perf build: detect support for libbpf's emit_strings option

This creates a config option that detects libbpf's ability to display
character arrays as strings, which was just added to the BPF tree
(https://git.kernel.org/bpf/bpf-next/c/87c9c79a02b4).

To test this change, I built perf (from later in this patch set) with:

 - static libbpf (default, using source from kernel tree)
 - dynamic libbpf (LIBBPF_DYNAMIC=1 LIBBPF_INCLUDE=/usr/local/include)

For both the static and dynamic versions, I used headers with and without
the ".emit_strings" option.

I verified that of the four resulting binaries, the two with
".emit_strings" would successfully record BPF_METADATA events, and the two
without wouldn't.  All four binaries would successfully display
BPF_METADATA events, because the relevant bit of libbpf code is only used
during "perf record".

Signed-off-by: Blake Jones <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

Author: blakej11

tools/build/Makefile.feature

@@ -126,6 +126,7 @@ FEATURE_TESTS_EXTRA :=                  \
          llvm                           \
          clang                          \
          libbpf                         \
+         libbpf-strings                 \
          libpfm4                        \
          libdebuginfod			\
          clang-bpf-co-re		\

tools/build/feature/Makefile

@@ -59,6 +59,7 @@ FILES=                                          \
          test-lzma.bin                          \
          test-bpf.bin                           \
          test-libbpf.bin                        \
+         test-libbpf-strings.bin                \
          test-get_cpuid.bin                     \
          test-sdt.bin                           \
          test-cxx.bin                           \
@@ -339,6 +340,9 @@ $(OUTPUT)test-bpf.bin:
 $(OUTPUT)test-libbpf.bin:
 	$(BUILD) -lbpf
 
+$(OUTPUT)test-libbpf-strings.bin:
+	$(BUILD)
+
 $(OUTPUT)test-sdt.bin:
 	$(BUILD)
 

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

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <bpf/btf.h>
+
+int main(void)
+{
+	struct btf_dump_type_data_opts opts;
+
+	opts.emit_strings = 0;
+	return opts.emit_strings;
+}

tools/perf/Documentation/perf-check.txt

@@ -52,6 +52,7 @@ feature::
                 dwarf-unwind            /  HAVE_DWARF_UNWIND_SUPPORT
                 auxtrace                /  HAVE_AUXTRACE_SUPPORT
                 libbfd                  /  HAVE_LIBBFD_SUPPORT
+                libbpf-strings          /  HAVE_LIBBPF_STRINGS_SUPPORT
                 libcapstone             /  HAVE_LIBCAPSTONE_SUPPORT
                 libcrypto               /  HAVE_LIBCRYPTO_SUPPORT
                 libdw-dwarf-unwind      /  HAVE_LIBDW_SUPPORT

tools/perf/Makefile.config

@@ -595,8 +595,16 @@ ifndef NO_LIBELF
           LIBBPF_STATIC := 1
           $(call detected,CONFIG_LIBBPF)
           CFLAGS += -DHAVE_LIBBPF_SUPPORT
+	  LIBBPF_INCLUDE = $(LIBBPF_DIR)/..
         endif
       endif
+
+      FEATURE_CHECK_CFLAGS-libbpf-strings="-I$(LIBBPF_INCLUDE)"
+      $(call feature_check,libbpf-strings)
+      ifeq ($(feature-libbpf-strings), 1)
+        $(call detected,CONFIG_LIBBPF_STRINGS)
+        CFLAGS += -DHAVE_LIBBPF_STRINGS_SUPPORT
+      endif
     endif
   endif # NO_LIBBPF
 endif # NO_LIBELF

tools/perf/builtin-check.c

@@ -43,6 +43,7 @@ struct feature_status supported_features[] = {
 	FEATURE_STATUS("dwarf-unwind", HAVE_DWARF_UNWIND_SUPPORT),
 	FEATURE_STATUS("auxtrace", HAVE_AUXTRACE_SUPPORT),
 	FEATURE_STATUS_TIP("libbfd", HAVE_LIBBFD_SUPPORT, "Deprecated, license incompatibility, use BUILD_NONDISTRO=1 and install binutils-dev[el]"),
+	FEATURE_STATUS("libbpf-strings", HAVE_LIBBPF_STRINGS_SUPPORT),
 	FEATURE_STATUS("libcapstone", HAVE_LIBCAPSTONE_SUPPORT),
 	FEATURE_STATUS("libcrypto", HAVE_LIBCRYPTO_SUPPORT),
 	FEATURE_STATUS("libdw-dwarf-unwind", HAVE_LIBDW_SUPPORT),