[PATCH 4.14 64/69] Compiler Attributes: add support for __copy (gcc >= 9)

From: Greg Kroah-Hartman
Date: Fri Jun 07 2019 - 11:47:15 EST

From: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>

commit c0d9782f5b6d7157635ae2fd782a4b27d55a6013 upstream.

>From the GCC manual:


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 symbolâs
linkage or visibility such as alias, visibility, or weak.
The deprecated attribute is also not copied.


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);


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 some modules do not have their
functions marked as such.

Suggested-by: Martin Sebor <msebor@xxxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>
Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Changes in v2:
- Fix define of compatibility __copy macro (add symbol argument)

include/linux/compiler-gcc.h | 4 ++++
include/linux/compiler_types.h | 4 ++++
2 files changed, 8 insertions(+)

--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -343,6 +343,10 @@
#define __designated_init __attribute__((designated_init))

+#if GCC_VERSION >= 90100
+#define __copy(symbol) __attribute__((__copy__(symbol)))
#endif /* gcc version >= 40000 specific checks */

#if !defined(__noclone)
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -230,6 +230,10 @@ struct ftrace_likely_data {
# define __latent_entropy

+#ifndef __copy
+# define __copy(symbol)
#ifndef __randomize_layout
# define __randomize_layout __designated_init