On Tue, Feb 19, 2019 at 2:43 PM Nick Desaulniers <ndesaulni...@google.com> wrote: > > + Evgenii, Kostya for KASAN > > On Tue, Feb 19, 2019 at 2:17 PM Qian Cai <c...@lca.pw> wrote: > > > > On Tue, 2019-02-19 at 22:49 +0100, Arnd Bergmann wrote: > > > Building an arm64 allmodconfig kernel with clang results in over 140 > > > warnings > > > about overly large stack frames, the worst ones being: > > > > > > drivers/gpu/drm/panel/panel-sitronix-st7789v.c:196:12: error: stack frame > > > size > > > of 20224 bytes in function 'st7789v_prepare' > > > drivers/video/fbdev/omap2/omapfb/displays/panel-tpo-td028ttec1.c:196:12: > > > error: stack frame size of 13120 bytes in function > > > 'td028ttec1_panel_enable' > > > drivers/usb/host/max3421-hcd.c:1395:1: error: stack frame size of 10048 > > > bytes > > > in function 'max3421_spi_thread' > > > drivers/net/wan/slic_ds26522.c:209:12: error: stack frame size of 9664 > > > bytes > > > in function 'slic_ds26522_probe' > > > drivers/crypto/ccp/ccp-ops.c:2434:5: error: stack frame size of 8832 > > > bytes in > > > function 'ccp_run_cmd' > > > drivers/media/dvb-frontends/stv0367.c:1005:12: error: stack frame size of > > > 7840 > > > bytes in function 'stv0367ter_algo' > > > > > > None of these happen with gcc today, and almost all of these are the > > > result > > > of a single known bug in llvm. Hopefully it will eventually get fixed > > > with > > > the > > > clang-9 release.
I am not confident we can fix this in clang. The difference between gcc and clang, AFAICT, is not in the asan instrumentation, but in inining. Looking at the reproducer from https://bugs.llvm.org/show_bug.cgi?id=38809#c4, if I change ltv350qv_write_reg to always inline, gcc also produces a huge 10K stack frame, and making it noinline fixes the stack frame for both gcc and clang. > > Would it be better to disable outright if CC_IS_CLANG, then go back > and adjust it once we know explicitly which version it lands in? > (Maybe I'm being too pessimistic about when it may be fixed). > > > > > > > In the meantime, the best idea I have is to turn off asan-stack for > > > clang-8 > > > and earlier, so we can produce a kernel that is safe to run. > > > > > > I have posted three patches that address the frame overflow warnings that > > > are > > > not addressed by turning off asan-stack, so in combination with this > > > change, > > > we get much closer to a clean allmodconfig build, which in turn is > > > necessary > > > to do meaningful build regression testing. > > > > Well, I am using clang 8.0 on arm64 and running the kernel just fine for a > > few > > weeks now and never trigger a single stack overflow (THREAD_SHIFT = 15) > > because > > I never use any of those drivers you mentioned above. I don't think it is a > > good > > idea to blankly remove the testing coverage here and affect people don't > > use all > > those offensive functions at all. > > Thanks for the patch, Arnd! Hopefully we can fix that up in Clang > soon. Qian, I guess the alternative would be to add `-mllvm > -asan-stack=0` on potentially up to 140 Makefiles? > > -- > Thanks, > ~Nick Desaulniers
