From: Miguel Ojeda miguel.ojeda.sandonis@gmail.com
commit c0d9782f5b6d7157635ae2fd782a4b27d55a6013 upstream.
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 some modules do not have their functions marked as such.
Suggested-by: Martin Sebor msebor@gcc.gnu.org Reviewed-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Miguel Ojeda miguel.ojeda.sandonis@gmail.com Signed-off-by: Stefan Agner stefan@agner.ch Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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)) #endif
+#if GCC_VERSION >= 90100 +#define __copy(symbol) __attribute__((__copy__(symbol))) +#endif + #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 #endif
+#ifndef __copy +# define __copy(symbol) +#endif + #ifndef __randomize_layout # define __randomize_layout __designated_init #endif