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Wed, 23 Jan 2019 09:38:25 -0800 (PST)
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Date: Wed, 23 Jan 2019 18:37:07 +0100
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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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To: Jessica Yu <jeyu@kernel.org>
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Cc: Laura Abbott <labbott@redhat.com>,
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Martin Sebor <msebor@gcc.gnu.org>, linux-kernel@vger.kernel.org
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Subject: [PATCH] include/linux/module.h: mark init/cleanup_module aliases as
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__cold
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Message-ID: <20190123173707.GA16603@gmail.com>
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The upcoming GCC 9 release adds the -Wmissing-attributes warnings
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(enabled by -Wall), which trigger for all the init/cleanup_module
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aliases in the kernel (defined by the module_init/exit macros),
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ending up being very noisy.
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These aliases point to the __init/__exit functions of a module,
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which are defined as __cold (among other attributes). However,
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the aliases themselves do not have the __cold attribute.
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Since the compiler behaves differently when compiling a __cold
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function as well as when compiling paths leading to calls
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to __cold functions, the warning is trying to point out
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the possibly-forgotten attribute in the alias.
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In order to keep the warning enabled, we choose to silence
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the warning by marking the aliases as __cold. This is possible
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marking either the extern declaration, the definition, or both.
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In order to avoid changing the behavior of callers, we do it
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only in the definition of the aliases (since those are not
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seen by any other TU).
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Suggested-by: Martin Sebor <msebor@gcc.gnu.org>
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Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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---
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Note that an alternative is using the new copy attribute
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introduced by GCC 9 (Martin told me about it, as well as the
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new warning).
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What I am concerned about using __copy is that I am not sure
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we should be copying all the attributes (even if some are
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blacklisted by the copy itself), since:
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- We have unknown-to-GCC attributes (e.g. from plugins).
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- We wouldn't enjoy the fix for older compilers
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(e.g. if the fix had an actual impact).
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So here I took the conservative approach for the moment,
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and we can discuss/apply whether another solution is best.
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Jessica: please review what I explain in the commit message.
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Do we actually want the __cold attribute in the declaration
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as well? If yes, AFAIK, GCC would assume paths that end up
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calling the __init/__exit functions are not meant to be taken
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(but when we are asked to load modules, that is the expected
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path, no?).
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I will put this in the compiler-attributes tree and get
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some time in linux-next, unless you want to pick it up!
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include/linux/module.h | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/include/linux/module.h b/include/linux/module.h
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index 8fa38d3e7538..c4e805e87628 100644
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--- a/include/linux/module.h
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+++ b/include/linux/module.h
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@@ -129,13 +129,13 @@ extern void cleanup_module(void);
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#define module_init(initfn) \
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static inline initcall_t __maybe_unused __inittest(void) \
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{ return initfn; } \
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- int init_module(void) __attribute__((alias(#initfn)));
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+ int init_module(void) __cold __attribute__((alias(#initfn)));
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/* This is only required if you want to be unloadable. */
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#define module_exit(exitfn) \
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static inline exitcall_t __maybe_unused __exittest(void) \
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{ return exitfn; } \
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- void cleanup_module(void) __attribute__((alias(#exitfn)));
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+ void cleanup_module(void) __cold __attribute__((alias(#exitfn)));
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#endif
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