tools/bpftool: Fix cross-build

mainline inclusion
from mainline-5.14-rc1
commit 0779890f
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0779890fed7817725f399d6ec85730e08ebfdeee

-------------------------------------------------

When the bootstrap and final bpftool have different architectures, we
need to build two distinct disasm.o objects. Add a recipe for the
bootstrap disasm.o.

After commit d510296d ("bpftool: Use syscall/loader program in
"prog load" and "gen skeleton" command.") cross-building bpftool didn't
work anymore, because the bootstrap bpftool was linked using objects
from different architectures:

  $ make O=/tmp/bpftool ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/bpf/bpftool/ V=1
  [...]
  aarch64-linux-gnu-gcc ... -c -MMD -o /tmp/bpftool/disasm.o /home/z/src/linux/kernel/bpf/disasm.c
  gcc ... -c -MMD -o /tmp/bpftool//bootstrap/main.o main.c
  gcc ... -o /tmp/bpftool//bootstrap/bpftool /tmp/bpftool//bootstrap/main.o ... /tmp/bpftool/disasm.o
  /usr/bin/ld: /tmp/bpftool/disasm.o: Relocations in generic ELF (EM: 183)
  /usr/bin/ld: /tmp/bpftool/disasm.o: Relocations in generic ELF (EM: 183)
  /usr/bin/ld: /tmp/bpftool/disasm.o: Relocations in generic ELF (EM: 183)
  /usr/bin/ld: /tmp/bpftool/disasm.o: error adding symbols: file in wrong format
  collect2: error: ld returned 1 exit status
  [...]

The final bpftool was built for e.g. arm64, while the bootstrap bpftool,
executed on the host, was built for x86. The problem here was that disasm.o
linked into the bootstrap bpftool was arm64 rather than x86. With the fix
we build two disasm.o, one for the target bpftool in arm64, and one for
the bootstrap bpftool in x86.

Fixes: d510296d ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: NJean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210603170515.1854642-1-jean-philippe@linaro.org
(cherry picked from commit 0779890f)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>

tools/bpf/bpftool/Makefile

@@ -135,7 +135,7 @@ endif
 
 BPFTOOL_BOOTSTRAP := $(BOOTSTRAP_OUTPUT)bpftool
 
-BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o xlated_dumper.o btf_dumper.o) $(OUTPUT)disasm.o
+BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o xlated_dumper.o btf_dumper.o disasm.o)
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
 
 VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\
@@ -179,6 +179,9 @@ endif
 
 CFLAGS += $(if $(BUILD_BPF_SKELS),,-DBPFTOOL_WITHOUT_SKELETONS)
 
+$(BOOTSTRAP_OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
+	$(QUIET_CC)$(HOSTCC) $(CFLAGS) -c -MMD -o $@ $<
+
 $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<