Re: linker script /arch/arm64/kernel/vmlinux.lds build error

From: Sami Tolvanen <samitolvanen@google.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "Mohan Rao .vanimina" <mailtoc.mohanrao@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	 linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Kees Cook <keescook@chromium.org>,
	 Nathan Chancellor <nathan@kernel.org>,
	Will Deacon <will@kernel.org>
Subject: Re: linker script /arch/arm64/kernel/vmlinux.lds build error
Date: Tue, 20 Sep 2022 08:06:12 -0700	[thread overview]
Message-ID: <CABCJKufrRCb84fafhsR8_fftBLv0_pvufL_ZZieUSTJfhdT+fw@mail.gmail.com> (raw)
In-Reply-To: <YymwCxtUNclGDxyZ@FVFF77S0Q05N>

On Tue, Sep 20, 2022 at 5:20 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Thu, Sep 15, 2022 at 09:10:45PM +0530, Mohan Rao .vanimina wrote:
> > Thanks for the info. Sorry for this delay in the response.
> > As suggested I have modified the PAGE SIZE granularity from
> > ARM64_4K_PAGES to ARM64_64K_PAGES in the applicable config file but
> > still the build is failing with the same linker error.
> > Kindly note that the build compilation is successful for the case of
> > when configuring PAGE size to ARM64_16K_PAGES. Though there is some
> > issue that the device is crashing at bootup itself, compilation was
> > getting through without any issues for ARM64_16K_PAGES.
> > I wonder why the ARM64_64K_PAGES scenario is failing, there must be
> > some sanity checks at the build integration(kernel build tests) that
> > would have been caught this linker build issue if indeed it's really a
> > bug or failed due to some in-complete change.
>
> Since you're using LTO, your config is clearly divergent from defconfig; if you
> could share your config it would help a lot.
>
> I suspect what's happening here is exactly what the linker error describes:
> you're building a config without a PMD level (e.g. 64K pages with 42-bit VAs),
> but there's some code that blindly assumes the PMD level exists and depends on
> the non-existent PMD_SIZE definition.
>
> I suspect you've enabled CFI_CLANG, and the TEXT_CFI_JT section in the linker
> script, which would explain the problem.
>
> I don't understand why that's aligned to anything more than an instruction
> boundary to begin with. I don't see why it would need to be aligned to 2MB with
> 4K pages, nor with 512MB with 64K pages.
>
> Sami, Kees, Nathan, any idea on where this alignment came from?
>
> Will had mentioned this in passing before as bloating the kernel Image size,
> but I hadn't realsied this also caused a build failure until now.

This was a leftover from an old x86 series, which was included here by
mistake. Will also asked me about this a couple of weeks ago, I think,
and said he'd send a patch to remove it.

Sami

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