Re: [PATCH v2 00/14] treewide: prefer __section from compiler_attributes.h

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	will@kernel.org, jpoimboe@redhat.com,
	naveen.n.rao@linux.vnet.ibm.com, davem@davemloft.net,
	paul.burton@mips.com,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 00/14] treewide: prefer __section from compiler_attributes.h
Date: Wed, 28 Aug 2019 11:59:46 +0200	[thread overview]
Message-ID: <CA+icZUVT8GJCPSSB=jLKLu=-OrWAj5W3Rkbx1ar0SGcEq0-D0g@mail.gmail.com> (raw)
In-Reply-To: <20190827204007.201890-1-ndesaulniers@google.com>

On Tue, Aug 27, 2019 at 10:40 PM Nick Desaulniers
<ndesaulniers@google.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@iniza:~/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
>