linux-kernel - Re: [PATCH] arm64: head: set TEXT

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Message-ID: <obcgfnmgdemf5gtc7gdaj6nzoa2rwxsc6njt4fd2ouwzqj4y7y@ztxwyyoepuud>
Date: Wed, 8 Oct 2025 22:51:16 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        David Heidelberg <david@...t.cz>, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, mark.rutland@....com
Subject: Re: [PATCH] arm64: head: set TEXT_OFFSET to the historical value

On Tue, Oct 07, 2025 at 01:46:08AM +0200, Ard Biesheuvel wrote:
> On Mon, 6 Oct 2025 at 16:01, Will Deacon <will@...nel.org> wrote:
> >
> > [+Ard and Mark]
> >
> > On Mon, Oct 06, 2025 at 01:21:04AM +0300, Dmitry Baryshkov wrote:
> > > From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > >
> > > Historically arm64 kernel contained (almost fixed) value of 0x8000 at
> >
> > 0x8000 or 0x80000?
> >
> > > the TEXT_OFFSET. The commit cfa7ede20f13 ("arm64: set TEXT_OFFSET to 0x0
> > > in preparation for removing it entirely") and then commit 120dc60d0bdb
> > > ("arm64: get rid of TEXT_OFFSET") replaced this field with 0.
> >
> > Given that we made the initial change over five years ago, I'm struggling
> > to see why we should start caring about old broken bootloaders _now_.

Well... because support for these devices wasn't upstreamed and so a
similar patch was being kept in the down-upstream kernel.

> >
> > In fact, I'm far more concerned about changing this to a non-zero value
> > and having more recent bootloaders misbehave.

I see.

> >
> > > This caused no problems so far, because nobody seemed to be playing with
> > > the extremely picky Qualcomm bootloader as used on some of Google Pixel
> > > phones. Current attempting to boot the Linux kernel on those devices
> > > will fail to load on those phones with the following message:
> > >
> > > KernelDecompress failed: Invalid Parameter Kernel TextOffset does not match
> > > Error calling BootPrepareAsync Invalid Parameter
> > >
> > > Since the kernel ignores the field, set it to the expected value of
> > > 0x8000, unbreaking boot of upstream kernels on Qualcomm devices.
> >
> > (same typo)
> >
> 
> Just setting the header field and not updating the base address also
> means that the boot breaks without CONFIG_RELOCATABLE, and you will
> get a warning in the kernel log about the load address not being
> aligned to 2 MiB.
> 
> So I don't think this is the right solution.

Since most of the people build the kernel with CONFIG_RELOCATABLE, would
it be better to set it to 0x80000 for relocatable kernels and to 0
otherwise?

> 
> If this is really something that needs to be fixed upstream, we should
> just bring back TEXT_OFFSET in its entirety, but I'm not convinced
> that this is really justified here. As a workaround, you could just
> add 2 MiB - 0x80000 bytes of padding at the start of the image, and
> add your own header (as Will alludes to as well)

Does it mean building a device specific kernel? Or just packing
everything while building the Android boot image?

-- 
With best wishes
Dmitry