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;