Hi Arnd, On Fri, Jun 17, 2022 at 05:08:53PM +0200, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > > The introduction of CONFIG_GCC_PLUGIN_LATENT_ENTROPY raised the > warning limit for 32-bit architectures to a much higher value in > 2016. Initially this had no effect for Arm machines as their kernels > tend to be cross-compiled, and the feature detection for the plugin did > not work with common cross compilers. > > I could not find the original regression report that led to the warning > limit getting raised, but I have been unable to reproduce this with gcc-12 > and linux-5.18 -- all frame sizes appear to be be below the normal 1024 > byte limit on at least arm32 and i386. > > However, the KASAN feature introduced later on does raise the frame size > of a number of functions above the warning limit, in almost all cases to > somewhere below 1280 bytes. The effect is that an arm allmodconfig build > produces no warnings because of the check for the latent entropy plugin, > but a normal KASAN based build with gcc does produce build warnings or > failures when CONFIG_WERROR is set. > > The 1280 byte limit is an arbitrary choice here, as it disables almost > all warnings but leaves a few outliers that are probably better addressed > with code changes. There are a number of functions that are just below the > normal 1024 byte limit at the moment, and an extra 256 bytes for those > is within the expectation, but more than that is probably an indication > of a bad design or a real bug. > > Cc: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: linux-kbuild@xxxxxxxxxxxxxxx > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- > lib/Kconfig.debug | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 3da5f9acb966..8a3afd837e99 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -387,9 +387,9 @@ endif # DEBUG_INFO > config FRAME_WARN > int "Warn for stack frames larger than" > range 0 8192 > - default 2048 if GCC_PLUGIN_LATENT_ENTROPY > default 2048 if PARISC > default 1536 if (!64BIT && XTENSA) > + default 1280 if (!64BIT && KASAN_STACK) For what it's worth, if this was changed to just KASAN, this would improve the situation for clang and ARCH=arm allmodconfig as well. It leaves just two -Wframe-larger-than warnings in drivers/gpu/drm/amd/display, which can be worked around with a kernel side change: https://github.com/ClangBuiltLinux/linux/issues/1455#issuecomment-995337569 Cheers, Nathan
