[v3,10/14] x86: prefer __section from compiler_attributes.h

Message ID 20190828225535.49592-11-ndesaulniers@google.com
State New
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Series
  • treewide: prefer __section from compiler_attributes.h
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Commit Message

Nick Desaulniers Aug. 28, 2019, 10:55 p.m.
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
Link: https://github.com/ClangBuiltLinux/linux/issues/619
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

Signed-off-by: Nick Desaulniers <ndesaulniers@google.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(-)

-- 
2.23.0.187.g17f5b7556c-goog

Comments

Miguel Ojeda Aug. 29, 2019, 2:14 p.m. | #1
On Thu, Aug 29, 2019 at 12:56 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>

> 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}

>  /*


I see other patches that reduce unused -> to __unused, but is this
unused -> __used intended?

Cheers,
Miguel
Miguel Ojeda Aug. 29, 2019, 2:22 p.m. | #2
On Thu, Aug 29, 2019 at 4:14 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>

> On Thu, Aug 29, 2019 at 12:56 AM Nick Desaulniers

> <ndesaulniers@google.com> wrote:

> >

> > 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}

> >  /*

>

> I see other patches that reduce unused -> to __unused, but is this


s/unused/other attrs like aligned and print/

Cheers,
Miguel

Patch

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[];