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kernel/Clean-the-new-GCC-9--Wmissing-attributes-warnings.patch

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Linux v5.0-rc6 Tweaks to gcc9 fixes
2019-02-11 14:16:56 +00:00
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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>,
Laura Abbott <labbott@redhat.com>,
Martin Sebor <msebor@gcc.gnu.org>,
Arnd Bergmann <arnd@arndb.de>,
Herbert Xu <herbert@gondor.apana.org.au>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>
Subject: [PATCH 1/3] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases
as __pure
Date: Sat, 9 Feb 2019 01:08:38 +0100
Message-Id: <20190209000840.11018-2-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 here because crc32_le_base/__crc32c_le_base
aren't __pure while their target crc32_le/__crc32c_le are.
These aliases are used by architectures as a fallback in accelerated
versions of CRC32. See commit 9784d82db3eb ("lib/crc32: make core crc32()
routines weak so they can be overridden").
Therefore, being fallbacks, it is likely that even if the aliases
were called from C, there wouldn't be any optimizations possible.
Currently, the only user is arm64, which calls this from asm.
Still, marking the aliases as __pure makes sense and is a good idea
for documentation purposes and possible future optimizations,
which also silences the warning.
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
---
lib/crc32.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/crc32.c b/lib/crc32.c
index 45b1d67a1767..4a20455d1f61 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -206,8 +206,8 @@ u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
EXPORT_SYMBOL(crc32_le);
EXPORT_SYMBOL(__crc32c_le);
-u32 crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
-u32 __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
+u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
+u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
/*
* This multiplies the polynomials x and y modulo the given modulus.
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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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Sean Christopherson <sean.j.christopherson@intel.com>
Subject: [PATCH 2/3] Compiler Attributes: add support for __copy (gcc >= 9)
Date: Sat, 9 Feb 2019 01:08:39 +0100
Message-Id: <20190209000840.11018-3-miguel.ojeda.sandonis@gmail.com>
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From the GCC manual:
copy
copy(function)
The copy attribute applies the set of attributes with which function
has been declared to the declaration of the function to which
the attribute is applied. The attribute is designed for libraries
that define aliases or function resolvers that are expected
to specify the same set of attributes as their targets. The copy
attribute can be used with functions, variables, or types. However,
the kind of symbol to which the attribute is applied (either
function or variable) must match the kind of symbol to which
the argument refers. The copy attribute copies only syntactic and
semantic attributes but not attributes that affect a symbol’s
linkage or visibility such as alias, visibility, or weak.
The deprecated attribute is also not copied.
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.:
void __cold f(void) {}
void __alias("f") g(void);
diagnoses:
warning: 'g' specifies less restrictive attribute than
its target 'f': 'cold' [-Wmissing-attributes]
Using __copy(f) we can copy the __cold attribute from f to g:
void __cold f(void) {}
void __copy(f) __alias("f") g(void);
This attribute is most useful to deal with situations where an alias
is declared but we don't know the exact attributes the target has.
For instance, in the kernel, the widely used module_init/exit macros
define the init/cleanup_module aliases, but those cannot be marked
always as __init/__exit since they some modules do not have their
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 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 19f32b0c29af..6b318efd8a74 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -34,6 +34,7 @@
#ifndef __has_attribute
# define __has_attribute(x) __GCC4_has_attribute_##x
# define __GCC4_has_attribute___assume_aligned__ (__GNUC_MINOR__ >= 9)
+# define __GCC4_has_attribute___copy__ 0
# define __GCC4_has_attribute___designated_init__ 0
# define __GCC4_has_attribute___externally_visible__ 1
# define __GCC4_has_attribute___noclone__ 1
@@ -100,6 +101,19 @@
*/
#define __attribute_const__ __attribute__((__const__))
+/*
+ * Optional: only supported since gcc >= 9
+ * Optional: not supported by clang
+ * Optional: not supported by icc
+ *
+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
+ */
+#if __has_attribute(__copy__)
+# define __copy(symbol) __attribute__((__copy__(symbol)))
+#else
+# define __copy(symbol)
+#endif
+
/*
* Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
* attribute warnings entirely and for good") for more information.
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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
To: Jessica Yu <jeyu@kernel.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
Laura Abbott <labbott@redhat.com>,
Martin Sebor <msebor@gcc.gnu.org>,
Arnd Bergmann <arnd@arndb.de>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
James Morris <james.morris@microsoft.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Borislav Petkov <bp@suse.de>,
Kees Cook <keescook@chromium.org>,
Matt Mullins <mmullins@fb.com>,
Vincent Whitchurch <vincent.whitchurch@axis.com>,
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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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
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