[PATCH 16/16] compiler_attributes.h: add note about __section

From: Nick Desaulniers <ndesaulniers@google.com>
To: akpm@linux-foundation.org
Cc: sedat.dilek@gmail.com, jpoimboe@redhat.com, yhs@fb.com,
	miguel.ojeda.sandonis@gmail.com,
	clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Subject: [PATCH 16/16] compiler_attributes.h: add note about __section
Date: Mon, 12 Aug 2019 14:50:49 -0700	[thread overview]
Message-ID: <20190812215052.71840-16-ndesaulniers@google.com> (raw)
In-Reply-To: <20190812215052.71840-1-ndesaulniers@google.com>

The antipattern described can be found with:
$ grep -e __section\(\" -r -e __section__\(\"

Link: https://bugs.llvm.org/show_bug.cgi?id=42950
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 include/linux/compiler_attributes.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 6b318efd8a74..f8c008d7f616 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -225,6 +225,16 @@
 #define __pure                          __attribute__((__pure__))
 
 /*
+ *  Note: Since this macro makes use of the "stringification operator" `#`, a
+ *        quoted string literal should not be passed to it. eg.
+ *        prefer:
+ *        __section(.foo)
+ *        to:
+ *        __section(".foo")
+ *        unless the section name is dynamically built up, in which case the
+ *        verbose __attribute__((__section__(".foo" x))) should be preferred.
+ *        See also: https://bugs.llvm.org/show_bug.cgi?id=42950
+ *
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
  * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
-- 
2.23.0.rc1.153.gdeed80330f-goog

