libdwfl: Check for kernel debuginfo file without .debug extension as well

Elfutils, looking for kernel debuginfo file, tries to find it at
various places. If elfutils finds /boot/vmlinu*x* file, it checks
for debufginfo section. If debuginfo is not present, it saves it as
'main elf' and continue looking for debuginfo file having .debug
extension i.e. vmlinux-RELEASE.debug.

'Ubuntu on powerpc' installs kernel as /boot/vmlinux and installs
debuginfo without any extension as /usr/lib/debug/boot/vmlinux-RELEASE
and hence, elfutils is not able to find the debuginfo file.

Here is the launchpad bug for the same:
  https://bugs.launchpad.net/ubuntu/+source/systemtap/+bug/1537125

This patch adds functionality to search for a kernel or debuginfo file
both with and without .debug extension.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Signed-off-by: Mark Wielaard <mjw@redhat.com>

3 files changed, 36 insertions, 9 deletions

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 69fd2337..462a61d0 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,13 @@
+2016-02-22  Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
+	    Mark Wielaard  <mjw@redhat.com>
+
+	* find-debuginfo.c (find_debuginfo_in_path): Remember whether
+	debuglink_file is NULL. Try file basename (without .debug) ofr
+	absolute and relative path if debug_file was NULL.
+	* linux-kernel-modules.c (try_kernel_name): If try_debug is true call
+	dwfl_standard_find_debuginfo with NULL debuglink_file, otherwise with
+	basename of fname.
+
 2016-02-13  Mark Wielaard  <mjw@redhat.com>
 
 	* linux-proc-maps.c (proc_maps_report): Free last_file when ENOEXEC.
diff --git a/libdwfl/find-debuginfo.c b/libdwfl/find-debuginfo.c
index 72461bc3..80515dbd 100644
--- a/libdwfl/find-debuginfo.c
+++ b/libdwfl/find-debuginfo.c
@@ -163,7 +163,11 @@ find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 
   const char *file_basename = file_name == NULL ? NULL : basename (file_name);
   char *localname = NULL;
-  if (debuglink_file == NULL)
+
+  /* We invent a debuglink .debug name if NULL, but then want to try the
+     basename too.  */
+  bool debuglink_null = debuglink_file == NULL;
+  if (debuglink_null)
     {
       /* For a alt debug multi file we need a name, for a separate debug
 	 name we may be able to fall back on file_basename.debug.  */
@@ -231,6 +235,10 @@ find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 	check = *p++ == '+';
       check = check && cancheck;
 
+      /* Try the basename too, if we made up the debuglink name and this
+	 is not the main directory.  */
+      bool try_file_basename;
+
       const char *dir, *subdir, *file;
       switch (p[0])
 	{
@@ -239,6 +247,7 @@ find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 	  dir = file_dirname;
 	  subdir = NULL;
 	  file = debuglink_file;
+	  try_file_basename = false;
 	  break;
 	case '/':
 	  /* An absolute path says to look there for a subdirectory
@@ -268,6 +277,7 @@ find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 	      subdir = NULL;
 	      file = basename (debuglink_file);
 	    }
+	  try_file_basename = debuglink_null;
 	  break;
 	default:
 	  /* A relative path says to try a subdirectory of that name
@@ -275,11 +285,14 @@ find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 	  dir = file_dirname;
 	  subdir = p;
 	  file = debuglink_file;
+	  try_file_basename = debuglink_null;
 	  break;
 	}
 
       char *fname = NULL;
       int fd = try_open (&main_stat, dir, subdir, file, &fname);
+      if (fd < 0 && try_file_basename)
+	fd = try_open (&main_stat, dir, subdir, file_basename, &fname);
       if (fd < 0)
 	switch (errno)
 	  {
diff --git a/libdwfl/linux-kernel-modules.c b/libdwfl/linux-kernel-modules.c
index 79faf994..54c0b908 100644
--- a/libdwfl/linux-kernel-modules.c
+++ b/libdwfl/linux-kernel-modules.c
@@ -92,17 +92,21 @@ try_kernel_name (Dwfl *dwfl, char **fname, bool try_debug)
   if (fd < 0)
     {
       Dwfl_Module fakemod = { .dwfl = dwfl };
-      /* First try the file's unadorned basename as DEBUGLINK_FILE,
-	 to look for "vmlinux" files.  */
-      fd = INTUSE(dwfl_standard_find_debuginfo) (&fakemod, NULL, NULL, 0,
-						 *fname, basename (*fname), 0,
-						 &fakemod.debug.name);
-      if (fd < 0 && try_debug)
-	/* Next, let the call use the default of basename + ".debug",
-	   to look for "vmlinux.debug" files.  */
+
+      if (try_debug)
+	/* Passing NULL for DEBUGLINK_FILE searches for both the basenamer
+	   "vmlinux" and the default of basename + ".debug", to look for
+	   "vmlinux.debug" files.  */
 	fd = INTUSE(dwfl_standard_find_debuginfo) (&fakemod, NULL, NULL, 0,
 						   *fname, NULL, 0,
 						   &fakemod.debug.name);
+      else
+	/* Try the file's unadorned basename as DEBUGLINK_FILE,
+	   to look only for "vmlinux" files.  */
+	fd = INTUSE(dwfl_standard_find_debuginfo) (&fakemod, NULL, NULL, 0,
+						   *fname, basename (*fname),
+						   0, &fakemod.debug.name);
+
       if (fakemod.debug.name != NULL)
 	{
 	  free (*fname);