On Tue, Jan 26, 2021 at 5:42 AM Josh Poimboeuf <jpoim...@redhat.com> 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 <omosn...@redhat.com> > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > ---
We are based on the assumption that we use the same compiler for in-tree and out-of-tree. 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? This patch is ugly, and not doing the right thing. > scripts/Makefile.gcc-plugins | 19 +++++++++++++++++++ > scripts/Makefile.kcov | 11 +++++++++++ > 2 files changed, 30 insertions(+) > > diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins > index 952e46876329..7227692fba59 100644 > --- a/scripts/Makefile.gcc-plugins > +++ b/scripts/Makefile.gcc-plugins > @@ -51,6 +51,25 @@ export DISABLE_ARM_SSP_PER_TASK_PLUGIN > GCC_PLUGINS_CFLAGS := $(strip $(addprefix > -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) > $(gcc-plugin-cflags-y)) > # The sancov_plugin.so is included via CFLAGS_KCOV, so it is removed here. > GCC_PLUGINS_CFLAGS := $(filter-out %/sancov_plugin.so, $(GCC_PLUGINS_CFLAGS)) > + > +# Out-of-tree module check: If there's a GCC version mismatch, disable > plugins > +# and print a warning. Otherwise the OOT module build will fail due to > +# plugin_default_version_check(). > +ifneq ($(GCC_PLUGINS_CFLAGS),) > + ifneq ($(KBUILD_EXTMOD),) > + ifneq ($(CONFIG_GCC_VERSION), $(shell > $(srctree)/scripts/gcc-version.sh $(HOSTCXX))) > + > + ifdef CONFIG_GCC_PLUGIN_RANDSTRUCT > + $(error error: CONFIG_GCC_PLUGIN_RANDSTRUCT requires > out-of-tree modules to be built using the same GCC version as the kernel.) > + endif > + > + $(warning warning: Disabling GCC plugins for out-of-tree modules > due to GCC version mismatch.) > + $(warning warning: The following plugins have been disabled: > $(gcc-plugin-y)) > + GCC_PLUGINS_CFLAGS := > + endif > + endif > +endif > + > export GCC_PLUGINS_CFLAGS > > # Add the flags to the build! > diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov > index 67e8cfe3474b..63a2bc2aabb2 100644 > --- a/scripts/Makefile.kcov > +++ b/scripts/Makefile.kcov > @@ -3,4 +3,15 @@ kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC) += > -fsanitize-coverage=trace-pc > kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS) += > -fsanitize-coverage=trace-cmp > kcov-flags-$(CONFIG_GCC_PLUGIN_SANCOV) += > -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so > > +# Out-of-tree module check for GCC version mismatch. > +# See the similar check in scripts/Makefile.gcc-plugins > +ifneq ($(CONFIG_GCC_PLUGIN_SANCOV),) > + ifneq ($(KBUILD_EXTMOD),) > + ifneq ($(CONFIG_GCC_VERSION), $(shell > $(srctree)/scripts/gcc-version.sh $(HOSTCXX))) > + $(warning warning: Disabling CONFIG_GCC_PLUGIN_SANCOV for > out-of-tree modules due to GCC version mismatch.) > + kcov-flags-y := $(filter-out %/sancov_plugin.so, $(kcov-flags-y)) > + endif > + endif > +endif > + > export CFLAGS_KCOV := $(kcov-flags-y) > -- > 2.29.2 > -- Best Regards Masahiro Yamada
