Quoting Kees Cook (2019-02-20 14:26:06)

On Fri, Feb 15, 2019 at 4:34 PM Stephen Boyd [off-list ref] wrote:

quoted

Quoting Kees Cook (2019-02-12 10:57:05)

quoted

On Mon, Feb 11, 2019 at 11:41 PM Krzysztof Kozlowski [off-list ref] wrote:

quoted

It is just the GCC which has to be fixed not the code. You want to
adjust the code for specific version of GCC and what if GCC changes
its warning? For example GCC might require "fall through: "... or any
other syntax. Another point - what about clang's syntax?

-Wimplicit-fallthrough=3 is stricter and maps to -Wextra, hence its
choice. GCC's levels were chosen based on the existing linters, static
analyzers, etc. The patterns are unlikely to change (see the gcc
man-page).

Clang doesn't recognize anything in C mode (hopefully this will be
fixed in the future[1]).

As long as one of the compilers is able to check this, we'll avoid the
bugs associated with this mis-pattern. Gustavo's efforts here have
found kind of a lot of bugs, so I think it's worth a little churn to
add these (and make minor adjustments to existing comments).

Just curious, what compilation phase does this check run in? Could we
gain a macro like FALLTHRU or even lowercase 'fallthru' that expanded to
whatever the compiler wants to see and then there would only be "one
way" to do this?  It would alleviate the above concerns, but maybe I'm
rehashing something that's already been proposed and rejected.

When this got discussed a while back, the thinking was that since
we're also dealing with static analyzers (e.g. Coverity) and IDEs that
literally parse comments in the code, it was most sensible (at least
for now, prior to there being a formal C "fall through" statement --
there is for C++ but not yet for C), we'd stick to explicit comments.
In theory, we will be able to do a tree-wide change to add the C
statement once it exists.

Ok, thanks for the background. Looks like the perf tool already
introduced the #define __fallthrough that they use for this purpose.
Maybe they're hoping that it will be formalized.


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