Re: [PATCH 00/12] ARM: use adr_l/ldr_l macros for PC-relative references

From: Nicolas Pitre <nico@fluxnic.net>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	Russell King <linux@armlinux.org.uk>,
	Linus Walleij <linus.walleij@linaro.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Stefan Agner <stefan@agner.ch>, Peter Smith <Peter.Smith@arm.com>,
	Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH 00/12] ARM: use adr_l/ldr_l macros for PC-relative references
Date: Mon, 14 Sep 2020 10:06:11 -0400 (EDT)	[thread overview]
Message-ID: <nycvar.YSQ.7.78.906.2009141003360.4095746@knanqh.ubzr> (raw)
In-Reply-To: <20200914095706.3985-1-ardb@kernel.org>

On Mon, 14 Sep 2020, Ard Biesheuvel wrote:

> This is a respin of the adr_l/ldr_l code I wrote some years ago in the
> context of my KASLR proof of concept for 32-bit ARM.
> 
> A new use case came up, in the form of Clang, which does not implement
> the 'adrl' pseudo-instruction in its assembler, and so for PC-relative
> references that don't fit into a ARM adr instruction, we need something
> else. Patch #2 addresses an actual Clang build issue of this nature, by
> replacing an occurrence of adrl with adr_l.
> 
> I have included my existing cleanup patches that were built on top of the
> adr_l macro, which replace several occurrences of open coded arithmetic to
> calculate runtime addresses based on link time virtual addresses stored
> in literals.
> 
> Note that all of these patches with the exception of #2 were reviewed or
> acked by Nico before, but given that this was a while ago (and the fact

Certainly it must have been, as I didn't remember much of it.

> that neither of us work for Linaro anymore), I have dropped these. Note
> that only patch #1 deviates significantly from the last version that I
> sent out, the remaining ones were just freshened up (and their commit
> logs slightly expanded).

Reviewed-by: Nicolas Pitre <nico@fluxnic.net>

> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Nicolas Pitre <nico@fluxnic.net>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Stefan Agner <stefan@agner.ch>
> Cc: Peter Smith <Peter.Smith@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Will Deacon <will@kernel.org>
> 
> Ard Biesheuvel (12):
>   ARM: assembler: introduce adr_l, ldr_l and str_l macros
>   ARM: efistub: replace adrl pseudo-op with adr_l macro invocation
>   ARM: module: add support for place relative relocations
>   ARM: head-common.S: use PC-relative insn sequence for __proc_info
>   ARM: head-common.S: use PC-relative insn sequence for idmap creation
>   ARM: head.S: use PC-relative insn sequence for secondary_data
>   ARM: kernel: use relative references for UP/SMP alternatives
>   ARM: head: use PC-relative insn sequence for __smp_alt
>   ARM: sleep.S: use PC-relative insn sequence for
>     sleep_save_sp/mpidr_hash
>   ARM: head.S: use PC-relative insn sequences for __fixup_pv_table
>   ARM: head.S: use PC relative insn sequence to calculate PHYS_OFFSET
>   ARM: kvm: replace open coded VA->PA calculations with adr_l call
> 
>  arch/arm/boot/compressed/head.S  | 18 +---
>  arch/arm/include/asm/assembler.h | 88 ++++++++++++++++++-
>  arch/arm/include/asm/elf.h       |  5 ++
>  arch/arm/include/asm/processor.h |  2 +-
>  arch/arm/kernel/head-common.S    | 22 ++---
>  arch/arm/kernel/head.S           | 90 +++++---------------
>  arch/arm/kernel/hyp-stub.S       | 27 +++---
>  arch/arm/kernel/module.c         | 20 ++++-
>  arch/arm/kernel/sleep.S          | 19 ++---
>  9 files changed, 159 insertions(+), 132 deletions(-)
> 
> -- 
> 2.17.1
> 
> 