On Tue, Jan 26, 2021 at 6:28 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > On Tue, Jan 26, 2021 at 06:16:01AM +0900, Masahiro Yamada wrote: > > On Tue, Jan 26, 2021 at 5:42 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > > > > When building out-of-tree kernel modules, the build system doesn't > > > require the GCC version to match the version used to build the original > > > kernel. That's probably [1] fine. > > > > > > In fact, for many distros, the version of GCC used to build the latest > > > kernel doesn't necessarily match the latest released GCC, so a GCC > > > mismatch turns out to be pretty common. And with CONFIG_MODVERSIONS > > > it's probably more common. > > > > > > So a lot of users have come to rely on being able to use a different > > > version of GCC when building OOT modules. > > > > > > But with GCC plugins enabled, that's no longer allowed: > > > > > > cc1: error: incompatible gcc/plugin versions > > > cc1: error: failed to initialize plugin ./scripts/gcc-plugins/structleak_plugin.so > > > > > > That error comes from the plugin's call to > > > plugin_default_version_check(), which strictly enforces the GCC version. > > > The strict check makes sense, because there's nothing to prevent the GCC > > > plugin ABI from changing -- and it often does. > > > > > > But failing the build isn't necessary. For most plugins, OOT modules > > > will otherwise work just fine without the plugin instrumentation. > > > > > > When a GCC version mismatch is detected, print a warning and disable the > > > plugin. The only exception is the RANDSTRUCT plugin which needs all > > > code to see the same struct layouts. In that case print an error. > > > > > > [1] Ignoring, for the moment, that the kernel now has > > > toolchain-dependent kconfig options, which can silently disable > > > features and cause havoc when compiler versions differ, or even when > > > certain libraries are missing. This is a separate problem which > > > also needs to be addressed. > > > > > > Reported-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx> > > > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > > > --- > > > > > > We are based on the assumption that we use the same > > compiler for in-tree and out-of-tree. > > Sorry, but that assumption isn't based in reality. And it's not > enforced. > > > If people use a different compiler, they must be > > prepared for any possible problem. > > > > Using different compiler flags for in-tree and out-of-tree > > is even more dangerous. > > > > For example, CONFIG_GCC_PLUGIN_RANDSTRUCT is enabled > > for in-tree build, and then disabled for out-of-tree modules, > > the struct layout will mismatch, won't it? > > If you read the patch you'll notice that it handles that case, when it's > caused by GCC mismatch. > > However, as alluded to in the [1] footnote, it doesn't handle the case > where the OOT build system doesn't have gcc-plugin-devel installed. > Then CONFIG_GCC_PLUGIN_RANDSTRUCT gets silently disabled and the build > succeeds! That happens even without a GCC mismatch. Ah, sorry. I responded too early before reading the patch fully. But, I do not like to make RANDSTRUCT a special case. I'd rather want to stop building for any plugin. > > This patch is ugly, and not doing the right thing. > > Maybe, but I doubt the solution is to make assumptions. > > -- > Josh > -- Best Regards Masahiro Yamada
