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
