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d04b89dc GKH |
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 |