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 <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/linux-perf-users/YozLKby7ITEtchC9@kravaSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.feature

@@ -101,6 +101,7 @@ FEATURE_TESTS_EXTRA :=                  \
          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

@@ -60,6 +60,7 @@ FILES=                                          \
          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                           \
@@ -299,6 +300,9 @@ $(OUTPUT)test-libbpf-bpf_prog_load.bin:
 $(OUTPUT)test-libbpf-bpf_object__next_program.bin:
 	$(BUILD) -lbpf
 
+$(OUTPUT)test-libbpf-bpf_object__next_map.bin:
+	$(BUILD) -lbpf
+
 $(OUTPUT)test-sdt.bin:
 	$(BUILD)
 

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

@@ -581,6 +581,10 @@ ifndef NO_LIBELF
           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
@@ -588,6 +592,7 @@ ifndef NO_LIBELF
 	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

@@ -61,7 +61,8 @@ bpf_object__next_program(const struct bpf_object *obj, struct bpf_program *prev)
 }
 #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
@@ -69,6 +70,7 @@ bpf_object__next_map(const struct bpf_object *obj, const struct bpf_map *prev)
 	return bpf_map__next(prev, obj);
 #pragma GCC diagnostic pop
 }
+#endif
 
 const void * __weak
 btf__raw_data(const struct btf *btf_ro, __u32 *size)