Messages in this thread | | | Subject | Re: [PATCH v2] statx: optimize copy of struct statx to userspace | From | Florian Weimer <> | Date | Mon, 13 Mar 2017 11:27:32 +0100 |
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On 03/13/2017 05:34 AM, Andreas Dilger wrote: > Not that it is a huge deal either way, but I'd think it is harder for the > compiler to optimize across a function call boundary like memset() vs. a > struct initialization in the same function where it can see that all but > a few of the fields are being overwritten immediately before they are used.
GCC treats memset as a function call only if options such as -ffreestanding or -fno-builtin are enabled, or if memset is redefined in a header file. Does the kernel do this?
> I don't think the designated initializer is any less clear to the reader > that the struct is zeroed out compared to using memset(). Possibly the > best compromise is to use a designated initializer that specifies all of > the known fields, and leaves it to the compiler to initialize unset fields > or padding.
GCC will not always initialize padding if you specify a designated initializer because padding values are unspeficied and their value does not matter from a language point of view.
Thanks, Florian
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