libdwfl: Handle debugaltlink in dwfl_standard_find_debuginfo.

When we fall back to the debuginfod client then we need to do the
same trick we do for local lookups in dwfl_build_id_find_debuginfo.
If the debug file (dw) is already set, then we must be looking for
the altfile. But we cannot use the actual file/path name given as
hint. We'll have to lookup the alt file "build-id". Because the
debuginfod client only handles build-ids.

Previously we would use the build-id of the main file which meant
the debuginfod client would give us another copy of the debug file,
which would then be set as its own altfile. This caused lots of
confusion...

Signed-off-by: Mark Wielaard <mark@klomp.org>

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index daedaed8fb68408f764af56d30537d062e810270..3f9cd6659b8ff4ca6cb9ba5f3ea5e1aabf5f19a5 100644 (file)
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-30  Mark Wielaard  <mark@klomp.org>
+
+       * find-debuginfo.c (dwfl_standard_find_debuginfo): When mod->dw
+       is already set then try fetching debugaltlink.
+
 2020-04-25  Mark Wielaard  <mark@klomp.org>
 
        * gzip.c (open_stream): Return DWFL_E_NOMEM instead of calling

diff --git a/libdwfl/find-debuginfo.c b/libdwfl/find-debuginfo.c
index 2dd11c48df46d42b02b9870aaa34d6877a91ffa3..4cfd0b8b27b8737270fdca53062e02a2b40ba8d4 100644 (file)
--- a/libdwfl/find-debuginfo.c
+++ b/libdwfl/find-debuginfo.c
@@ -398,8 +398,27 @@ dwfl_standard_find_debuginfo (Dwfl_Module *mod,
       free (canon);
     }
 
-  if (fd < 0 && bits_len > 0)
-    fd = __libdwfl_debuginfod_find_debuginfo (mod->dwfl, bits, bits_len);
+  /* Still nothing? Try if we can use the debuginfod client.
+     But note that we might be looking for the alt file.
+     We use the same trick as dwfl_build_id_find_debuginfo.
+     If the debug file (dw) is already set, then we must be
+     looking for the altfile. But we cannot use the actual
+     file/path name given as hint. We'll have to lookup the
+     alt file "build-id". Because the debuginfod client only
+     handles build-ids.  */
+  if (fd < 0)
+    {
+      if (mod->dw != NULL)
+       {
+         const char *altname;
+         bits_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw, &altname,
+                                                          (const void **)
+                                                          &bits);
+       }
+
+      if (bits_len > 0)
+       fd = __libdwfl_debuginfod_find_debuginfo (mod->dwfl, bits, bits_len);
+    }
 
   return fd;
 }