linux-kernel - Re: [PATCH v4 mips-next 0/7] MIPS: vmlinux.lds.S sections fixes & cleanup

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Date:   Sat, 09 Jan 2021 17:22:36 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Alexander Lobakin <alobakin@...me>, Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Pei Huang <huangpei@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Corey Minyard <cminyard@...sta.com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, stable@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v4 mips-next 0/7] MIPS: vmlinux.lds.S sections fixes & cleanup

From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Date: Sat, 9 Jan 2021 12:12:59 +0100

> On Thu, Jan 07, 2021 at 12:33:38PM +0000, Alexander Lobakin wrote:
>> This series hunts the problems discovered after manual enabling of
>> ARCH_WANT_LD_ORPHAN_WARN. Notably:
>>  - adds the missing PAGE_ALIGNED_DATA() section affecting VDSO
>>    placement (marked for stable);
>>  - properly stops .eh_frame section generation.
>>
>> Compile and runtime tested on MIPS32R2 CPS board with no issues
>> using two different toolkits:
>>  - Binutils 2.35.1, GCC 10.2.0;
>>  - LLVM stack 11.0.0.
>>
>> Since v3 [2]:
>>  - fix the third patch as GNU stack emits .rel.dyn into VDSO for
>>    some reason if .cfi_sections is specified.
>>
>> Since v2 [1]:
>>  - stop discarding .eh_frame and just prevent it from generating
>>    (Kees);
>>  - drop redundant sections assertions (Fangrui);
>>  - place GOT table in .text instead of asserting as it's not empty
>>    when building with LLVM (Nathan);
>>  - catch compound literals in generic definitions when building with
>>    LD_DEAD_CODE_DATA_ELIMINATION (Kees);
>>  - collect two Reviewed-bys (Kees).
>>
>> Since v1 [0]:
>>  - catch .got entries too as LLD may produce it (Nathan);
>>  - check for unwanted sections to be zero-sized instead of
>>    discarding (Fangrui).
>>
>> [0] https://lore.kernel.org/linux-mips/20210104121729.46981-1-alobakin@pm.me
>> [1] https://lore.kernel.org/linux-mips/20210106200713.31840-1-alobakin@pm.me
>> [2] https://lore.kernel.org/linux-mips/20210107115120.281008-1-alobakin@pm.me
>>
>> Alexander Lobakin (7):
>>   MIPS: vmlinux.lds.S: add missing PAGE_ALIGNED_DATA() section
>>   MIPS: vmlinux.lds.S: add ".gnu.attributes" to DISCARDS
>>   MIPS: properly stop .eh_frame generation
>>   MIPS: vmlinux.lds.S: catch bad .rel.dyn at link time
>>   MIPS: vmlinux.lds.S: explicitly declare .got table
>>   vmlinux.lds.h: catch compound literals into data and BSS
>>   MIPS: select ARCH_WANT_LD_ORPHAN_WARN
>
> this breaks my builds:
>
>   LD      vmlinux.o
>   MODPOST vmlinux.symvers
>   MODINFO modules.builtin.modinfo
>   GEN     modules.builtin
>   LD      .tmp_vmlinux.kallsyms1
> mips64-linux-gnu-ld: Unexpected run-time relocations (.rel) detected!

I think they should be handled as it's done for ARM64 [0]. Will do v5
soon.

[0] https://elixir.bootlin.com/linux/v5.11-rc2/source/arch/arm64/kernel/vmlinux.lds.S#L219

> $ mips64-linux-gnu-ld --version
> GNU ld version 2.27-3.fc24
>
> $ mips64-linux-gnu-gcc --version
> mips64-linux-gnu-gcc (GCC) 6.1.1 20160621 (Red Hat Cross 6.1.1-2)
>
> Thomas.

Thanks,
Alex

> --
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]