linux-kernel - Re: [PATCH 19/19] arm64: vdso32: Enable Clang Compilation

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Message-ID: <0cee3707-d526-3766-3dde-543c8dbd8e68@arm.com>
Date:   Mon, 17 Feb 2020 12:26:16 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com, x86@...nel.org,
        catalin.marinas@....com, will.deacon@....com, arnd@...db.de,
        linux@...linux.org.uk, paul.burton@...s.com, tglx@...utronix.de,
        luto@...nel.org, mingo@...hat.com, bp@...en8.de, sboyd@...nel.org,
        salyzyn@...roid.com, pcc@...gle.com, 0x7f454c46@...il.com,
        ndesaulniers@...gle.com, avagin@...nvz.org
Subject: Re: [PATCH 19/19] arm64: vdso32: Enable Clang Compilation

Hi Nathan,

On 13/02/2020 18:44, Nathan Chancellor wrote:
> On Thu, Feb 13, 2020 at 04:16:14PM +0000, Vincenzo Frascino wrote:
>> Enable Clang Compilation for the vdso32 library.

[...]

>> +LD_COMPAT ?= $(CROSS_COMPILE_COMPAT)gcc
> 
> Well this is unfortunate :/
> 
> It looks like adding the --target flag to VDSO_LDFLAGS allows
> clang to link the vDSO just fine although it does warn that -nostdinc
> is unused:
> 
> clang-11: warning: argument unused during compilation: '-nostdinc'
> [-Wunused-command-line-argument]
>

This is why ended up in this "unfortunate" situation :) I wanted to avoid the
warning.

> It would be nice if the logic of commit fe00e50b2db8 ("ARM: 8858/1:
> vdso: use $(LD) instead of $(CC) to link VDSO") could be adopted here
> but I get that this Makefile is its own beast :) at the very least, I
> think that the --target flag should be added to VDSO_LDFLAGS so that gcc
> is not a requirement for this but I am curious if you tried that already
> and noticed any issues with it.
> 

--target is my preferred way as well, I can try to play another little bit with
the flags and see what I can come up with in the next version.

> Cheers,
> Nathan

[...]

-- 
Regards,
Vincenzo

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