[PATCH] log: Allow LOG_DEBUG to always enable log output

[Simon Glass]

Hi Tom,

On Wed, 5 Aug 2020 at 12:37, Tom Rini <trini at konsulko.com> wrote:
>
> On Wed, Aug 05, 2020 at 08:31:55PM +0200, Heinrich Schuchardt wrote:
> > On 05.08.20 14:56, Tom Rini wrote:
> > > On Wed, Aug 05, 2020 at 02:54:05PM +0200, Heinrich Schuchardt wrote:
> > >> On 05.08.20 14:18, Tom Rini wrote:
> > >>> On Sun, Jul 26, 2020 at 08:27:35PM -0600, Simon Glass wrote:
> > >>>
> > >>>> At present if CONFIG_LOG enabled, putting LOG_DEBUG at the top of a file
> > >>>> (before log.h inclusion) causes _log() to be executed for every log()
> > >>>> call, regardless of the build- or run-time logging level.
> > >>>>
> > >>>> However there is no guarantee that the log record will actually be
> > >>>> displayed. If the current log level is lower than LOGL_DEBUG then it will
> > >>>> not be.
> > >>>>
> > >>>> Add a way to signal that the log record should always be displayed and
> > >>>> update log_passes_filters() to handle this.
> > >>>>
> > >>>> Signed-off-by: Simon Glass <sjg at chromium.org>
> > >>>
> > >>> This exposes an underlying problem with LOG and clang I believe:
> > >>> https://gitlab.denx.de/u-boot/u-boot/-/jobs/135789
> > >>>
> > >>
> > >> include/log.h:147:44: note: expanded from macro 'log'
> > >>         if (CONFIG_IS_ENABLED(LOG) && (_LOG_DEBUG || _l <=
> > >> _LOG_MAX_LEVEL)) \
> > >>                                                   ^
> > >> drivers/misc/p2sb_emul.c:197:10: error: converting the enum constant to
> > >> a boolean [-Werror,-Wint-in-bool-context]
> > >>
> > >> This seems to be a Clang bug. _LOG_DEBUG is not an enum:
> > >>
> > >> #if CONFIG_IS_ENABLED(LOG)
> > >> #ifdef LOG_DEBUG
> > >> #define _LOG_DEBUG      1
> > >> #else
> > >> #define _LOG_DEBUG      0
> > >> #endif
> > >>
> > >> So there seems to be a bug in the Clang you used.
> > >>
> > >> Compiling with clang on Debian Bullseye does not show the problem:
> > >>
> > >> make HOSTCC=clang sandbox_defconfig
> > >> make HOSTCC=clang CC=clang -j8
> > >>
> > >> clang version 9.0.1-13
> > >> LLVM version 9.0.1
> > >>
> > >> Which Clang version did you use?
> > >>
> > >> This is the change that added the test:
> > >> https://reviews.llvm.org/D63082
> > >>
> > >> -Wint-in-bool-context seems to be new in Clang 10.
> > >>
> > >> All over the U-Boot code we assume that a non-zero integer is true. Do
> > >> we really want to enable -Wint-in-bool-context?
> > >
> > > I'm using the official Clang 10 stable builds.
> > >
> >
> > Do you really want to forbid using integers as booleans
> > (-Wint-in-bool-context)?
>
> So, interesting.  The Linux kernel isn't disabling this warning.  It's
> mentioned in two commits, one of which is "clang found a bug here", of
> which this is not the case.  The other is more like ours:
> commit 968e5170939662341242812b9c82ef51cf140a33
> Author: Nathan Chancellor <natechancellor at gmail.com>
> Date:   Thu Sep 26 09:22:59 2019 -0700
>
>     tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro
>
>     After r372664 in clang, the IF_ASSIGN macro causes a couple hundred
>     warnings along the lines of:
>
>     kernel/trace/trace_output.c:1331:2: warning: converting the enum
>     constant to a boolean [-Wint-in-bool-context]
>     kernel/trace/trace.h:409:3: note: expanded from macro
>     'trace_assign_type'
>                     IF_ASSIGN(var, ent, struct ftrace_graph_ret_entry,
>                     ^
>     kernel/trace/trace.h:371:14: note: expanded from macro 'IF_ASSIGN'
>                     WARN_ON(id && (entry)->type != id);     \
>                                ^
>     264 warnings generated.
>
>     This warning can catch issues with constructs like:
>
>         if (state == A || B)
>
>     where the developer really meant:
>
>         if (state == A || state == B)
>
>     This is currently the only occurrence of the warning in the kernel
>     tree across defconfig, allyesconfig, allmodconfig for arm32, arm64,
>     and x86_64. Add the implicit '!= 0' to the WARN_ON statement to fix
>     the warnings and find potential issues in the future.
>
>     Link: https://github.com/llvm/llvm-project/commit/28b38c277a2941e9e891b2db30652cfd962f070b
>     Link: https://github.com/ClangBuiltLinux/linux/issues/686
>     Link: http://lkml.kernel.org/r/20190926162258.466321-1-natechancellor@gmail.com
>
>     Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>
>     Signed-off-by: Nathan Chancellor <natechancellor at gmail.com>
>     Signed-off-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
>
> Which is like our case, and reworking the test to be explicit.  I lean
> towards that.

Oh dear I really want to vote against that.

if (x)

should allow C to consider x to be a boolean. I am hitting this in
Zephyr and feels like it is undoing a long-standing C feature, with
major disruption, for no benefit I can detect.

Hopefully I am misunderstanding what -Wint-in-bool-context means, and
it just applies to enums?

Regards,
Simon