linux-kernel - Re: [PATCH] x86/tools/relocs: Add _etext and __end_of_kernel_reserve to S

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Message-ID: <20200111173214.GB2688392@rani.riverdale.lan>
Date:   Sat, 11 Jan 2020 12:32:14 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>
Subject: Re: [PATCH] x86/tools/relocs: Add _etext and __end_of_kernel_reserve
 to S_REL

On Sat, Jan 11, 2020 at 12:20:48PM -0500, Arvind Sankar wrote:
> I'm running gentoo, but building the kernel using binutils-2.21.1
> compiled from the GNU source tarball, and gcc-4.6.4 again compiled from
> source. (It's not something I normally need but I was investigating
> something else to see what exactly happens with older toolchains.)
> 
> I used the below to compile the kernel (I added in
> readelf/objdump/objcopy just now, and it does build until the relocs
> error). The config is x86-64 defconfig with CONFIG_RETPOLINE overridden
> to n (since gcc 4.6.4 doesn't support retpoline).
> 
> make O=~/kernel64 -j LD=~/old/bin/ld AS=~/old/bin/as READELF=~/old/bin/readelf \
> 	OBJDUMP=~/old/bin/objdump OBJCOPY=~/old/bin/objcopy GCC=~/old/bin/gcc
							    ^^ that should be CC
> 

The built kernel (with this patch) does boot till userspace on qemu, so
these old versions aren't producing a completely broken kernel.