[PATCH v3 1/9] Compiler Attributes: Add __must_init macro

[Ian Rogers <irogers@google.com>]

Clang supports the 'require_explicit_initialization' attribute on struct
fields to indicate that a field must be initialized explicitly by the
user when the object is constructed. When an aggregate initializer or
uninitialized variable omits an annotated field, Clang emits a
-Wuninitialized-explicit-init warning (enabled by default).

Add the __must_init macro to include/linux/compiler_attributes.h (which
is included by include/linux/compiler_types.h and
include/linux/compiler.h) so kernel structs with error-prone
initialization (such as mandatory callbacks or cleanup handlers) can
enforce explicit initialization at compile time, as discussed at the
Linux Plumbers Conference. The shorter __must_init spelling, rather than
the attribute's full name, keeps annotated struct members readable and
was suggested by Greg Kroah-Hartman.

Note that Clang versions prior to the fix for
https://github.com/llvm/llvm-project/issues/232483 do not diagnose
file-scope objects declared without any initializer (initializers at
file scope that omit the field are diagnosed).

Also teach Sphinx (Documentation/conf.py), kernel-doc
(tools/lib/python/kdoc/xforms_lists.py), and checkpatch.pl about the new
attribute macro.

Link: https://lpc.events/event/20/contributions/2392/
Link: https://lore.kernel.org/lkml/2026101532-fantastic-deafness-e04c@gregkh/
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 Documentation/conf.py                 |  1 +
 include/linux/compiler_attributes.h   | 12 ++++++++++++
 scripts/checkpatch.pl                 |  1 +
 tools/lib/python/kdoc/xforms_lists.py |  1 +
 4 files changed, 15 insertions(+)

diff --git a/Documentation/conf.py b/Documentation/conf.py
index 5ab26ce89daf..baaa4035258c 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -203,6 +203,7 @@ c_id_attributes = [
     "__noreturn",
     "__packed",
     "__pure",
+    "__must_init",
     "__section",
     "__always_unused",
     "__maybe_unused",
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 476c4c560d17..b9c0b56dd22e 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -322,6 +322,18 @@
  */
 #define __pure                          __attribute__((__pure__))
 
+/*
+ * Optional: not supported by gcc
+ * Optional: only supported since clang >= 20.0
+ *
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#require-explicit-initialization
+ */
+#if __has_attribute(__require_explicit_initialization__)
+# define __must_init __attribute__((__require_explicit_initialization__))
+#else
+# define __must_init
+#endif
+
 /*
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b8b64f720191..6a091c45b1a1 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6888,6 +6888,7 @@ sub process {
 				"noreturn"			=> "__noreturn",
 				"packed"			=> "__packed",
 				"pure"				=> "__pure",
+				"require_explicit_initialization" => "__must_init",
 				"section"			=> "__section",
 				"used"				=> "__used",
 				"weak"				=> "__weak"
diff --git a/tools/lib/python/kdoc/xforms_lists.py b/tools/lib/python/kdoc/xforms_lists.py
index db23fb650ea8..42956b98aae3 100644
--- a/tools/lib/python/kdoc/xforms_lists.py
+++ b/tools/lib/python/kdoc/xforms_lists.py
@@ -36,6 +36,7 @@ class CTransforms:
         (CMatch("CRYPTO_MINALIGN_ATTR"), ""),
         (CMatch("__private"), ""),
         (CMatch("__rcu"), ""),
+        (CMatch("__must_init"), ""),
         (CMatch("____cacheline_aligned_in_smp"), ""),
         (CMatch("____cacheline_aligned"), ""),
         (CMatch("__cacheline_group_(?:begin|end)"), ""),
-- 
2.56.0.455.g6c5a503b38-goog