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Subject[PATCH 3/4] Documentation/process: Add fallthrough pseudo-keyword
Date
Describe the fallthrough pseudo-keyword.

Convert the coding-style.rst example to the keyword style.
Add description and links to deprecated.rst.

Signed-off-by: Joe Perches <joe@perches.com>
---
Documentation/process/coding-style.rst | 2 +-
Documentation/process/deprecated.rst | 33 +++++++++++++++++++++++----------
2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
index f4a2198187f9..ada573b7d703 100644
--- a/Documentation/process/coding-style.rst
+++ b/Documentation/process/coding-style.rst
@@ -56,7 +56,7 @@ instead of ``double-indenting`` the ``case`` labels. E.g.:
case 'K':
case 'k':
mem <<= 10;
- /* fall through */
+ fallthrough;
default:
break;
}
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index 56280e108d5a..a0ffdc8daef3 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -122,14 +122,27 @@ 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
+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.
+"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
+C compilers, static analyzers, and IDEs, we can switch to using that syntax
+for the macro pseudo-keyword.
+
+All switch/case blocks must end in one of:
+
+ break;
+ fallthrough;
+ continue;
+ goto <label>;
+ return [expression];
--
2.15.0
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