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tools/bpftool: Fix cross-build

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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 d510296d33 ("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: d510296d33 ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210603170515.1854642-1-jean-philippe@linaro.org
This commit is contained in:
Jean-Philippe Brucker 2021-06-03 19:05:16 +02:00 committed by Daniel Borkmann
parent 56b8b7f953
commit 0779890fed
1 changed files with 4 additions and 1 deletions
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5
tools/bpf/bpftool/Makefile
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@ -136,7 +136,7 @@ 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) \
@ -180,6 +180,9 @@ 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 $@ $<