *foo, int *bar) > > foo and bar will _*never*_ point to the same memory area (at the same > struct, or into the same array, etc). There is no way to check for this in > the compiler in general (the function and the call might be in different > files, many functions are being called via pointers, ...).
I though pointers to the same type, such as int *, could alias still.
But pointers to different types, such as int* and short* is assumed to never clash with strict aliasing. And this bites linux because it sometimes choose to see "two adjacent shorts as one int" for performance reasons.
I remember the flag was introduced because some IP or TCP code do exactly this, and converting it all to unions would render that code unreadable.
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