bpftool: Add llvm feature to "bpftool version"

Similarly to "libbfd", add a "llvm" feature to the output of command
"bpftool version" to indicate that LLVM is used for disassembling JIT-ed
programs. This feature is mutually exclusive (from Makefile definitions)
with "libbfd".

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Tested-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221025150329.97371-9-quentin@isovalent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: qmonnet

tools/bpf/bpftool/Documentation/common_options.rst

@@ -7,10 +7,10 @@
 	  Print bpftool's version number (similar to **bpftool version**), the
 	  number of the libbpf version in use, and optional features that were
 	  included when bpftool was compiled. Optional features include linking
-	  against libbfd to provide the disassembler for JIT-ted programs
-	  (**bpftool prog dump jited**) and usage of BPF skeletons (some
-	  features like **bpftool prog profile** or showing pids associated to
-	  BPF objects may rely on it).
+	  against LLVM or libbfd to provide the disassembler for JIT-ted
+	  programs (**bpftool prog dump jited**) and usage of BPF skeletons
+	  (some features like **bpftool prog profile** or showing pids
+	  associated to BPF objects may rely on it).
 
 -j, --json
 	  Generate JSON output. For commands that cannot produce JSON, this

tools/bpf/bpftool/main.c

@@ -119,6 +119,11 @@ static int do_version(int argc, char **argv)
 #else
 	const bool has_libbfd = false;
 #endif
+#ifdef HAVE_LLVM_SUPPORT
+	const bool has_llvm = true;
+#else
+	const bool has_llvm = false;
+#endif
 #ifdef BPFTOOL_WITHOUT_SKELETONS
 	const bool has_skeletons = false;
 #else
@@ -154,6 +159,7 @@ static int do_version(int argc, char **argv)
 		jsonw_name(json_wtr, "features");
 		jsonw_start_object(json_wtr);	/* features */
 		jsonw_bool_field(json_wtr, "libbfd", has_libbfd);
+		jsonw_bool_field(json_wtr, "llvm", has_llvm);
 		jsonw_bool_field(json_wtr, "libbpf_strict", !legacy_libbpf);
 		jsonw_bool_field(json_wtr, "skeletons", has_skeletons);
 		jsonw_bool_field(json_wtr, "bootstrap", bootstrap);
@@ -172,6 +178,7 @@ static int do_version(int argc, char **argv)
 		printf("using libbpf %s\n", libbpf_version_string());
 		printf("features:");
 		print_feature("libbfd", has_libbfd, &nb_features);
+		print_feature("llvm", has_llvm, &nb_features);
 		print_feature("libbpf_strict", !legacy_libbpf, &nb_features);
 		print_feature("skeletons", has_skeletons, &nb_features);
 		print_feature("bootstrap", bootstrap, &nb_features);