Messages in this thread Patch in this message | | | Date | Mon, 11 Feb 2019 16:01:09 +0100 | From | Jessica Yu <> | Subject | Re: [PATCH 3/3] include/linux/module.h: copy __init/__exit attrs to init/cleanup_module |
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+++ Miguel Ojeda [09/02/19 01:08 +0100]: >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. > >In particular, it triggers for all the init/cleanup_module >aliases in the kernel (defined by the module_init/exit macros), >ending up being very noisy. > >These aliases point to the __init/__exit functions of a module, >which are defined as __cold (among other attributes). However, >the aliases themselves do not have the __cold attribute. > >Since the compiler behaves differently when compiling a __cold >function as well as when compiling paths leading to calls >to __cold functions, the warning is trying to point out >the possibly-forgotten attribute in the alias. > >In order to keep the warning enabled, we decided to silence >this case. Ideally, we would mark the aliases directly >as __init/__exit. However, there are currently around 132 modules >in the kernel which are missing __init/__exit in their init/cleanup >functions (either because they are missing, or for other reasons, >e.g. the functions being called from somewhere else); and >a section mismatch is a hard error. > >A conservative alternative was to mark the aliases as __cold only. >However, since we would like to eventually enforce __init/__exit >to be always marked, we chose to use the new __copy function >attribute (introduced by GCC 9 as well to deal with this). >With it, we copy the attributes used by the target functions >into the aliases. This way, functions that were not marked >as __init/__exit won't have their aliases marked either, >and therefore there won't be a section mismatch. > >Note that the warning would go away marking either the extern >declaration, the definition, or both. However, we only mark >the definition of the alias, since we do not want callers >(which only see the declaration) to be compiled as if the function >was __cold (and therefore the paths leading to those calls >would be assumed to be unlikely). > >Link: https://lore.kernel.org/lkml/20190123173707.GA16603@gmail.com/ >Link: https://lore.kernel.org/lkml/20190206175627.GA20399@gmail.com/ >Suggested-by: Martin Sebor <msebor@gcc.gnu.org> >Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Acked-by: Jessica Yu <jeyu@kernel.org>
Thanks!
>--- > include/linux/module.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > >diff --git a/include/linux/module.h b/include/linux/module.h >index 8fa38d3e7538..f5bc4c046461 100644 >--- a/include/linux/module.h >+++ b/include/linux/module.h >@@ -129,13 +129,13 @@ extern void cleanup_module(void); > #define module_init(initfn) \ > static inline initcall_t __maybe_unused __inittest(void) \ > { return initfn; } \ >- int init_module(void) __attribute__((alias(#initfn))); >+ int init_module(void) __copy(initfn) __attribute__((alias(#initfn))); > > /* This is only required if you want to be unloadable. */ > #define module_exit(exitfn) \ > static inline exitcall_t __maybe_unused __exittest(void) \ > { return exitfn; } \ >- void cleanup_module(void) __attribute__((alias(#exitfn))); >+ void cleanup_module(void) __copy(exitfn) __attribute__((alias(#exitfn))); > > #endif > >-- >2.17.1 >
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