Re: [git patches 1/2] warnings: attack valid cases spotted by warnings
From: Jeff Garzik
Date: Tue Jul 17 2007 - 23:30:22 EST
Roland Dreier wrote:
In this case the code is basically
u32 x;
for (n = 0; cond; ++n) {
...
if (!n)
x = something;
...
}
if (n) {
...
use(x);
...
}
and gcc still warns...
Interestingly, the above accurately describes a common code pattern
matching code which caused gcc to emit the uninit'd-var warnings.
For the record I think initializating 'f0' to zero is safer for the
reasons Linus gave, and in addition, f0 is or'd with a value written to
a hardware register, which means things should go awry (if they go) in a
semi-predictable manner.
According to the assembly language produced, sure it is larger -- by one
(per function) MOV that is adjacent to other initializations, making it
highly likely the initializations are all streamed together. I doubt
one MOV per function will make a huge difference, considering the peace
of mind it buys.
Jeff
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