diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst index 49e0f64a3427deeec7eebf456e2549085ab378ff..053b24a6dd38cce19fc6d5ae1ed800dcb55cab00 100644 --- a/Documentation/process/deprecated.rst +++ b/Documentation/process/deprecated.rst @@ -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 +`_, 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. diff --git a/Makefile b/Makefile index 9be5834073f8937f5ceb358e620af0795243b56d..bdf8eac51b079f0e4cee09e6d7cda1110e43144b 100644 --- a/Makefile +++ b/Makefile @@ -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