From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Ellerman Date: Mon, 21 Jun 2021 09:46:03 +0000 Subject: Re: arch/powerpc/kvm/book3s_hv_nested.c:264:6: error: stack frame size of 2304 bytes in function 'kv Message-Id: <87im273604.fsf@mpe.ellerman.id.au> List-Id: References: <202104031853.vDT0Qjqj-lkp@intel.com> <1624232938.d90brlmh3p.astroid@bobo.none> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable To: Nathan Chancellor , Nicholas Piggin , Arnd Bergmann , kernel test robot Cc: Andrew Morton , clang-built-linux@googlegroups.com, kbuild-all@lists.01.org, Kees Cook , linux-kernel@vger.kernel.org, Linux Memory Management List , linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org Nathan Chancellor writes: > On 6/20/2021 4:59 PM, Nicholas Piggin wrote: >> Excerpts from kernel test robot's message of April 3, 2021 8:47 pm: >>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.= git master >>> head: d93a0d43e3d0ba9e19387be4dae4a8d5b175a8d7 >>> commit: 97e4910232fa1f81e806aa60c25a0450276d99a2 linux/compiler-clang.h= : define HAVE_BUILTIN_BSWAP* >>> date: 3 weeks ago >>> config: powerpc64-randconfig-r006-20210403 (attached as .config) >>> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 0f= e8af94688aa03c01913c2001d6a1a911f42ce6) >>> reproduce (this is a W=3D1 build): >>> wget https://raw.githubusercontent.com/intel/lkp-tests/master/= sbin/make.cross -O ~/bin/make.cross >>> chmod +x ~/bin/make.cross >>> # install powerpc64 cross compiling tool for clang build >>> # apt-get install binutils-powerpc64-linux-gnu >>> # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin= ux.git/commit/?id=97e4910232fa1f81e806aa60c25a0450276d99a2 >>> git remote add linus https://git.kernel.org/pub/scm/linux/kern= el/git/torvalds/linux.git >>> git fetch --no-tags linus master >>> git checkout 97e4910232fa1f81e806aa60c25a0450276d99a2 >>> # save the attached .config to linux build tree >>> COMPILER_INSTALL_PATH=3D$HOME/0day COMPILER=3Dclang make.cross= ARCH=3Dpowerpc64 >>> >>> If you fix the issue, kindly add following tag as appropriate >>> Reported-by: kernel test robot >>> >>> All errors (new ones prefixed by >>): >>> >>>>> arch/powerpc/kvm/book3s_hv_nested.c:264:6: error: stack frame size of= 2304 bytes in function 'kvmhv_enter_nested_guest' [-Werror,-Wframe-larger-= than=3D] >>> long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu) >>> ^ >>> 1 error generated. >>> >>> >>> vim +/kvmhv_enter_nested_guest +264 arch/powerpc/kvm/book3s_hv_nested.c >>=20 >> Not much changed here recently. It's not that big a concern because it's >> only called in the KVM ioctl path, not in any deep IO paths or anything, >> and doesn't recurse. Might be a bit of inlining or stack spilling put it >> over the edge. > > It appears to be the fact that LLVM's PowerPC backend does not emit=20 > efficient byteswap assembly: > > https://github.com/ClangBuiltLinux/linux/issues/1292 > > https://bugs.llvm.org/show_bug.cgi?idI610 > >> powerpc does make it an error though, would be good to avoid that so the >> robot doesn't keep tripping over. > > Marking byteswap_pt_regs as 'noinline_for_stack' drastically reduces the = > stack usage. If that is an acceptable solution, I can send it along=20 > tomorrow. Yeah that should be OK. Can you post the before/after disassembly when you post the patch? It should just be two extra function calls, which shouldn't be enough overhead to be measurable. cheers