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://bugs.llvm.org/ 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://reviews.llvm.org/D87153 > 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 $@ I keep forgetting exact details of why we do this native clang + llc pipeline instead of just doing `clang -target bpf`? Is it still relevant and necessary, or we can just simplify it now? > ifeq ($(DWARF2BTF),y) > $(BTF_PAHOLE) -J $@ > endif > -- > 2.24.1 >
