參考資訊：
https://github.com/nevermosby/linux-bpf-learning/blob/master/bpf/perf-sys.h
問題如下：
$ make M=samples/bpf
make -C /usr/src/linux-source-4.19/samples/bpf/../../tools/lib/bpf/ RM='rm -rf' LDFLAGS= srctree=/usr/src/linux-source-4.19/samples/bpf/../../ O=
Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'
Warning: Kernel ABI header at 'tools/include/uapi/linux/netlink.h' differs from latest version at 'include/uapi/linux/netlink.h'
HOSTCC samples/bpf/bpf_load.o
In file included from ./tools/perf/perf-sys.h:9,
from samples/bpf/bpf_load.c:29:
./tools/perf/perf-sys.h: In function ‘sys_perf_event_open’:
./tools/perf/perf-sys.h:68:15: error: ‘test_attr__enabled’ undeclared (first use in this function)
if (unlikely(test_attr__enabled))
^~~~~~~~~~~~~~~~~~
./tools/include/linux/compiler.h:74:43: note: in definition of macro ‘unlikely’
# define unlikely(x) __builtin_expect(!!(x), 0)
^
./tools/perf/perf-sys.h:68:15: note: each undeclared identifier is reported only once for each function it appears in
if (unlikely(test_attr__enabled))
^~~~~~~~~~~~~~~~~~
./tools/include/linux/compiler.h:74:43: note: in definition of macro ‘unlikely’
# define unlikely(x) __builtin_expect(!!(x), 0)
^
In file included from samples/bpf/bpf_load.c:29:
./tools/perf/perf-sys.h:69:3: warning: implicit declaration of function ‘test_attr__open’ [-Wimplicit-function-declaration]
test_attr__open(attr, pid, cpu, fd, group_fd, flags);
^~~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.host:107: samples/bpf/bpf_load.o] Error 1
make: *** [Makefile:1564: _module_samples/bpf] Error 2
解法如下：
$ vim tools/perf/perf-sys.h
67 #ifdef HAVE_ATTR_TEST
68 //if (unlikely(test_attr__enabled))
69 //test_attr__open(attr, pid, cpu, fd, group_fd, flags);
70 #endif