perf build: Stop using __weak bpf_object__next_map() to handle older libbpf versions

By adding a feature test for bpf_object__next_map() and providing a fallback if
it isn't present in older versions of libbpf.

Committer testing:

$ rpm -q libbpf-devel
libbpf-devel-0.4.0-2.fc35.x86_64
$ make -C tools/perf LIBBPF_DYNAMIC=1 O=/tmp/build/perf install-bin
$ cat /tmp/build/perf/feature/test-libbpf-bpf_object__next_map.make.output
test-libbpf-bpf_object__next_map.c: In function ‘main’:
test-libbpf-bpf_object__next_map.c:6:9: error: implicit declaration of function ‘bpf_object__next_map’; did you mean ‘bpf_object__next’? [-Werror=implicit-function-declaration]
6 | bpf_object__next_map(NULL /* obj */, NULL /* prev */);
| ^~~~~~~~~~~~~~~~~~~~
| bpf_object__next
cc1: all warnings being treated as errors
$
$ objdump -dS /tmp/build/perf/perf | grep '<bpf_object__next_map>:' -A20
00000000005b2e00 <bpf_object__next_map>:
{
5b2e00: 55 push %rbp
5b2e01: 48 89 e5 mov %rsp,%rbp
5b2e04: 48 83 ec 10 sub $0x10,%rsp
5b2e08: 64 48 8b 04 25 28 00 mov %fs:0x28,%rax
5b2e0f: 00 00
5b2e11: 48 89 45 f8 mov %rax,-0x8(%rbp)
5b2e15: 31 c0 xor %eax,%eax
return bpf_map__next(prev, obj);
5b2e17: 48 8b 45 f8 mov -0x8(%rbp),%rax
5b2e1b: 64 48 2b 04 25 28 00 sub %fs:0x28,%rax
5b2e22: 00 00
5b2e24: 75 0f jne 5b2e35 <bpf_object__next_map+0x35>
}
5b2e26: c9 leave
5b2e27: 49 89 f8 mov %rdi,%r8
5b2e2a: 48 89 f7 mov %rsi,%rdi
return bpf_map__next(prev, obj);
5b2e2d: 4c 89 c6 mov %r8,%rsi
5b2e30: e9 cb b1 e5 ff jmp 40e000 <bpf_map__next@plt>
$

Signed-off-by: Jiri Olsa <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ilya Leoshkevich <[e-mail]>
Cc: Sumanth Korikkar <[e-mail]>
Cc: Sven Schnelle <[e-mail]>
Cc: Thomas Richter <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Link: http://lore.kernel.org/linux-perf-users/YozLKby7ITEtchC9@krava
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/Makefile.feature

···
          libbpf-btf__load_from_kernel_by_id \
          libbpf-bpf_prog_load           \
          libbpf-bpf_object__next_program \
+         libbpf-bpf_object__next_map    \
          libpfm4                        \
          libdebuginfod			\
          clang-bpf-co-re

tools/build/feature/Makefile

···
          test-libbpf-btf__load_from_kernel_by_id.bin	\
          test-libbpf-bpf_prog_load.bin          \
          test-libbpf-bpf_object__next_program.bin \
+         test-libbpf-bpf_object__next_map.bin   \
          test-get_cpuid.bin                     \
          test-sdt.bin                           \
          test-cxx.bin                           \
···
 	$(BUILD) -lbpf
 
 $(OUTPUT)test-libbpf-bpf_object__next_program.bin:
+	$(BUILD) -lbpf
+
+$(OUTPUT)test-libbpf-bpf_object__next_map.bin:
 	$(BUILD) -lbpf
 
 $(OUTPUT)test-sdt.bin:

tools/build/feature/test-libbpf-bpf_object__next_map.c

···
+// SPDX-License-Identifier: GPL-2.0
+#include <bpf/libbpf.h>
+
+int main(void)
+{
+	bpf_object__next_map(NULL /* obj */, NULL /* prev */);
+	return 0;
+}

tools/perf/Makefile.config

···
           ifeq ($(feature-libbpf-bpf_object__next_program), 1)
             CFLAGS += -DHAVE_LIBBPF_BPF_OBJECT__NEXT_PROGRAM
           endif
+          $(call feature_check,libbpf-bpf_object__next_map)
+          ifeq ($(feature-libbpf-bpf_object__next_map), 1)
+            CFLAGS += -DHAVE_LIBBPF_BPF_OBJECT__NEXT_MAP
+          endif
         else
           dummy := $(error Error: No libbpf devel library found, please install libbpf-devel);
         endif
···
 	CFLAGS += -DHAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
         CFLAGS += -DHAVE_LIBBPF_BPF_PROG_LOAD
         CFLAGS += -DHAVE_LIBBPF_BPF_OBJECT__NEXT_PROGRAM
+        CFLAGS += -DHAVE_LIBBPF_BPF_OBJECT__NEXT_MAP
       endif
     endif
 

tools/perf/util/bpf-event.c

···
 }
 #endif
 
-struct bpf_map * __weak
+#ifndef HAVE_LIBBPF_BPF_OBJECT__NEXT_MAP
+struct bpf_map *
 bpf_object__next_map(const struct bpf_object *obj, const struct bpf_map *prev)
 {
 #pragma GCC diagnostic push
···
 	return bpf_map__next(prev, obj);
 #pragma GCC diagnostic pop
 }
+#endif
 
 const void * __weak
 btf__raw_data(const struct btf *btf_ro, __u32 *size)