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-rw-r--r-- | Documentation/process/deprecated.rst | 48 |
1 files changed, 29 insertions, 19 deletions
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst index 7160a449e6c6..8965446f0b71 100644 --- a/Documentation/process/deprecated.rst +++ b/Documentation/process/deprecated.rst @@ -94,8 +94,8 @@ and other misbehavior due to the missing termination. It also NUL-pads the destination buffer if the source contents are shorter than the destination buffer size, which may be a needless performance penalty for callers using only NUL-terminated strings. The safe replacement is :c:func:`strscpy`. -(Users of :c:func:`strscpy` still needing NUL-padding will need an -explicit :c:func:`memset` added.) +(Users of :c:func:`strscpy` still needing NUL-padding should instead +use strscpy_pad().) If a caller is using non-NUL-terminated strings, :c:func:`strncpy()` can still be used, but destinations should be marked with the `__nonstring @@ -144,27 +144,37 @@ 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. +The C language allows switch cases to fall through to the next case +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. For example, it's not obvious just from +looking at the code if `STATE_ONE` is intentionally designed to fall +through into `STATE_TWO`:: + + switch (value) { + case STATE_ONE: + do_something(); + case STATE_TWO: + do_other(); + break; + default: + WARN("unknown state"); + } 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 intentional fall-through cases, we have adopted a -pseudo-keyword macro 'fallthrough' which expands to gcc's extension -__attribute__((__fallthrough__)). `Statement Attributes -<https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html>`_ - -When the C17/C18 [[fallthrough]] syntax is more commonly supported by +implicit fall-through. In order to identify intentional fall-through +cases, we have adopted a pseudo-keyword macro "fallthrough" which +expands to gcc's extension `__attribute__((__fallthrough__)) +<https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html>`_. +(When the C17/C18 `[[fallthrough]]` syntax is more commonly supported by C compilers, static analyzers, and IDEs, we can switch to using that syntax -for the macro pseudo-keyword. +for the macro pseudo-keyword.) All switch/case blocks must end in one of: - break; - fallthrough; - continue; - goto <label>; - return [expression]; +* break; +* fallthrough; +* continue; +* goto <label>; +* return [expression]; |