linux-kernel - Re: [PATCH v2 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress .eh

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Date:   Mon, 24 Feb 2020 16:28:44 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>, m@...ntu-m2-xlarge-x86
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Michael Matz <matz@...e.de>, Fangrui Song <maskray@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to
 suppress .eh_frame sections

On Mon, Feb 24, 2020 at 06:21:28PM -0500, Arvind Sankar wrote:
> While discussing a patch to discard .eh_frame from the compressed
> vmlinux using the linker script, Fangrui Song pointed out [1] that these
> sections shouldn't exist in the first place because arch/x86/Makefile
> uses -fno-asynchronous-unwind-tables.
> 
> It turns out this is because the Makefiles used to build the compressed
> kernel redefine KBUILD_CFLAGS, dropping this flag.
> 
> Add the flag to the Makefile for the compressed kernel, as well as the
> EFI stub Makefile to fix this.
> 
> Also add the flag to boot/Makefile and realmode/rm/Makefile so that the
> kernel's boot code (boot/setup.elf) and realmode trampoline
> (realmode/rm/realmode.elf) won't be compiled with .eh_frame sections,
> since their linker scripts also just discard it.
> 
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> Suggested-By: Fangrui Song <maskray@...gle.com>
> [1] https://lore.kernel.org/lkml/20200222185806.ywnqhfqmy67akfsa@google.com/

My previous review conments still stand,

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>