linux-kernel - Re: [PATCH] x86/Kconfig: Allow X86_X32_ABI with llvm-objcopy in some cases

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Date:   Tue, 5 Jul 2022 17:09:21 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        Nathan Chancellor <nathan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        llvm@...ts.linux.dev
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/Kconfig: Allow X86_X32_ABI with llvm-objcopy in some
 cases

On 7/1/22 14:04, Alex Xu (Hello71) wrote:
> According to the comment and commit message, there are issues compiling
> with IBT and/or compressed debug sections. Therefore, the condition
> should be restricted to when those are enabled.

This whole situation is gross.  We code in the vDSO that needs to 
dereference a genuinely 64-bit pointer.  The x32 toolchain doesn't 
understand this, so we have a massive hack using objcopy.  I see a few 
solutions:

1. Keep the hack alive, with further hacks like this patch.

2. Drop the x32 vDSO.

3. Drop x32.

4. Get gcc and/or clang to add actual support for this.

I admit I'm partial to solution #3.  I wonder how practical #4 is.

--Andy