linux-kernel - Re: Problems with arm64 compat vdso

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Message-Id: <20190924180634.206177-1-ndesaulniers@google.com>
Date:   Tue, 24 Sep 2019 11:06:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     vincenzo.frascino@....com
Cc:     ard.biesheuvel@...aro.org, catalin.marinas@....com,
        linux-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk, tglx@...utronix.de, will@...nel.org,
        natechancellor@...il.com
Subject: Re: Problems with arm64 compat vdso

Hi Vincenzo,
We also are having issues building the cross vDSO with Clang:
https://github.com/ClangBuiltLinux/linux/issues/595

It seems that `LINUXINCLUDE` in arch/arm64/kernel/vdso32/Makefile is including
arm64 headers in the arm part of the vdso32 build, which causes Clang to error
on the arm64 inline asm constraints being used in arm64.

I think if the issue Will described is fixed, it will be simpler for us to fix
the rest to get it to build w/ Clang.

https://github.com/ClangBuiltLinux/linux/issues/595#issuecomment-509874891
is the basis of such a patch.

Clang ships with all backends on by default, and uses a `-target <triple>` to
cross compile; so the idea of passing two cross compiler binaries for a compat
vDSO build doesn't really apply to Clang.