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bpf: Replace deprecated -target with --target= for Clang
The -target option has been deprecated since clang 3.4 in 2013. Therefore, use
the preferred --target=bpf form instead. This also matches how we use --target=
in scripts/Makefile.clang.
Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://github.com/llvm/llvm-project/commit/274b6f0c87a6a1798de0a68135afc7f95def6277
Link: https://lore.kernel.org/bpf/20230624001856.1903733-1-maskray@google.com
authored by
Fangrui Song
and committed by
Daniel Borkmann
bbaf1ff0
da1a055d
+35
-35
+5
-5
Documentation/bpf/bpf_devel_QA.rst
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Documentation/bpf/bpf_devel_QA.rst
···
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Q: clang flag for target bpf?
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-----------------------------
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Q: In some cases clang flag ``-target bpf`` is used but in other cases the
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Q: In some cases clang flag ``--target=bpf`` is used but in other cases the
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default clang target, which matches the underlying architecture, is used.
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What is the difference and when I should use which?
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A: Although LLVM IR generation and optimization try to stay architecture
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independent, ``-target <arch>`` still has some impact on generated code:
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independent, ``--target=<arch>`` still has some impact on generated code:
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- BPF program may recursively include header file(s) with file scope
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inline assembly codes. The default target can handle this well,
···
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The clang option ``-fno-jump-tables`` can be used to disable
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switch table generation.
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- For clang ``-target bpf``, it is guaranteed that pointer or long /
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- For clang ``--target=bpf``, it is guaranteed that pointer or long /
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unsigned long types will always have a width of 64 bit, no matter
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whether underlying clang binary or default target (or kernel) is
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32 bit. However, when native clang target is used, then it will
···
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while the BPF LLVM back end still operates in 64 bit. The native
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target is mostly needed in tracing for the case of walking ``pt_regs``
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or other kernel structures where CPU's register width matters.
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Otherwise, ``clang -target bpf`` is generally recommended.
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Otherwise, ``clang --target=bpf`` is generally recommended.
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You should use default target when:
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···
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into these structures is verified by the BPF verifier and may result
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in verification failures if the native architecture is not aligned with
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the BPF architecture, e.g. 64-bit. An example of this is
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BPF_PROG_TYPE_SK_MSG require ``-target bpf``
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BPF_PROG_TYPE_SK_MSG require ``--target=bpf``
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.. Links
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Documentation/bpf/btf.rst
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Documentation/bpf/btf.rst
···
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} g2;
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int main() { return 0; }
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int test() { return 0; }
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-bash-4.4$ clang -c -g -O2 -target bpf t2.c
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-bash-4.4$ clang -c -g -O2 --target=bpf t2.c
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-bash-4.4$ readelf -S t2.o
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......
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[ 8] .BTF PROGBITS 0000000000000000 00000247
···
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[10] .rel.BTF.ext REL 0000000000000000 000007e0
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0000000000000040 0000000000000010 16 9 8
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......
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-bash-4.4$ clang -S -g -O2 -target bpf t2.c
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-bash-4.4$ clang -S -g -O2 --target=bpf t2.c
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-bash-4.4$ cat t2.s
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......
