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

[Nick Desaulniers]

On Mon, Sep 14, 2020 at 2:57 AM Ard Biesheuvel <ardb at kernel.org> 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
> 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).

Tested-by: Nick Desaulniers <ndesaulniers at google.com>

Thanks for the series, Ard.  I was able to compile and boot the
following with this series (and the fixup to 01/12 applied):

$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make defconfig
$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 defconfig
$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 aspeed_g5_defconfig
$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 multi_v5_defconfig

(So ARM v7/GCC, ARM v5,6,7/LLVM).  (Technically, the v6 is not
booting, but it's not related to this series and fails to boot without
the series as well.  Our CI on -next is red for an unrelated issue
which is masking the regression).

I was also able to build+boot the defconfig with v5 and v7 with some
configs disabled and a few hacks with LLVM_IAS=1.  This series allowed
me to get further in the build/testing, and I have a few new bugs to
go chase.  If anyone's interested:
https://github.com/ClangBuiltLinux/linux/issues/1154
https://github.com/ClangBuiltLinux/linux/issues/1155
so we're still a handful of bugs away from LLVM_IAS=1 with ARCH=arm,
but we're steadily chipping away at it, and this series is a big help.
Lest it look like there's only kernel fixes in this area, Jian's
https://reviews.llvm.org/D69411 recently was a big help, specifically
for ARCH=arm LLVM_IAS=1.
-- 
Thanks,
~Nick Desaulniers