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Date: Wed, 28 Aug 2019 11:59:46 +0200
From: Sedat Dilek <sedat.dilek@...il.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...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 ML <clang-built-linux@...glegroups.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/14] treewide: prefer __section from compiler_attributes.h
On Tue, Aug 27, 2019 at 10:40 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> 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.
>
> This fixes an Oops observed in distro's that use systemd and not
> net.core.bpf_jit_enable=1, when their kernels are compiled with Clang.
>
> 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
>
Hi Nick,
thanks for the v2 of your patch-series.
I just checked v2 on top of Linux v5.3-rc6...
sdi@...za:~/src/linux-kernel/linux$ grep -e __section\(\" -e __section__\(\" -r
include/linux/compiler_attributes.h: * __section(".foo")
include/linux/compiler_attributes.h: * verbose
__attribute__((__section__(".foo" x))) should be preferred.
OK: Description of the problem ^^
arch/sh/include/asm/cache.h:#define __read_mostly
__attribute__((__section__(".data..read_mostly")))
PATCH next-20190827 ^^
sh: prefer __section from compiler_attributes.h
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20190827&id=baf58858e8b6d853a7a8308901fcdd438e92a522
arch/arm64/kernel/smp_spin_table.c:volatile unsigned long
__section(".mmuoff.data.read")
arch/arm64/include/asm/cache.h:#define __read_mostly
__attribute__((__section__(".data..read_mostly")))
PATCH next-20190827 ^^
arm64: prefer __section from compiler_attributes.h
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20190827&id=80d838122643a09a9f99824adea4b4261e4451e6
arch/um/include/shared/init.h: __attribute__((__section__(".initcall"
level ".init"))) = fn
??? ^^
> See the discussions in:
> https://bugs.llvm.org/show_bug.cgi?id=42950
> https://marc.info/?l=linux-netdev&m=156412960619946&w=2
>
List CBL issue tracker to discussions:
https://github.com/ClangBuiltLinux/linux/issues/619
- Sedat -
> Changes V1 -> V2:
> * drop arm64, arc, and sh patches as they were picked up by their
> maintainers.
> * Split the previous V1 hunk from include/linux that touched
> include/linux/compiler.h off into its own patch for inclusion in
> stable, as it fixes a user visible issue.
> * Collect Acks and Tested by tags.
>
> Nick Desaulniers (14):
> s390/boot: prefer __section from compiler_attributes.h
> include/linux/compiler.h: prefer __section from compiler_attributes.h
> parisc: prefer __section from compiler_attributes.h
> um: prefer __section from compiler_attributes.h
> ia64: prefer __section from compiler_attributes.h
> arm: prefer __section from compiler_attributes.h
> mips: prefer __section from compiler_attributes.h
> sparc: prefer __section from compiler_attributes.h
> powerpc: prefer __section and __printf from compiler_attributes.h
> x86: prefer __section from compiler_attributes.h
> include/asm-generic: prefer __section from compiler_attributes.h
> include/linux: prefer __section from compiler_attributes.h
> include/linux/compiler.h: remove unused KENTRY macro
> compiler_attributes.h: add note about __section
>
> arch/arm/include/asm/cache.h | 2 +-
> arch/arm/include/asm/mach/arch.h | 4 ++--
> arch/arm/include/asm/setup.h | 2 +-
> arch/ia64/include/asm/cache.h | 2 +-
> arch/mips/include/asm/cache.h | 2 +-
> arch/parisc/include/asm/cache.h | 2 +-
> arch/parisc/include/asm/ldcw.h | 2 +-
> arch/powerpc/boot/main.c | 3 +--
> arch/powerpc/boot/ps3.c | 6 ++----
> arch/powerpc/include/asm/cache.h | 2 +-
> arch/powerpc/kernel/btext.c | 2 +-
> arch/s390/boot/startup.c | 2 +-
> arch/sparc/include/asm/cache.h | 2 +-
> arch/sparc/kernel/btext.c | 2 +-
> arch/um/kernel/um_arch.c | 6 +++---
> 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 +--
> include/asm-generic/error-injection.h | 2 +-
> include/asm-generic/kprobes.h | 5 ++---
> include/linux/cache.h | 6 +++---
> include/linux/compiler.h | 31 ++++-----------------------
> include/linux/compiler_attributes.h | 10 +++++++++
> include/linux/cpu.h | 2 +-
> include/linux/export.h | 2 +-
> include/linux/init_task.h | 4 ++--
> include/linux/interrupt.h | 5 ++---
> include/linux/sched/debug.h | 2 +-
> include/linux/srcutree.h | 2 +-
> 32 files changed, 54 insertions(+), 74 deletions(-)
>
> --
> 2.23.0.187.g17f5b7556c-goog
>
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