libbpf-tools/trace_helpers: Fix incorrect DSO information in stacktrace

offcputime may display inaccurate DSO information in the stacktrace.
Here's an example of the issue:

It shows the same DSO offset for different addresses, which is incorrect.
  $ ./offcputime -v
    ..
    iovisor#14 0x00007f8b912a8c (/usr/lib/libcbe.so_0x22afa8c)
    iovisor#15 0x000044000a3ee0 (/usr/lib/libcbe.so_0x22afa8c)
    iovisor#16 0x000044001fc56c (/usr/lib/libcbe.so_0x22afa8c)

This is why syms__map_addr_dso simply returns NULL when syms__find_dso also
returns NULL. In that case, the values of dso_name and dso_offset are not
changed. If the dso_name and dso_offset variables have a garbage value before
calling syms__map_addr_dso, those garbage values are maintained after calling
syms__map_addr_dso.

To ensure consistent usage of DSO info and symbol info, the prototype of
syms__map_addr_dso has been modified to be similar to dladdr[1].

This is the prototype of dladdr:
  int dladdr(void *addr, Dl_info *info);

The information is returned in a Dl_info structure. If no symbol matching addr
could be found, then dli_sname and dli_saddr are set to NULL.
  typedef struct {
      const char *dli_fname;  /* Pathname of shared object that
                                contains address */
      void       *dli_fbase;  /* Base address at which shared
                                object is loaded */
      const char *dli_sname;  /* Name of symbol whose definition
                                overlaps addr */
      void       *dli_saddr;  /* Exact address of symbol named
                                in dli_sname */
   } Dl_info;

Similarly, if no symbol matching the addr could be found, then sym_name and
sym_offset are set to NULL in syms__map_addr_dso of this patch.

Also, apply the modified API usage to offcputime, futexctn, and memleak.

[1] https://man7.org/linux/man-pages/man3/dladdr.3.html

libbpf-tools/futexctn.c

@@ -194,8 +194,7 @@ static int print_stack(struct futexctn_bpf *obj, struct hist_key *info)
 #else
 	const struct syms *syms;
 	const struct sym *sym;
-	char *dso_name;
-	unsigned long dso_offset;
+	struct sym_info sinfo;
 	int idx = 0;
 #endif
 	int i, err = 0, fd;
@@ -245,14 +244,12 @@ static int print_stack(struct futexctn_bpf *obj, struct hist_key *info)
 			else
 				printf("    [unknown]\n");
 		} else {
-			dso_name = NULL;
-			dso_offset = 0;
-			sym = syms__map_addr_dso(syms, ip[i], &dso_name, &dso_offset);
-			printf("    #%-2d 0x%016lx", idx++, ip[i]);
-			if (sym)
-				printf(" %s+0x%lx", sym->name, sym->offset);
-			if (dso_name)
-				printf(" (%s+0x%lx)", dso_name, dso_offset);
+			err = syms__map_addr_dso(syms, ip[i], &sinfo);
+			if (err == 0) {
+				if (sinfo.sym_name)
+					printf(" %s+0x%lx", sinfo.sym_name, sinfo.sym_offset);
+				printf(" (%s+0x%lx)", sinfo.dso_name, sinfo.dso_offset);
+			}
 			printf("\n");
 		}
 	}

libbpf-tools/memleak.c

@@ -766,14 +766,13 @@ void print_stack_frames_by_syms_cache()
 		if (addr == 0)
 			break;
 
