queue-4.19/include-linux-module.h-copy-__init-__exit-attrs-to-init-cleanup_module.patch

   1 From a6e60d84989fa0e91db7f236eda40453b0e44afa Mon Sep 17 00:00:00 2001
   2 From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
   3 Date: Sat, 19 Jan 2019 20:59:34 +0100
   4 Subject: include/linux/module.h: copy __init/__exit attrs to init/cleanup_module
   5
   6 From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
   7
   8 commit a6e60d84989fa0e91db7f236eda40453b0e44afa upstream.
   9
  10 The upcoming GCC 9 release extends the -Wmissing-attributes warnings
  11 (enabled by -Wall) to C and aliases: it warns when particular function
  12 attributes are missing in the aliases but not in their target.
  13
  14 In particular, it triggers for all the init/cleanup_module
  15 aliases in the kernel (defined by the module_init/exit macros),
  16 ending up being very noisy.
  17
  18 These aliases point to the __init/__exit functions of a module,
  19 which are defined as __cold (among other attributes). However,
  20 the aliases themselves do not have the __cold attribute.
  21
  22 Since the compiler behaves differently when compiling a __cold
  23 function as well as when compiling paths leading to calls
  24 to __cold functions, the warning is trying to point out
  25 the possibly-forgotten attribute in the alias.
  26
  27 In order to keep the warning enabled, we decided to silence
  28 this case. Ideally, we would mark the aliases directly
  29 as __init/__exit. However, there are currently around 132 modules
  30 in the kernel which are missing __init/__exit in their init/cleanup
  31 functions (either because they are missing, or for other reasons,
  32 e.g. the functions being called from somewhere else); and
  33 a section mismatch is a hard error.
  34
  35 A conservative alternative was to mark the aliases as __cold only.
  36 However, since we would like to eventually enforce __init/__exit
  37 to be always marked,  we chose to use the new __copy function
  38 attribute (introduced by GCC 9 as well to deal with this).
  39 With it, we copy the attributes used by the target functions
  40 into the aliases. This way, functions that were not marked
  41 as __init/__exit won't have their aliases marked either,
  42 and therefore there won't be a section mismatch.
  43
  44 Note that the warning would go away marking either the extern
  45 declaration, the definition, or both. However, we only mark
  46 the definition of the alias, since we do not want callers
  47 (which only see the declaration) to be compiled as if the function
  48 was __cold (and therefore the paths leading to those calls
  49 would be assumed to be unlikely).
  50
  51 Link: https://lore.kernel.org/lkml/20190123173707.GA16603@gmail.com/
  52 Link: https://lore.kernel.org/lkml/20190206175627.GA20399@gmail.com/
  53 Suggested-by: Martin Sebor <msebor@gcc.gnu.org>
  54 Acked-by: Jessica Yu <jeyu@kernel.org>
  55 Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
  56 Signed-off-by: Stefan Agner <stefan@agner.ch>
  57 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  58
  59 ---
  60  include/linux/module.h |    4 ++--
  61  1 file changed, 2 insertions(+), 2 deletions(-)
  62
  63 --- a/include/linux/module.h
  64 +++ b/include/linux/module.h
  65 @@ -130,13 +130,13 @@ extern void cleanup_module(void);
  66  #define module_init(initfn)                                    \
  67         static inline initcall_t __maybe_unused __inittest(void)                \
  68         { return initfn; }                                      \
  69 -       int init_module(void) __attribute__((alias(#initfn)));
  70 +       int init_module(void) __copy(initfn) __attribute__((alias(#initfn)));
  71
  72  /* This is only required if you want to be unloadable. */
  73  #define module_exit(exitfn)                                    \
  74         static inline exitcall_t __maybe_unused __exittest(void)                \
  75         { return exitfn; }                                      \
  76 -       void cleanup_module(void) __attribute__((alias(#exitfn)));
  77 +       void cleanup_module(void) __copy(exitfn) __attribute__((alias(#exitfn)));
  78
  79  #endif
  80