netdev - Re: [PATCH 00/16] treewide: prefer __section from compiler

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Date:   Mon, 19 Aug 2019 20:18:44 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     akpm@...ux-foundation.org, jpoimboe@...hat.com, yhs@...com,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH 00/16] treewide: prefer __section from compiler_attributes.h

On Mon, Aug 12, 2019 at 11:53 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
>
> See the discussions in:
> https://bugs.llvm.org/show_bug.cgi?id=42950
> https://marc.info/?l=linux-netdev&m=156412960619946&w=2
>
> Nick Desaulniers (16):
>   s390/boot: fix section name escaping
>   arc: prefer __section from compiler_attributes.h
>   parisc: prefer __section from compiler_attributes.h
>   um: prefer __section from compiler_attributes.h
>   sh: 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
>   arm64: 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
>

Hi Nick,

thanks for this patchset and the nice section names cleanup and simplification.

I have tested 5 relevant patches for my x86-64 Debian/buster system.

Patchset "for-5.3/x86-section-name-escaping" (5 patches):

compiler_attributes.h: add note about __section
include/linux/compiler.h: remove unused KENTRY macro
include/linux: prefer __section from compiler_attributes.h
include/asm-generic: prefer __section from compiler_attributes.h
x86: prefer __section from compiler_attributes.h

Toolchain: LLVM/Clang compiler and LLD linker version 9.0.0-rc2 (from
Debian/experimental)

I can boot on bare metal.

$ cat /proc/version
Linux version 5.3.0-rc5-1-amd64-cbl-asmgoto
(sedat.dilek@...il.com@...za) (clang version 9.0.0-+rc2-1~exp1
(tags/RELEASE_900/rc2)) #1~buster+dileks1 SMP 2019-08-19

I have sent by Tested-by to the single patches.

Have a nice day,
- Sedat -

>  arch/arc/include/asm/linkage.h        |  8 +++----
>  arch/arc/include/asm/mach_desc.h      |  3 +--
>  arch/arm/include/asm/cache.h          |  2 +-
>  arch/arm/include/asm/mach/arch.h      |  4 ++--
>  arch/arm/include/asm/setup.h          |  2 +-
>  arch/arm64/include/asm/cache.h        |  2 +-
>  arch/arm64/kernel/smp_spin_table.c    |  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/sh/include/asm/cache.h           |  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 +-
>  37 files changed, 62 insertions(+), 83 deletions(-)
>
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>