On Sat, Sep 22, 2018 at 4:56 PM, Arnd Bergmann <a...@arndb.de> 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? > > I do not consider 3072 a reasonable limit at all. For gcc, we managed to fix > or > work around all the bugs that caused excessive stack usage. In almost all > cases there was something seriously wrong with code generation. I added > the KASAN_EXTRA option for the one thing that added an inherent significant > overhead to the stack usage. > > llvm apparently has a similar bug to what we fixed in gcc. I created a > reduced test case for one of the file at: > https://bugs.llvm.org/show_bug.cgi?id=38809 > > Unfortunately, nobody has commented on that so far, but in the > meantime I think the best workaround would be to disable asan-stack > entirely when building with clang, and moving it to KASAN_EXTRA > there, like we did with the scope check on gcc.
Good point. I CCed more people on https://bugs.llvm.org/show_bug.cgi?id=38809
