linux-kernel - [PATCH v2 10/14] x86: prefer __section from compiler

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Message-Id: <20190827204007.201890-11-ndesaulniers@google.com>
Date:   Tue, 27 Aug 2019 13:40:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     miguel.ojeda.sandonis@...il.com
Cc:     sedat.dilek@...il.com, will@...nel.org, jpoimboe@...hat.com,
        naveen.n.rao@...ux.vnet.ibm.com, davem@...emloft.net,
        paul.burton@...s.com, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 10/14] x86: prefer __section from compiler_attributes.h

GCC unescapes escaped string section names while Clang does not. Because
__section uses the `#` stringification operator for the section name, it
doesn't need to be escaped.

Instead, we should:
1. Prefer __section(.section_name_no_quotes).
2. Only use __attribute__((__section(".section"))) when creating the
section name via C preprocessor (see the definition of __define_initcall
in arch/um/include/shared/init.h).

This antipattern was found with:
$ grep -e __section\(\" -e __section__\(\" -r

See the discussions in:
Link: https://bugs.llvm.org/show_bug.cgi?id=42950
Link: https://marc.info/?l=linux-netdev&m=156412960619946&w=2
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 arch/x86/include/asm/cache.h       | 2 +-
 arch/x86/include/asm/intel-mid.h   | 2 +-
 arch/x86/include/asm/iommu_table.h | 5 ++---
 arch/x86/include/asm/irqflags.h    | 2 +-
 arch/x86/include/asm/mem_encrypt.h | 2 +-
 arch/x86/kernel/cpu/cpu.h          | 3 +--
 6 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/cache.h b/arch/x86/include/asm/cache.h
index abe08690a887..bb9f4bf4ec02 100644
--- a/arch/x86/include/asm/cache.h
+++ b/arch/x86/include/asm/cache.h
@@ -8,7 +8,7 @@
 #define L1_CACHE_SHIFT	(CONFIG_X86_L1_CACHE_SHIFT)
 #define L1_CACHE_BYTES	(1 << L1_CACHE_SHIFT)
 
-#define __read_mostly __attribute__((__section__(".data..read_mostly")))
+#define __read_mostly __section(.data..read_mostly)
 
 #define INTERNODE_CACHE_SHIFT CONFIG_X86_INTERNODE_CACHE_SHIFT
 #define INTERNODE_CACHE_BYTES (1 << INTERNODE_CACHE_SHIFT)
diff --git a/arch/x86/include/asm/intel-mid.h b/arch/x86/include/asm/intel-mid.h
index 8e5af119dc2d..f51f04aefe1b 100644
--- a/arch/x86/include/asm/intel-mid.h
+++ b/arch/x86/include/asm/intel-mid.h
@@ -43,7 +43,7 @@ struct devs_id {
 
 #define sfi_device(i)								\
 	static const struct devs_id *const __intel_mid_sfi_##i##_dev __used	\
-	__attribute__((__section__(".x86_intel_mid_dev.init"))) = &i
+	__section(.x86_intel_mid_dev.init) = &i
 
 /**
 * struct mid_sd_board_info - template for SD device creation
diff --git a/arch/x86/include/asm/iommu_table.h b/arch/x86/include/asm/iommu_table.h
index 1fb3fd1a83c2..7d190710eb92 100644
--- a/arch/x86/include/asm/iommu_table.h
+++ b/arch/x86/include/asm/iommu_table.h
@@ -50,9 +50,8 @@ struct iommu_table_entry {
 
 #define __IOMMU_INIT(_detect, _depend, _early_init, _late_init, _finish)\
 	static const struct iommu_table_entry				\
-		__iommu_entry_##_detect __used				\
-	__attribute__ ((unused, __section__(".iommu_table"),		\
-			aligned((sizeof(void *)))))	\
+		__iommu_entry_##_detect __used __section(.iommu_table)	\
+		__aligned((sizeof(void *)))				\
 	= {_detect, _depend, _early_init, _late_init,			\
 	   _finish ? IOMMU_FINISH_IF_DETECTED : 0}
 /*
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index 8a0e56e1dcc9..68db90bca813 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -9,7 +9,7 @@
 #include <asm/nospec-branch.h>
 
 /* Provide __cpuidle; we can't safely include <linux/cpu.h> */
-#define __cpuidle __attribute__((__section__(".cpuidle.text")))
+#define __cpuidle __section(.cpuidle.text)
 
 /*
  * Interrupt control:
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 0c196c47d621..db2cd3709148 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -50,7 +50,7 @@ void __init mem_encrypt_free_decrypted_mem(void);
 bool sme_active(void);
 bool sev_active(void);
 
-#define __bss_decrypted __attribute__((__section__(".bss..decrypted")))
+#define __bss_decrypted __section(.bss..decrypted)
 
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
 
diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index c0e2407abdd6..7ff9dc41a603 100644
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -38,8 +38,7 @@ struct _tlb_table {
 
 #define cpu_dev_register(cpu_devX) \
 	static const struct cpu_dev *const __cpu_dev_##cpu_devX __used \
-	__attribute__((__section__(".x86_cpu_dev.init"))) = \
-	&cpu_devX;
+	__section(.x86_cpu_dev.init) = &cpu_devX;
 
 extern const struct cpu_dev *const __x86_cpu_dev_start[],
 			    *const __x86_cpu_dev_end[];
-- 
2.23.0.187.g17f5b7556c-goog