Linux: -Wparentheses-equality in arch/arm/lib/uaccess_with_memcpy.c

[nickdesaulniers]

from linaro tcwg ci:

00:00:35 arch/arm/lib/uaccess_with_memcpy.c:93:45: warning: equality comparison with extraneous parentheses [-Wparentheses-equality]
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
00:00:35 arch/arm/lib/uaccess_with_memcpy.c:93:45: note: remove extraneous parentheses around the comparison to silence this warning
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35      ~                                      ^              ~
00:00:35 arch/arm/lib/uaccess_with_memcpy.c:93:45: note: use '=' to turn this equality comparison into an assignment
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35                                             ^~
00:00:35                                             =
00:00:35 arch/arm/lib/uaccess_with_memcpy.c:166:45: warning: equality comparison with extraneous parentheses [-Wparentheses-equality]
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
00:00:35 arch/arm/lib/uaccess_with_memcpy.c:166:45: note: remove extraneous parentheses around the comparison to silence this warning
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35      ~                                      ^              ~
00:00:35 arch/arm/lib/uaccess_with_memcpy.c:166:45: note: use '=' to turn this equality comparison into an assignment
00:00:35  if ((((current_thread_info()->addr_limit)) == (0x00000000))) {
00:00:35                                             ^~
00:00:35                                             =
00:00:35 2 warnings generated.

[nathanchance]

So all of these warnings that got filed appear to be from preprocessed sources (this is expanded from uaccess_kernel()). How do I reproduce this and how should it be fixed?

Relevant bits:

https://elixir.bootlin.com/linux/v5.1-rc3/source/arch/arm/lib/uaccess_with_memcpy.c#L93

https://elixir.bootlin.com/linux/v5.1-rc3/source/include/linux/uaccess.h#L9

https://elixir.bootlin.com/linux/v5.1-rc3/source/arch/arm/include/asm/uaccess.h#L66

https://elixir.bootlin.com/linux/v5.1-rc3/source/arch/arm/include/asm/uaccess.h#L82

[nickdesaulniers]

I was using the report from:
https://ci.linaro.org/job/tcwg_kernel-bisect-llvm-master-arm-mainline-allmodconfig/15/
which by the name alone seems to imply arm (32b) allmodconfig.

If these are not reproducible, feel free to close.

[nathanchance]

Ah, I remember why this happens. It's a ccache bug, as we ran into this with our own CI:

ccache no longer passes preprocessor options like -D and -I to the compiler when compiling preprocessed output. This fixes warnings emitted by Clang.

https://ccache.dev/releasenotes.html#_ccache_3_2

https://github.com/ClangBuiltLinux/continuous-integration/commit/4f048dbbd20f07ac793535fc15f90ce38ffa9a8f

https://travis-ci.com/ClangBuiltLinux/continuous-integration/builds/89768767 vs. https://travis-ci.com/ClangBuiltLinux/continuous-integration/builds/89763935

Ideally, Linaro should fix this by updating their ccache binary. I don't know how feasible that is but there is nothing for us to fix here so closing.

[nickdesaulniers]

yep, that will do it, thanks for recalling that this issue has been seen before!

[maxim-kuvyrkov]

Linaro TCWG uses ubuntu:xenial docker containers for these builds, which have old enough ccache 3.2.4.
docker run --rm --entrypoint /usr/bin/ccache linaro/ci-amd64-tcwg-build-ubuntu:xenial --version ccache version 3.2.4

[nathanchance]

Odd. Maybe it wasn't fully fixed until a later version. All I know is it is ccache related because we upgraded to the latest between builds and that resolved the slew of warnings.

[maxim-kuvyrkov]

What ccache version works for you?

[nathanchance]

I know that ccache 3.3.4 worked when we were using Debian stretch as our base.

[maxim-kuvyrkov]

I've switched Linaro TCWG kernel CI to use ubuntu:bionic with ccache 3.4.1. Let's see how it'll go.