Re: [edk2-devel] [PATCH] edk II C Coding Standard: Remove section 5.4.2.2 STATIC

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 22 Nov 2022 at 19:10, Michael D Kinney
<michael.d.kinney@intel.com> wrote:
>
> Hi Abner,
>
> Removing that section 5.4.2.2 is required to close this bug.
>
> Meaning of 'static' is covered by the ANSI C standards.
>
> Use of 'static' for non-public variable/functions in EDK II
> libraries/modules is recommended.
>
> However, it is not required.  It is recommended to reduce chances
> of symbol conflicts at link time.  Current approach is if a link
> failure occurs for multiply defined symbols and those are non-public
> symbols, the 'static' attribute can be applied to the non-public
> symbols in the components that generated the link failure.
>
> It may be good to mention this recommendation in the CSS.
>
> I will let you decide when this recommendation needs to be
> added to CSS.
>

'static' is not just a tool to avoid symbol conflicts. It also avoids
abuse of symbols that are assumed to have a private nature but can be
linked to nonetheless (e.g., in static libraries). Ideally, any
library should only export the symbols that it defines as part of its
interface, although this is not currently feasible of a library
consists of multiple object files.

Another thing to keep in mind is that static is used by the compiler
to make inferences about the value. A static global variable can only
be modified by the code in the same compilation unit, and so the
compiler is free to optimize accesses or perform constant propagation
and drop it entirely if it only observes reads and no writes from the
variable.

I consider it good developer hygiene to always use static on global
symbols (code and data) unless the symbol needs to be shared with
other compilation units.