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.section .BTF,"",@progbits
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Documentation/bpf/llvm_reloc.rst
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Documentation/bpf/llvm_reloc.rst
···
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return g1 + g2 + l1 + l2;
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}
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-
Compiled with ``clang -target bpf -O2 -c test.c``, the following is
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Compiled with ``clang --target=bpf -O2 -c test.c``, the following is
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the code with ``llvm-objdump -dr test.o``::
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0: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
···
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return gfunc(a, b) + lfunc(a, b) + global;
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}
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-
Compiled with ``clang -target bpf -O2 -c test.c``, we will have
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Compiled with ``clang --target=bpf -O2 -c test.c``, we will have
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following code with `llvm-objdump -dr test.o``::
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Disassembly of section .text:
···
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int global() { return 0; }
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struct t { void *g; } gbl = { global };
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Compiled with ``clang -target bpf -O2 -g -c test.c``, we will see a
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Compiled with ``clang --target=bpf -O2 -g -c test.c``, we will see a
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relocation below in ``.data`` section with command
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``llvm-readelf -r test.o``::
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+1
-1
drivers/hid/bpf/entrypoints/Makefile
+1
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drivers/hid/bpf/entrypoints/Makefile
···
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$(OUTPUT)/entrypoints.bpf.o: entrypoints.bpf.c $(OUTPUT)/vmlinux.h $(BPFOBJ) | $(OUTPUT)
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$(call msg,BPF,$@)
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$(Q)$(CLANG) -g -O2 -target bpf $(INCLUDES) \
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$(Q)$(CLANG) -g -O2 --target=bpf $(INCLUDES) \
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-c $(filter %.c,$^) -o $@ && \
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$(LLVM_STRIP) -g $@
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+1
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kernel/bpf/preload/iterators/Makefile
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kernel/bpf/preload/iterators/Makefile
···
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$(OUTPUT)/%/iterators.bpf.o: iterators.bpf.c $(BPFOBJ) | $(OUTPUT)
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$(call msg,BPF,$@)
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$(Q)mkdir -p $(@D)
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$(Q)$(CLANG) -g -O2 -target bpf -m$* $(INCLUDES) \
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$(Q)$(CLANG) -g -O2 --target=bpf -m$* $(INCLUDES) \
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-c $(filter %.c,$^) -o $@ && \
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$(LLVM_STRIP) -g $@
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+3
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samples/bpf/Makefile
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samples/bpf/Makefile
···
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BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
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BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')
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BTF_LLVM_PROBE := $(shell echo "int main() { return 0; }" | \
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$(CLANG) -target bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
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$(CLANG) --target=bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
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$(LLVM_READELF) -S ./llvm_btf_verify.o | grep BTF; \
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/bin/rm -f ./llvm_btf_verify.o)
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···
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clean-files += vmlinux.h
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# Get Clang's default includes on this system, as opposed to those seen by
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# '-target bpf'. This fixes "missing" files on some architectures/distros,
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# '--target=bpf'. This fixes "missing" files on some architectures/distros,
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# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
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#
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# Use '-idirafter': Don't interfere with include mechanics except where the
···
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$(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h $(src)/xdp_sample_shared.h
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@echo " CLANG-BPF " $@
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$(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(SRCARCH) \
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$(Q)$(CLANG) -g -O2 --target=bpf -D__TARGET_ARCH_$(SRCARCH) \
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-Wno-compare-distinct-pointer-types -I$(srctree)/include \
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-I$(srctree)/samples/bpf -I$(srctree)/tools/include \
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-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
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samples/bpf/gnu/stubs.h
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samples/bpf/gnu/stubs.h
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samples/bpf/test_lwt_bpf.sh
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samples/bpf/test_lwt_bpf.sh
···
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SRC_MAC=$(lookup_mac $VETH0)
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DST_IFINDEX=$(cat /sys/class/net/$VETH0/ifindex)
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CLANG_OPTS="-O2 -target bpf -I ../include/"
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CLANG_OPTS="-O2 --target=bpf -I ../include/"
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CLANG_OPTS+=" -DSRC_MAC=$SRC_MAC -DDST_MAC=$DST_MAC -DDST_IFINDEX=$DST_IFINDEX"
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clang $CLANG_OPTS -c $PROG_SRC -o $BPF_PROG
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+3
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samples/hid/Makefile
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samples/hid/Makefile
···
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BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
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BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')
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BTF_LLVM_PROBE := $(shell echo "int main() { return 0; }" | \
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$(CLANG) -target bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
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$(CLANG) --target=bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
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$(LLVM_READELF) -S ./llvm_btf_verify.o | grep BTF; \
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/bin/rm -f ./llvm_btf_verify.o)
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···
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clean-files += vmlinux.h
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# Get Clang's default includes on this system, as opposed to those seen by
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# '-target bpf'. This fixes "missing" files on some architectures/distros,
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# '--target=bpf'. This fixes "missing" files on some architectures/distros,
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# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
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#
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# Use '-idirafter': Don't interfere with include mechanics except where the
···
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$(obj)/%.bpf.o: $(src)/%.bpf.c $(EXTRA_BPF_HEADERS_SRC) $(obj)/vmlinux.h
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@echo " CLANG-BPF " $@
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$(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(SRCARCH) \
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$(Q)$(CLANG) -g -O2 --target=bpf -D__TARGET_ARCH_$(SRCARCH) \
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-Wno-compare-distinct-pointer-types -I$(srctree)/include \
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-I$(srctree)/samples/bpf -I$(srctree)/tools/include \
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-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
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tools/bpf/bpftool/Documentation/bpftool-gen.rst
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tools/bpf/bpftool/Documentation/bpftool-gen.rst
···
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This is example BPF application with two BPF programs and a mix of BPF maps
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and global variables. Source code is split across two source code files.
