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Subject[PATCH 2/3] Compiler Attributes: add support for __copy (gcc >= 9)
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From the GCC manual:

copy
copy(function)

The copy attribute applies the set of attributes with which function
has been declared to the declaration of the function to which
the attribute is applied. The attribute is designed for libraries
that define aliases or function resolvers that are expected
to specify the same set of attributes as their targets. The copy
attribute can be used with functions, variables, or types. However,
the kind of symbol to which the attribute is applied (either
function or variable) must match the kind of symbol to which
the argument refers. The copy attribute copies only syntactic and
semantic attributes but not attributes that affect a symbol’s
linkage or visibility such as alias, visibility, or weak.
The deprecated attribute is also not copied.

https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

The upcoming GCC 9 release extends the -Wmissing-attributes warnings
(enabled by -Wall) to C and aliases: it warns when particular function
attributes are missing in the aliases but not in their target, e.g.:

void __cold f(void) {}
void __alias("f") g(void);

diagnoses:

warning: 'g' specifies less restrictive attribute than
its target 'f': 'cold' [-Wmissing-attributes]

Using __copy(f) we can copy the __cold attribute from f to g:

void __cold f(void) {}
void __copy(f) __alias("f") g(void);

This attribute is most useful to deal with situations where an alias
is declared but we don't know the exact attributes the target has.

For instance, in the kernel, the widely used module_init/exit macros
define the init/cleanup_module aliases, but those cannot be marked
always as __init/__exit since they some modules do not have their
functions marked as such.

Suggested-by: Martin Sebor <msebor@gcc.gnu.org>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
---
include/linux/compiler_attributes.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 19f32b0c29af..6b318efd8a74 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -34,6 +34,7 @@
#ifndef __has_attribute
# define __has_attribute(x) __GCC4_has_attribute_##x
# define __GCC4_has_attribute___assume_aligned__ (__GNUC_MINOR__ >= 9)
+# define __GCC4_has_attribute___copy__ 0
# define __GCC4_has_attribute___designated_init__ 0
# define __GCC4_has_attribute___externally_visible__ 1
# define __GCC4_has_attribute___noclone__ 1
@@ -100,6 +101,19 @@
*/
#define __attribute_const__ __attribute__((__const__))

+/*
+ * Optional: only supported since gcc >= 9
+ * Optional: not supported by clang
+ * Optional: not supported by icc
+ *
+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
+ */
+#if __has_attribute(__copy__)
+# define __copy(symbol) __attribute__((__copy__(symbol)))
+#else
+# define __copy(symbol)
+#endif
+
/*
* Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
* attribute warnings entirely and for good") for more information.
--
2.17.1
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