Commit 9618bde4 authored Oct 05, 2020 by Yonghong Song Committed by Alexei Starovoitov Oct 06, 2020

samples/bpf: Change Makefile to cope with latest llvm

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@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20201006043427.1891742-1-yhs@fb.com

parent 8cee9107

samples/bpf/Makefile

+10 −1

Original line number	Diff line number	Diff line
		@@ -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

		@@ -303,6 +305,11 @@ $(obj)/hbm_edt_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
		# asm/sysreg.h - inline assembly used by it is incompatible with llvm.
		# But, there is no easy way to fix it, so just exclude it since it is
		# useless for BPF samples.
		# below we use long chain of commands, clang \| opt \| llvm-dis \| llc,
		# to generate final object file. 'clang' compiles the source into IR
		# with native target, e.g., x64, arm64, etc. 'opt' does bpf CORE IR builtin
		# processing (llvm12) and IR optimizations. 'llvm-dis' converts
		# 'opt' output to IR, and finally 'llc' generates bpf byte code.
		$(obj)/%.o: $(src)/%.c
		@echo " CLANG-bpf " $@
		$(Q)$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(BPF_EXTRA_CFLAGS) \
		@@ -314,7 +321,9 @@ $(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 $@
		ifeq ($(DWARF2BTF),y)
		$(BTF_PAHOLE) -J $@
		endif

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