On Mon, Feb 12, 2024 at 12:57:02PM -0800, Dan Williams wrote: > Lukas Wunner wrote: > > On Mon, Feb 12, 2024 at 11:07:06AM -0800, Dan Williams wrote: > > > Lukas Wunner wrote: > > > > In x509_cert_parse(), add a hint for the compiler that kzalloc() > > > > never returns an ERR_PTR(). Otherwise the compiler adds a gratuitous > > > > IS_ERR() check on return. Introduce a handy assume() macro for this > > > > which can be re-used elsewhere in the kernel to provide hints for the > > > > compiler. > > Might I suggest the following: > > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > index bb1339c..384803e 100644 > > --- a/include/linux/compiler.h > > +++ b/include/linux/compiler.h > > @@ -139,6 +139,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > > } while (0) > > #endif > > > > +#define assume(cond) do if(!(cond)) __builtin_unreachable(); while(0) > > s/__builtin_unreachable()/unreachable()/? I tried that and it didn't work. The superfluous IS_ERR() check was not optimized away by gcc. It seemed to remove the unreachable portion of the code before using it for optimization of the code. > Move this to cleanup.h and add extend the DEFINE_FREE() comment about > its usage: Yes, spreading the knowledge in this way might make sense. I'll wait for Peter to weigh in before submitting that though. Thanks, Lukas
