On Fri, Sep 21, 2018 at 10:59 AM Nick Desaulniers <ndesaulni...@google.com> wrote: > > On Fri, Sep 21, 2018 at 2:45 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > > > On Fri, Sep 21, 2018 at 11:25 AM, Andrey Ryabinin > > <aryabi...@virtuozzo.com> wrote: > > > On 09/21/2018 04:50 AM, Andy Lutomirski wrote: > > >> This patch seems reasonable, but you emailed the wrong people :) > > >> > > >> On Thu, Sep 20, 2018 at 5:15 PM Jason A. Donenfeld <ja...@zx2c4.com> > > >> wrote: > > >>> > > >>> It turns out that KASAN in general will bloat stack frames in unexpected > > >>> ways, not just KASAN_EXTRA. So, this patch trivially changes that > > >>> default to be associated with KASAN instead of KASAN_EXTRA. > > >>> > > > > > > KASAN_EXTRA bloats stack more than just KASAN, that's why the limit is > > > higher than just for KASAN. > > > If want more details, tead the changelog from commit > > > e7c52b84fb18f08ce49b6067ae6285aca79084a8 > > > > > > If anything causes "stack frame > 2048" warning for KASAN we should at > > > least try to fix it, > > > I mean reduce stack usage. > > > > > > +Nick who is also hitting these warnings on clang/arm64 build. As far > > as I understand the situation there is much worse. > > > > I would be good to understand/fix the worst offenders. But the stack > > size increase with KASAN is a real, inherent thing. So if we live very > > close the edge, we can get people using different compilers and/or > > versions of compilers constantly breaking each other. And clang hits > > this warnings in lots of places today just because the current code > > was tailored to gcc over long period, i.e. allowing more locals where > > gcc happened to handle that better and having fewer locals where gcc > > happened to handle it worse. But for another compiler all these > > assumptions are significantly perturbed. > > > > Nick, do you know what frame size limit eliminates the bulk of > > warnings on clang? Is 3072 a reasonable limit allowing to fix the > > remaining outliners? > > Here's a plot of the distribution from an arm64 clang build with > allyesconfig minus LSE_ATOMICS, BIG_ENDIAN, and GCOV: > https://github.com/ClangBuiltLinux/linux/issues/39#issuecomment-423621655 > > A value of 3072 would ignore 79 out of the 128 instances (62%).
A value of 4614 would ignore 95% of the instances (2 standard deviations of the distribution of current warnings). > > Some values are huge outliers. > > > > > > > >>> Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com> > > >>> --- > > >>> lib/Kconfig.debug | 2 +- > > >>> 1 file changed, 1 insertion(+), 1 deletion(-) > > >>> > > >>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > >>> index 4966c4fbe7f7..39078a080e29 100644 > > >>> --- a/lib/Kconfig.debug > > >>> +++ b/lib/Kconfig.debug > > >>> @@ -222,7 +222,7 @@ config ENABLE_MUST_CHECK > > >>> config FRAME_WARN > > >>> int "Warn for stack frames larger than (needs gcc 4.4)" > > >>> range 0 8192 > > >>> - default 3072 if KASAN_EXTRA > > >>> + default 3072 if KASAN > > >>> default 2048 if GCC_PLUGIN_LATENT_ENTROPY > > >>> default 1280 if (!64BIT && PARISC) > > >>> default 1024 if (!64BIT && !PARISC) > > >>> -- > > >>> 2.19.0 > > > > -- > Thanks, > ~Nick Desaulniers -- Thanks, ~Nick Desaulniers
