tools build: Add capability-related feature detection

Add utilities to help checking capabilities of the running procss. Make
perf link with libcap, if it is available. If no libcap-dev[el], assume
no capabilities.

Committer testing:

$ make O=/tmp/build/perf -C tools/perf install-bin
make: Entering directory '/home/acme/git/perf/tools/perf'
BUILD: Doing 'make -j8' parallel build

Auto-detecting system features:
<SNIP>
... libbfd: [ on ]
... libcap: [ OFF ]
... libelf: [ on ]
<SNIP>
Makefile.config:833: No libcap found, disables capability support, please install libcap-devel/libcap-dev
<SNIP>
$ grep libcap /tmp/build/perf/FEATURE-DUMP
feature-libcap=0
$ cat /tmp/build/perf/feature/test-libcap.make.output
test-libcap.c:2:10: fatal error: sys/capability.h: No such file or directory
2 | #include <sys/capability.h>
| ^~~~~~~~~~~~~~~~~~
compilation terminated.
$

Now install libcap-devel and try again:

$ make O=/tmp/build/perf -C tools/perf install-bin
make: Entering directory '/home/acme/git/perf/tools/perf'
BUILD: Doing 'make -j8' parallel build
Warning: Kernel ABI header at 'tools/include/linux/bits.h' differs from latest version at 'include/linux/bits.h'
diff -u tools/include/linux/bits.h include/linux/bits.h
Warning: Kernel ABI header at 'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version at 'arch/x86/include/asm/cpufeatures.h'
diff -u tools/arch/x86/include/asm/cpufeatures.h arch/x86/include/asm/cpufeatures.h

Auto-detecting system features:
<SNIP>
... libbfd: [ on ]
... libcap: [ on ]
... libelf: [ on ]
<SNIP>>
CC /tmp/build/perf/jvmti/libjvmti.o
<SNIP>>
$ grep libcap /tmp/build/perf/FEATURE-DUMP
feature-libcap=1
$ cat /tmp/build/perf/feature/test-libcap.make.output
$ ldd /tmp/build/perf/feature/test-libcap.make.bin
ldd: /tmp/build/perf/feature/test-libcap.make.bin: No such file or directory
$ ldd /tmp/build/perf/feature/test-libcap.bin
linux-vdso.so.1 (0x00007ffc35bfe000)
libcap.so.2 => /lib64/libcap.so.2 (0x00007ff9c62ff000)
libc.so.6 => /lib64/libc.so.6 (0x00007ff9c6139000)
/lib64/ld-linux-x86-64.so.2 (0x00007ff9c6326000)
$

Signed-off-by: Igor Lubashev <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexey Budankov <[e-mail]>
Cc: James Morris <[e-mail]>
Cc: Mathieu Poirier <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Suzuki Poulouse <[e-mail]>
[ split from a larger patch ]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/Makefile.feature

···
         gtk2-infobar                    \
         libaudit                        \
         libbfd                          \
+        libcap                          \
         libelf                          \
         libelf-getphdrnum               \
         libelf-gelf_getnote             \
···
          gtk2                   \
          libaudit               \
          libbfd                 \
+         libcap                 \
          libelf                 \
          libnuma                \
          numa_num_possible_cpus \

tools/build/feature/Makefile

···
          test-libbfd-liberty.bin                \
          test-libbfd-liberty-z.bin              \
          test-cplus-demangle.bin                \
+         test-libcap.bin			\
          test-libelf.bin                        \
          test-libelf-getphdrnum.bin             \
          test-libelf-gelf_getnote.bin           \
···
 
 $(OUTPUT)test-bionic.bin:
 	$(BUILD)
+
+$(OUTPUT)test-libcap.bin:
+	$(BUILD) -lcap
 
 $(OUTPUT)test-libelf.bin:
 	$(BUILD) -lelf

tools/build/feature/test-libcap.c

···
+// SPDX-License-Identifier: GPL-2.0
+#include <sys/capability.h>
+#include <linux/capability.h>
+
+int main(void)
+{
+	cap_flag_value_t val;
+	cap_t caps = cap_get_proc();
+
+	if (!caps)
+		return 1;
+
+	if (cap_get_flag(caps, CAP_SYS_ADMIN, CAP_EFFECTIVE, &val) != 0)
+		return 1;
+
+	if (cap_free(caps) != 0)
+		return 1;
+
+	return 0;
+}

tools/perf/Makefile.config

···
   endif
 endif
 
+ifndef NO_LIBCAP
+  ifeq ($(feature-libcap), 1)
+    CFLAGS += -DHAVE_LIBCAP_SUPPORT
+    EXTLIBS += -lcap
+    $(call detected,CONFIG_LIBCAP)
+  else
+    msg := $(warning No libcap found, disables capability support, please install libcap-devel/libcap-dev);
+    NO_LIBCAP := 1
+  endif
+endif
+
 ifndef NO_BACKTRACE
   ifeq ($(feature-backtrace), 1)
     CFLAGS += -DHAVE_BACKTRACE_SUPPORT

tools/perf/Makefile.perf

···
 #
 # Define NO_LIBBPF if you do not want BPF support
 #
+# Define NO_LIBCAP if you do not want process capabilities considered by perf
+#
 # Define NO_SDT if you do not want to define SDT event in perf tools,
 # note that it doesn't disable SDT scanning support.
 #