Commit a035d552 authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva
Browse files

Makefile: Globally enable fall-through warning 



Now that all the fall-through warnings have been addressed in the
kernel, enable the fall-through warning globally.

Also, update the deprecated.rst file to include implicit fall-through
as 'deprecated' so people can be pointed to a single location for
justification.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: default avatarGustavo A. R. Silva <gustavo@embeddedor.com>
parent 2defb94e

Documentation/process/deprecated.rst

+14 −0
Original line number Diff line number Diff line
@@ -119,3 +119,17 @@ array may exceed the remaining memory in the stack segment. This could 
lead to a crash, possible overwriting sensitive contents at the end of the

stack (when built without `CONFIG_THREAD_INFO_IN_TASK=y`), or overwriting

memory adjacent to the stack (when built without `CONFIG_VMAP_STACK=y`)



Implicit switch case fall-through

---------------------------------

The C language allows switch cases to "fall through" when

a "break" statement is missing at the end of a case. This,

however, introduces ambiguity in the code, as it's not always

clear if the missing break is intentional or a bug. As there

have been a long list of flaws `due to missing "break" statements

<https://cwe.mitre.org/data/definitions/484.html>`_, we no longer allow

"implicit fall-through". In order to identify an intentional fall-through

case, we have adopted the marking used by static analyzers: a comment

saying `/* Fall through */`. Once the C++17 `__attribute__((fallthrough))`

is more widely handled by C compilers, static analyzers, and IDEs, we can

switch to using that instead.

Makefile

+3 −0
Original line number Diff line number Diff line
@@ -843,6 +843,9 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) 
# warn about C99 declaration after statement

KBUILD_CFLAGS += -Wdeclaration-after-statement



# Warn about unmarked fall-throughs in switch statement.

KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=3,)



# Variable Length Arrays (VLAs) should not be used anywhere in the kernel

KBUILD_CFLAGS += -Wvla

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