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clang started to error on invalid asm clobber usage in x86 headers
and many bpf program samples failed to build with the message:
CLANG-bpf /data/users/ast/bpf-next/samples/bpf/xdp_redirect_kern.o
In file included from /data/users/ast/bpf-next/samples/bpf/xdp_redirect_kern.c:14:
In file included from ../include/linux/in.h:23:
In file included from ../include/uapi/linux/in.h:24:
In file included from ../include/linux/socket.h:8:
In file included from ../include/linux/uio.h:14:
In file included from ../include/crypto/hash.h:16:
In file included from ../include/linux/crypto.h:26:
In file included from ../include/linux/uaccess.h:5:
In file included from ../include/linux/sched.h:15:
In file included from ../include/linux/sem.h:5:
In file included from ../include/uapi/linux/sem.h:5:
In file included from ../include/linux/ipc.h:9:
In file included from ../include/linux/refcount.h:72:
../arch/x86/include/asm/refcount.h:72:36: error: asm-specifier for input or output variable conflicts with asm clobber list
r->refs.counter, e, "er", i, "cx");
^
../arch/x86/include/asm/refcount.h:86:27: error: asm-specifier for input or output variable conflicts with asm clobber list
r->refs.counter, e, "cx");
^
2 errors generated.
Override volatile() to workaround the problem.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
eBPF sample programs
====================
This directory contains a test stubs, verifier test-suite and examples
for using eBPF. The examples use libbpf from tools/lib/bpf.
Build dependencies
==================
Compiling requires having installed:
* clang >= version 3.4.0
* llvm >= version 3.7.1
Note that LLVM's tool 'llc' must support target 'bpf', list version
and supported targets with command: ``llc --version``
Kernel headers
--------------
There are usually dependencies to header files of the current kernel.
To avoid installing devel kernel headers system wide, as a normal
user, simply call::
make headers_install
This will creates a local "usr/include" directory in the git/build top
level directory, that the make system automatically pickup first.
Compiling
=========
For building the BPF samples, issue the below command from the kernel
top level directory::
make samples/bpf/
Do notice the "/" slash after the directory name.
It is also possible to call make from this directory. This will just
hide the the invocation of make as above with the appended "/".
Manually compiling LLVM with 'bpf' support
------------------------------------------
Since version 3.7.0, LLVM adds a proper LLVM backend target for the
BPF bytecode architecture.
By default llvm will build all non-experimental backends including bpf.
To generate a smaller llc binary one can use::
-DLLVM_TARGETS_TO_BUILD="BPF"
Quick sniplet for manually compiling LLVM and clang
(build dependencies are cmake and gcc-c++)::
$ git clone http://llvm.org/git/llvm.git
$ cd llvm/tools
$ git clone --depth 1 http://llvm.org/git/clang.git
$ cd ..; mkdir build; cd build
$ cmake .. -DLLVM_TARGETS_TO_BUILD="BPF;X86"
$ make -j $(getconf _NPROCESSORS_ONLN)
It is also possible to point make to the newly compiled 'llc' or
'clang' command via redefining LLC or CLANG on the make command line::
make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
Cross compiling samples
-----------------------
In order to cross-compile, say for arm64 targets, export CROSS_COMPILE and ARCH
environment variables before calling make. This will direct make to build
samples for the cross target.
export ARCH=arm64
export CROSS_COMPILE="aarch64-linux-gnu-"
make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
636e78b1cd