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**$ clang -target bpf -g example1.bpf.c -o example1.bpf.o**
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**$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o**
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**$ clang -target bpf -g example2.bpf.c -o example2.bpf.o**
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**$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o**
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**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
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+1
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tools/bpf/bpftool/Makefile
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tools/bpf/bpftool/Makefile
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tools/bpf/runqslower/Makefile
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tools/bpf/runqslower/Makefile
···
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$(QUIET_GEN)$(BPFTOOL) gen skeleton $< > $@
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$(OUTPUT)/%.bpf.o: %.bpf.c $(BPFOBJ) | $(OUTPUT)
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$(QUIET_GEN)$(CLANG) -g -O2 -target bpf $(INCLUDES) \
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$(QUIET_GEN)$(CLANG) -g -O2 --target=bpf $(INCLUDES) \
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-c $(filter %.c,$^) -o $@ && \
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$(LLVM_STRIP) -g $@
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+1
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tools/build/feature/Makefile
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tools/build/feature/Makefile
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tools/testing/selftests/bpf/Makefile
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tools/testing/selftests/bpf/Makefile
···
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OUTPUT=$(HOST_BUILD_DIR)/resolve_btfids/ BPFOBJ=$(HOST_BPFOBJ)
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# Get Clang's default includes on this system, as opposed to those seen by
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# '-target bpf'. This fixes "missing" files on some architectures/distros,
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# '--target=bpf'. This fixes "missing" files on some architectures/distros,
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# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
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#
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# Use '-idirafter': Don't interfere with include mechanics except where the
···
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# $3 - CFLAGS
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define CLANG_BPF_BUILD_RULE
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$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
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$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -mcpu=v3 -o $2
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$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v3 -o $2
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endef
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# Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
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define CLANG_NOALU32_BPF_BUILD_RULE
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$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
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$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -mcpu=v2 -o $2
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$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v2 -o $2
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endef
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# Build BPF object using GCC
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define GCC_BPF_BUILD_RULE
+1
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tools/testing/selftests/bpf/gnu/stubs.h
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tools/testing/selftests/bpf/gnu/stubs.h
+3
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tools/testing/selftests/hid/Makefile
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-3
tools/testing/selftests/hid/Makefile
···
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OUTPUT=$(HOST_BUILD_DIR)/resolve_btfids/ BPFOBJ=$(HOST_BPFOBJ)
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# Get Clang's default includes on this system, as opposed to those seen by
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# '-target bpf'. This fixes "missing" files on some architectures/distros,
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# '--target=bpf'. This fixes "missing" files on some architectures/distros,
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# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
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#
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# Use '-idirafter': Don't interfere with include mechanics except where the
···
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# $3 - CFLAGS
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define CLANG_BPF_BUILD_RULE
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$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
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$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -mcpu=v3 -o $2
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$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v3 -o $2
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endef
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# Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
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define CLANG_NOALU32_BPF_BUILD_RULE
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$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
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$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -mcpu=v2 -o $2
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$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v2 -o $2
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endef
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# Build BPF object using GCC
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define GCC_BPF_BUILD_RULE
+2
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tools/testing/selftests/net/Makefile
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tools/testing/selftests/net/Makefile
···
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mkdir -p $@
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# Get Clang's default includes on this system, as opposed to those seen by
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# '-target bpf'. This fixes "missing" files on some architectures/distros,
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# '--target=bpf'. This fixes "missing" files on some architectures/distros,
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# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
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#
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# Use '-idirafter': Don't interfere with include mechanics except where the
···
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CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
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$(OUTPUT)/nat6to4.o: nat6to4.c $(BPFOBJ) | $(MAKE_DIRS)
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$(CLANG) -O2 -target bpf -c $< $(CCINCLUDE) $(CLANG_SYS_INCLUDES) -o $@
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$(CLANG) -O2 --target=bpf -c $< $(CCINCLUDE) $(CLANG_SYS_INCLUDES) -o $@
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$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \
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$(APIDIR)/linux/bpf.h \
+1
-1
tools/testing/selftests/tc-testing/Makefile
+1
-1
tools/testing/selftests/tc-testing/Makefile