On Wed, Sep 08, 2021 at 12:14:19AM +0200, Marco Elver wrote: > On Tue, Sep 07, 2021 at 01:30PM -0700, Nick Desaulniers wrote: > > On Tue, Sep 7, 2021 at 12:16 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > [...] > > > I'm not going to revert that change. I probably will have to limit it > > > (by making that WERROR option depend on certain expectations), but > > > basically any maintainer who has code that causes warnings should > > > expect that they will have to fix those warnings. > > > > I'm not 100% against it; I think it could land in a more useful > > variation. But it would be good to discuss that on-list, and give it > > time to soak. This is a conversation we should be having with CI > > maintainers IMO, and folks that maintain the build infra, at least. > > I'm happy to kick off that discussion with this RFC. > > Here's a datapoint: I had to disable CONFIG_WERROR on a bunch of syzbot > instances which started failing because of -Werror [1], because syzbot's > time is better spent on fuzzing, and having the odd warning in some > subsystem penalize fuzzing of the entire kernel is not appropriate. > > [1] https://github.com/google/syzkaller/commit/e096c0a2a414e487412c9669426780ce5acdde9d > > Getting the kernel built is a hard requirement for any sort of runtime > testing. Once the kernel is built, runtime testing of various subsystems > can proceed in parallel. A single warning in some odd subsystem > penalizing the _entire_ kernel's testing progress is inappropriate. The > severity of a use-after-free bug found by runtime testing is orders of > magnitude more severe than some "unused variable" warning. Now such a > warning would delay finding bugs at runtime on many CI systems that > haven't yet disabled the warning. > > I'm predicting most distributions and runtime-focused CIs will disable > the warning. > > I have formulated this in the form of a patch below, that might move > this new Kconfig option towards its appropriate usecases by default. > > The intent is not to dispute the usefulness of -Werror, but select the > appropriate usecases by default, limiting friction for all those who can > do little more than say CONFIG_WERROR=n. > > Thanks, > -- Marco > > ------ >8 ------ > > From: Marco Elver <elver@xxxxxxxxxx> > Date: Tue, 7 Sep 2021 23:12:08 +0200 > Subject: [PATCH] kbuild: Only default to -Werror if COMPILE_TEST > > The cross-product of the kernel's supported toolchains, architectures, > and configuration options is large. So large, that it's generally > accepted to be infeasible to enumerate and build+test them all > (many compile-testers rely on randomly generated configs). > > Without the possibility to enumerate all possible combinations of > toolchains, architectures, and configuration options, it is inevitable > that compiler warnings in this space exist. > > With -Werror, this means that an innumerable set of kernels are now > broken, yet had been perfectly usable before (confused compilers, code > with warnings unused, or luck). > > Distributors will necessarily pick a point in the toolchain X arch X > config space, and if unlucky, will have a broken build. Granted, those > will likely disable CONFIG_WERROR and move on. > > The kernel's default configuration is unlikely to be suitable for all > users, but it's inappropriate to force many users to set CONFIG_WERROR=n. > > This also holds for CI systems which are focused on runtime testing, > where the odd warning in some subsystem will disrupt testing of the rest > of the kernel. Many of those runtime-focused CI systems run tests or > fuzz the kernel using runtime debugging tools. Runtime testing of > different subsystems can proceed in parallel, and potentially uncover > serious bugs; halting runtime testing of the entire kernel because of > the odd warning (now error) in a subsystem or driver is simply > inappropriate. > > Therefore, runtime-focused CI systems will likely choose CONFIG_WERROR=n > as well. > > The appropriate usecase for -Werror is therefore compile-test focused > builds (often done by developers or CI systems). > > Reflect this in the Kconfig option by making the default value of WERROR > match COMPILE_TEST. > > Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> > --- > init/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/init/Kconfig b/init/Kconfig > index 8cb97f141b70..11f8a845f259 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -139,7 +139,7 @@ config COMPILE_TEST > > config WERROR > bool "Compile the kernel with warnings as errors" > - default y > + default COMPILE_TEST > help > A kernel build should not cause any compiler warnings, and this > enables the '-Werror' flag to enforce that rule by default. > -- > 2.33.0.153.gba50c8fa24-goog
