Compiler Attributes: add support for __copy (gcc >= 9)

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>
[sw0312.kim: cherry-pick stable linux-4.14.y commit b00c958ceb6c for gcc 9 build
 - change file path to include/linux/compiler.h instead of include/linux/compiler_types.h]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I0f0a016641391233166e04517ec70e24255d3ee9

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 65856c3599b4a56ed514ede4b795ef5e51b6dbc1..b5103ec2d52428b0a0c8f8340373cad94b5bebad 100644 (file)
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -209,6 +209,10 @@
 #endif
 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
 
+#if GCC_VERSION >= 90100
+#define __copy(symbol)                 __attribute__((__copy__(symbol)))
+#endif
+
 #endif /* gcc version >= 40000 specific checks */
 
 #if !defined(__noclone)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 2472740d7ab2201f58d68ce864448b3def30cdaf..7c14a55b365868300ef1371c71bfc0e77778d14d 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -288,6 +288,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 #define __cold
 #endif
 
+#ifndef __copy
+# define __copy(symbol)
+#endif
+
 /* Simple shorthand for a section definition */
 #ifndef __section
 # define __section(S) __attribute__ ((__section__(#S)))