Re: [PATCH bpf-next] samples: bpf: Fix cross-compiling error about bpftool

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On 2022/7/8 10:46, Pu Lehui wrote:


On 2022/7/8 3:12, Song Liu wrote:


On Jul 7, 2022, at 7:08 AM, Pu Lehui <pulehui@xxxxxxxxxx> wrote:

Currently, when cross compiling bpf samples, the host side
cannot use arch-specific bpftool to generate vmlinux.h or
skeleton. We need to compile the bpftool with the host
compiler.

Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
---
samples/bpf/Makefile | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 5002a5b9a7da..fe54a8c8f312 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
+-include tools/scripts/Makefile.include

Why do we need the -include here?


HOSTLD is defined in tools/scripts/Makefile.include, we need to add it.

And for -include, mainly to resolve some conflicts:
1. If workdir is kernel_src, then 'include tools/scripts/Makefile.include' is fine when 'make M=samples/bpf'.
2. Since the trick in samples/bpf/Makefile:

# Trick to allow make to be run from this directory
all:
     $(MAKE) -C ../../ M=$(CURDIR) BPF_SAMPLES_PATH=$(CURDIR)

If workdir is samples/bpf, the compile process will first load the Makefile in samples/bpf, then change workdir to kernel_src and load the kernel_src's Makefile. So if we just add 'include tools/scripts/Makefile.include', then the first load will occur error for not found the file, so we add -include to skip the first load.

sorry, correct the reply, so we add -include to skip the 'tools/scripts/Makefile.include' file on the fisrt load.


Thanks,
Song


BPF_SAMPLES_PATH ?= $(abspath $(srctree)/$(src))
TOOLS_PATH := $(BPF_SAMPLES_PATH)/../../tools
@@ -283,11 +284,10 @@ $(LIBBPF): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
BPFTOOLDIR := $(TOOLS_PATH)/bpf/bpftool
BPFTOOL_OUTPUT := $(abspath $(BPF_SAMPLES_PATH))/bpftool
BPFTOOL := $(BPFTOOL_OUTPUT)/bpftool
-$(BPFTOOL): $(LIBBPF) $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT) +$(BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT)
        $(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../ \
-        OUTPUT=$(BPFTOOL_OUTPUT)/ \
-        LIBBPF_OUTPUT=$(LIBBPF_OUTPUT)/ \
-        LIBBPF_DESTDIR=$(LIBBPF_DESTDIR)/
+        ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) \
+        OUTPUT=$(BPFTOOL_OUTPUT)/

$(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT):
    $(call msg,MKDIR,$@)
--
2.25.1


.

.



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