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Makefile: Globally enable fall-through warning

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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: Gustavo A. R. Silva <gustavo@embeddedor.com>
This commit is contained in:
Gustavo A. R. Silva 2019-06-06 19:46:17 -05:00
parent 2defb94edb
commit a035d552a9
2 changed files with 17 additions and 0 deletions
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14
Documentation/process/deprecated.rst
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@ -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.

3
Makefile
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@ -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