451 lines
21 KiB
Diff
451 lines
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From patchwork Sat Feb 9 00:08:38 2019
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Fri, 08 Feb 2019 16:09:04 -0800 (PST)
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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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To: linux-kernel@vger.kernel.org
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Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
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Laura Abbott <labbott@redhat.com>,
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Martin Sebor <msebor@gcc.gnu.org>,
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Arnd Bergmann <arnd@arndb.de>,
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Herbert Xu <herbert@gondor.apana.org.au>,
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Ard Biesheuvel <ard.biesheuvel@linaro.org>,
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Krzysztof Kozlowski <krzk@kernel.org>,
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Catalin Marinas <catalin.marinas@arm.com>
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Subject: [PATCH 1/3] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases
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as __pure
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Date: Sat, 9 Feb 2019 01:08:38 +0100
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Message-Id: <20190209000840.11018-2-miguel.ojeda.sandonis@gmail.com>
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In-Reply-To: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
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References: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Precedence: bulk
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List-ID: <linux-kernel.vger.kernel.org>
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The upcoming GCC 9 release extends the -Wmissing-attributes warnings
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(enabled by -Wall) to C and aliases: it warns when particular function
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attributes are missing in the aliases but not in their target.
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In particular, it triggers here because crc32_le_base/__crc32c_le_base
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aren't __pure while their target crc32_le/__crc32c_le are.
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These aliases are used by architectures as a fallback in accelerated
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versions of CRC32. See commit 9784d82db3eb ("lib/crc32: make core crc32()
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routines weak so they can be overridden").
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Therefore, being fallbacks, it is likely that even if the aliases
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were called from C, there wouldn't be any optimizations possible.
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Currently, the only user is arm64, which calls this from asm.
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Still, marking the aliases as __pure makes sense and is a good idea
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for documentation purposes and possible future optimizations,
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which also silences the warning.
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Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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Tested-by: Laura Abbott <labbott@redhat.com>
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Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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---
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lib/crc32.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/lib/crc32.c b/lib/crc32.c
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index 45b1d67a1767..4a20455d1f61 100644
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--- a/lib/crc32.c
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+++ b/lib/crc32.c
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@@ -206,8 +206,8 @@ u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
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EXPORT_SYMBOL(crc32_le);
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EXPORT_SYMBOL(__crc32c_le);
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-u32 crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
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-u32 __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
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+u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
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+u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
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/*
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* This multiplies the polynomials x and y modulo the given modulus.
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From patchwork Sat Feb 9 00:08:39 2019
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Fri, 08 Feb 2019 16:09:05 -0800 (PST)
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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
|
||
To: linux-kernel@vger.kernel.org
|
||
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
|
||
Martin Sebor <msebor@gcc.gnu.org>,
|
||
Arnd Bergmann <arnd@arndb.de>,
|
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Laura Abbott <labbott@redhat.com>,
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Nick Desaulniers <ndesaulniers@google.com>,
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Kees Cook <keescook@chromium.org>,
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Sean Christopherson <sean.j.christopherson@intel.com>
|
||
Subject: [PATCH 2/3] Compiler Attributes: add support for __copy (gcc >= 9)
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||
Date: Sat, 9 Feb 2019 01:08:39 +0100
|
||
Message-Id: <20190209000840.11018-3-miguel.ojeda.sandonis@gmail.com>
|
||
In-Reply-To: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
|
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References: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
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From the GCC manual:
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copy
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copy(function)
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The copy attribute applies the set of attributes with which function
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has been declared to the declaration of the function to which
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the attribute is applied. The attribute is designed for libraries
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that define aliases or function resolvers that are expected
|
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to specify the same set of attributes as their targets. The copy
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attribute can be used with functions, variables, or types. However,
|
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the kind of symbol to which the attribute is applied (either
|
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function or variable) must match the kind of symbol to which
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the argument refers. The copy attribute copies only syntactic and
|
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semantic attributes but not attributes that affect a symbol’s
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linkage or visibility such as alias, visibility, or weak.
|
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The deprecated attribute is also not copied.
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||
|
||
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.:
|
||
|
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void __cold f(void) {}
|
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void __alias("f") g(void);
|
||
|
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diagnoses:
|
||
|
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warning: 'g' specifies less restrictive attribute than
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its target 'f': 'cold' [-Wmissing-attributes]
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Using __copy(f) we can copy the __cold attribute from f to g:
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||
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void __cold f(void) {}
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void __copy(f) __alias("f") g(void);
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||
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This attribute is most useful to deal with situations where an alias
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is declared but we don't know the exact attributes the target has.
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For instance, in the kernel, the widely used module_init/exit macros
|
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define the init/cleanup_module aliases, but those cannot be marked
|
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always as __init/__exit since they some modules do not have their
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functions marked as such.
|
||
|
||
Suggested-by: Martin Sebor <msebor@gcc.gnu.org>
|
||
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
|
||
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
|
||
---
|
||
include/linux/compiler_attributes.h | 14 ++++++++++++++
|
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1 file changed, 14 insertions(+)
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diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
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index 19f32b0c29af..6b318efd8a74 100644
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--- a/include/linux/compiler_attributes.h
|
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+++ b/include/linux/compiler_attributes.h
|
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@@ -34,6 +34,7 @@
|
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#ifndef __has_attribute
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# define __has_attribute(x) __GCC4_has_attribute_##x
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# define __GCC4_has_attribute___assume_aligned__ (__GNUC_MINOR__ >= 9)
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+# define __GCC4_has_attribute___copy__ 0
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# define __GCC4_has_attribute___designated_init__ 0
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# define __GCC4_has_attribute___externally_visible__ 1
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# define __GCC4_has_attribute___noclone__ 1
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@@ -100,6 +101,19 @@
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*/
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#define __attribute_const__ __attribute__((__const__))
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+/*
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+ * Optional: only supported since gcc >= 9
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+ * Optional: not supported by clang
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||
+ * Optional: not supported by icc
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+ *
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+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
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+ */
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+#if __has_attribute(__copy__)
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+# define __copy(symbol) __attribute__((__copy__(symbol)))
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+#else
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+# define __copy(symbol)
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+#endif
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+
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/*
|
||
* Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
|
||
* attribute warnings entirely and for good") for more information.
|
||
|
||
From patchwork Sat Feb 9 00:08:40 2019
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Fri, 08 Feb 2019 16:09:06 -0800 (PST)
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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: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
|
||
Laura Abbott <labbott@redhat.com>,
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Martin Sebor <msebor@gcc.gnu.org>,
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Arnd Bergmann <arnd@arndb.de>,
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Masahiro Yamada <yamada.masahiro@socionext.com>,
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James Morris <james.morris@microsoft.com>,
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Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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Borislav Petkov <bp@suse.de>,
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Matt Mullins <mmullins@fb.com>,
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Vincent Whitchurch <vincent.whitchurch@axis.com>,
|
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WANG Chao <chao.wang@ucloud.cn>, linux-kernel@vger.kernel.org
|
||
Subject: [PATCH 3/3] include/linux/module.h: copy __init/__exit attrs to
|
||
init/cleanup_module
|
||
Date: Sat, 9 Feb 2019 01:08:40 +0100
|
||
Message-Id: <20190209000840.11018-4-miguel.ojeda.sandonis@gmail.com>
|
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In-Reply-To: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
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References: <20190209000840.11018-1-miguel.ojeda.sandonis@gmail.com>
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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>
|
||
---
|
||
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
|
||
|