On Fri, Oct 2, 2020 at 10:16 PM Yonghong Song <yhs@xxxxxx> wrote: > > > > On 10/2/20 9:22 PM, Andrii Nakryiko wrote: > > On Fri, Oct 2, 2020 at 7:19 PM Yonghong Song <yhs@xxxxxx> wrote: > >> > >> With latest llvm trunk, bpf programs under samples/bpf > >> directory, if using CORE, may experience the following > >> errors: > >> > >> LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index > >> PLEASE submit a bug report to https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=BwTAvhipPl-Az_WaiJDbqU8yl__NvG8W4HmCqWqHdqg&e= and include the crash backtrace. > >> Stack dump: > >> 0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o > >> 1. Running pass 'Function Pass Manager' on module '<stdin>'. > >> 2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1' > >> #0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) > >> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c) > >> ... > >> #7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e) > >> #8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*) > >> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5) > >> #9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*, > >> unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8) > >> ... > >> Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o > >> > >> The reason is due to llvm change https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D87153&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=fo_LvXqHJx_m0m0pJJiDdOUcOzVXm2_iYoxPhpqpzng&e= > >> where the CORE relocation global generation is moved from the beginning > >> of target dependent optimization (llc) to the beginning > >> of target independent optimization (opt). > >> > >> Since samples/bpf programs did not use vmlinux.h and its clang compilation > >> uses native architecture, we need to adjust arch triple at opt level > >> to do CORE relocation global generation properly. Otherwise, the above > >> error will appear. > >> > >> This patch fixed the issue by introduce opt and llvm-dis to compilation chain, > >> which will do proper CORE relocation global generation as well as O2 level > >> optimization. Tested with llvm10, llvm11 and trunk/llvm12. > >> > >> Signed-off-by: Yonghong Song <yhs@xxxxxx> > >> --- > >> samples/bpf/Makefile | 6 +++++- > >> 1 file changed, 5 insertions(+), 1 deletion(-) > >> > >> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile > >> index 4f1ed0e3cf9f..79c5fdea63d2 100644 > >> --- a/samples/bpf/Makefile > >> +++ b/samples/bpf/Makefile > >> @@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread > >> # make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang > >> LLC ?= llc > >> CLANG ?= clang > >> +OPT ?= opt > >> +LLVM_DIS ?= llvm-dis > >> LLVM_OBJCOPY ?= llvm-objcopy > >> BTF_PAHOLE ?= pahole > >> > >> @@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c > >> -Wno-address-of-packed-member -Wno-tautological-compare \ > >> -Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \ > >> -I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \ > >> - -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@ > >> + -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \ > >> + $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \ > >> + $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@ This is an extremely unusual set of steps, and might be worthwhile to leave a comment explaining what's going on, so that I or someone else doesn't ask the same question few months later :) At any rate, this fixes the issue, so: Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > > > > I keep forgetting exact details of why we do this native clang + llc > > pipeline instead of just doing `clang -target bpf`? Is it still > > samples/bpf programs did not use vmlinux.h. they directly use > kernel-devel headers, hence they need to first compile with native arch > for clang but later change target arch to bpf to generate final byte code. > They cannot just do 'clang -target bpf' without vmlinux.h. Ok, right, thanks for explanation. I wonder if this "native" clang + llc pass will also help with vmlinux.h on 32-bit architectures (though with my recent patches that shouldn't be necessary, so this is more of a curiosity, rather than the need). > > But changing to use vmlinux.h is a much bigger project and I merely > want to make it just work so people won't make/compile samples/bpf > and get compilation errors. Right, of course. > > > relevant and necessary, or we can just simplify it now? > > > >> ifeq ($(DWARF2BTF),y) > >> $(BTF_PAHOLE) -J $@ > >> endif > >> -- > >> 2.24.1 > >>