-		char *dso_name;
-		uint64_t dso_offset;
-		const struct sym *sym = syms__map_addr_dso(syms, addr, &dso_name, &dso_offset);
-		if (sym) {
-			printf("\t%zu [<%016lx>] %s+0x%lx", i, addr, sym->name, sym->offset);
-			if (dso_name)
-				printf(" [%s]", dso_name);
-			printf("\n");
+		struct sym_info sinfo;
+		int ret = syms__map_addr_dso(syms, addr, &sinfo);
+		if (ret == 0) {
+			printf("\t%zu [<%016lx>]", i, addr);
+			if (sinfo.sym_name)
+				printf(" %s+0x%lx", sinfo.sym_name, sinfo.sym_offset);
+			printf(" [%s]\n", sinfo.dso_name);
 		} else {
 			printf("\t%zu [<%016lx>] <%s>\n", i, addr, "null sym");
 		}

libbpf-tools/offcputime.c

@@ -195,8 +195,7 @@ static void print_map(struct ksyms *ksyms, struct syms_cache *syms_cache,
 	int err, i, ifd, sfd;
 	unsigned long *ip;
 	struct val_t val;
-	char *dso_name;
-	unsigned long dso_offset;
+	struct sym_info sinfo;
 	int idx;
 
 	ip = calloc(env.perf_max_stack_depth, sizeof(*ip));
@@ -262,14 +261,13 @@ static void print_map(struct ksyms *ksyms, struct syms_cache *syms_cache,
 				else
 					printf("    [unknown]\n");
 			} else {
-				dso_name = NULL;
-				dso_offset = 0;
-				sym = syms__map_addr_dso(syms, ip[i], &dso_name, &dso_offset);
 				printf("    #%-2d 0x%016lx", idx++, ip[i]);
-				if (sym)
-					printf(" %s+0x%lx", sym->name, sym->offset);
-				if (dso_name)
-					printf(" (%s+0x%lx)", dso_name, dso_offset);
+				err = syms__map_addr_dso(syms, ip[i], &sinfo);
+				if (err == 0) {
+					if (sinfo.sym_name)
+						printf(" %s+0x%lx", sinfo.sym_name, sinfo.sym_offset);
+					printf(" (%s+0x%lx)", sinfo.dso_name, sinfo.dso_offset);
+				}
 				printf("\n");
 			}
 		}

libbpf-tools/trace_helpers.c

@@ -738,20 +738,29 @@ const struct sym *syms__map_addr(const struct syms *syms, unsigned long addr)
 	return dso__find_sym(dso, offset);
 }
 
-const struct sym *syms__map_addr_dso(const struct syms *syms, unsigned long addr,
-				     char **dso_name, unsigned long *dso_offset)
+int syms__map_addr_dso(const struct syms *syms, unsigned long addr,
+		       struct sym_info *sinfo)
 {
 	struct dso *dso;
+	struct sym *sym;
 	uint64_t offset;
 
+	memset(sinfo, 0x0, sizeof(struct sym_info));
+
 	dso = syms__find_dso(syms, addr, &offset);
 	if (!dso)
-		return NULL;
+		return -1;
 
-	*dso_name = dso->name;
-	*dso_offset = offset;
+	sinfo->dso_name = dso->name;
+	sinfo->dso_offset = offset;
 
-	return dso__find_sym(dso, offset);
+	sym = dso__find_sym(dso, offset);
+	if (sym) {
+		sinfo->sym_name = sym->name;
+		sinfo->sym_offset = sym->offset;
+	}
+
+	return 0;
 }
 
 struct syms_cache {

libbpf-tools/trace_helpers.h

@@ -27,14 +27,21 @@ struct sym {
 	unsigned long offset;
 };
 
+struct sym_info {
+	const char *dso_name;
+	unsigned long dso_offset;
+	const char *sym_name;
+	unsigned long sym_offset;
+};
+
 struct syms;
 
 struct syms *syms__load_pid(int tgid);
 struct syms *syms__load_file(const char *fname);
 void syms__free(struct syms *syms);
 const struct sym *syms__map_addr(const struct syms *syms, unsigned long addr);
-const struct sym *syms__map_addr_dso(const struct syms *syms, unsigned long addr,
-				     char **dso_name, unsigned long *dso_offset);
+int syms__map_addr_dso(const struct syms *syms, unsigned long addr,
+		       struct sym_info *sinfo);
 
 struct syms_cache;