perf tools: Set build-id using build-id header on new mmap records

MMAP records that occur after the build-id header is parsed do not have
their build-id set even if the filename matches an entry from the
header. Set the build-id on these dsos as long as the MMAP record
doesn't have its own build-id set.

This fixes an issue with off target analysis where the local version of
a dso is loaded rather than one from ~/.debug via a build-id.

Reported-by: Denis Nikitin <[e-mail]>
Signed-off-by: James Clark <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/dso.h

···
 	enum dso_load_errno	load_errno;
 	u8		 adjust_symbols:1;
 	u8		 has_build_id:1;
+	u8		 header_build_id:1;
 	u8		 has_srcline:1;
 	u8		 hit:1;
 	u8		 annotate_warned:1;

tools/perf/util/header.c

···
 
 		build_id__init(&bid, bev->data, size);
 		dso__set_build_id(dso, &bid);
+		dso->header_build_id = 1;
 
 		if (dso_space != DSO_SPACE__USER) {
 			struct kmod_path m = { .name = NULL, };

tools/perf/util/map.c

···
 
 	if (map != NULL) {
 		char newfilename[PATH_MAX];
-		struct dso *dso;
+		struct dso *dso, *header_bid_dso;
 		int anon, no_dso, vdso, android;
 
 		android = is_android_lib(filename);
···
 		}
 		dso->nsinfo = nsi;
 
-		if (build_id__is_defined(bid))
+		if (build_id__is_defined(bid)) {
 			dso__set_build_id(dso, bid);
-
+		} else {
+			/*
+			 * If the mmap event had no build ID, search for an existing dso from the
+			 * build ID header by name. Otherwise only the dso loaded at the time of
+			 * reading the header will have the build ID set and all future mmaps will
+			 * have it missing.
+			 */
+			down_read(&machine->dsos.lock);
+			header_bid_dso = __dsos__find(&machine->dsos, filename, false);
+			up_read(&machine->dsos.lock);
+			if (header_bid_dso && header_bid_dso->header_build_id) {
+				dso__set_build_id(dso, &header_bid_dso->bid);
+				dso->header_build_id = 1;
+			}
+		}
 		dso__put(dso);
 	}
 	return map;