linux-kernel - Re: [PATCH 3/3] isystem: delete global -isystem compile option

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Date:   Mon, 2 Aug 2021 13:38:12 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, masahiroy@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 3/3] isystem: delete global -isystem compile option

On 8/2/2021 1:32 PM, Alexey Dobriyan wrote:
> On Mon, Aug 02, 2021 at 11:18:32AM -0700, Nathan Chancellor wrote:
>> On Sun, Aug 01, 2021 at 11:13:36PM +0300, Alexey Dobriyan wrote:
>>> In theory, it enables "leakage" of userspace headers into kernel which
>>> may present licensing problem.
>>>
>>> In practice, only stdarg.h was used, stdbool.h is trivial and SIMD
>>> intrinsics are contained to a few architectures and aren't global
>>> problem.
>>>
>>> In general, kernel is very self contained code and -isystem removal
>>> will further isolate it from Ring Threeland influence.
>>>
>>> nds32 keeps -isystem globally due to intrisics used in entrenched header.
>>>
>>> -isystem is selectively reenabled for some files.
>>>
>>> Not compile tested on hexagon.
>>
>> With this series on top of v5.14-rc4 and a tangential patch to fix
>> another issue, ARCH=hexagon defconfig and allmodconfig show no issues.
>>
>> Tested-by: Nathan Chancellor <nathan@...nel> # build (hexagon)
> 
> Oh wow, small miracle. Thank you!
> 
> Where can I find a cross-compiler? This link doesn't seem to have one
> https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/11.1.0/

Hexagon only builds with LLVM now because of the bump to require gcc 
4.9: https://lore.kernel.org/r/20210623141854.GA32155@lst.de/

Brian Cain has a link in that thread to an LLVM toolchain that works 
well for defconfig (allmodconfig requires LLVM 13/14 from git). 
Otherwise, https://apt.llvm.org or LLVM from your package manager should 
be sufficient for the same targets.

$ make -skj"$(nproc)" ARCH=hexagon CROSS_COMPILE=hexagon-linux-musl- 
LLVM=1 LLVM_IAS=1 defconfig all

should work fine as long as the bin folder for whatever toolchain you 
download is in your PATH.

Cheers,
Nathan