libdw: dwarf_get_units find split units from .dwo.

For a skeleton DIE dwarf_get_units should provide the split DIE as subdie.
This implements that by trying to find the (named) .dwo file and finding
the matching CU in it. The .dwo file is search relative to the current
DWARF or using the comp_dir of the skeleton DIE.

Also fixes a small issue with str_offsets_base_off which is tested in the
new testcase (by getting the name of the split CU DIE).

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

1 files changed, 118 insertions, 0 deletions

diff --git a/libdw/libdw_find_split_unit.c b/libdw/libdw_find_split_unit.c
new file mode 100644
index 00000000..0f74b39a
--- /dev/null
+++ b/libdw/libdw_find_split_unit.c
@@ -0,0 +1,118 @@
+/* Find the split (or skeleton) unit for a given unit.
+   Copyright (C) 2018 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwP.h"
+#include "libelfP.h"
+
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+
+Dwarf_CU *
+internal_function
+__libdw_find_split_unit (Dwarf_CU *cu)
+{
+  /* Only try once.  */
+  if (cu->split != (Dwarf_CU *) -1)
+    return cu->split;
+
+  /* We need a skeleton unit with a comp_dir and [GNU_]dwo_name attributes.
+     The split unit will be the first in the dwo file and should have the
+     same id as the skeleton.  */
+  if (cu->unit_type == DW_UT_skeleton)
+    {
+      Dwarf_Die cudie = CUDIE (cu);
+      Dwarf_Attribute compdir, dwo_name;
+      /* It is fine if compdir doesn't exists, but then dwo_name needs
+	 to be an absolute path.  Also try relative path first.  */
+      dwarf_attr (&cudie, DW_AT_comp_dir, &compdir);
+	if (dwarf_attr (&cudie, DW_AT_dwo_name, &dwo_name) != NULL
+	    || dwarf_attr (&cudie, DW_AT_GNU_dwo_name, &dwo_name) != NULL)
+	{
+	  const char *comp_dir = dwarf_formstring (&compdir);
+	  const char *dwo_file = dwarf_formstring (&dwo_name);
+	  int fd = cu->dbg->elf->fildes;
+	  char *dwo_path = __libdw_filepath (fd, NULL, dwo_file);
+	  if (dwo_path == NULL && comp_dir != NULL)
+	    dwo_path = __libdw_filepath (fd, comp_dir, dwo_file);
+	  if (dwo_path != NULL)
+	    {
+	      int split_fd = open (dwo_path, O_RDONLY);
+	      if (split_fd != -1)
+		{
+		  Dwarf *split_dwarf = dwarf_begin (split_fd, DWARF_C_READ);
+		  if (split_dwarf != NULL)
+		    {
+		      Dwarf_CU *split = NULL;
+		      while (dwarf_get_units (split_dwarf, split, &split,
+					      NULL, NULL, NULL, NULL) == 0)
+			{
+			  if (split->unit_type == DW_UT_split_compile
+			      && cu->unit_id8 == split->unit_id8)
+			    {
+			      /* Link skeleton and split compule units.  */
+			      cu->split = split;
+			      split->split = cu;
+
+			      /* We have everything we need from this
+				 ELF file.  And we are going to close
+				 the fd to not run out of file
+				 descriptors.  */
+			      elf_cntl (split_dwarf->elf, ELF_C_FDDONE);
+			      break;
+			    }
+
+			  if (cu->split == (Dwarf_CU *) -1)
+			    dwarf_end (split_dwarf);
+			}
+		      /* Always close, because we don't want to run
+			 out of file descriptors.  See also the
+			 elf_fcntl ELF_C_FDDONE call above.  */
+		    }
+		  close (split_fd);
+		}
+	      free (dwo_path);
+	    }
+	}
+    }
+
+  /* If we found nothing, make sure we don't try again.  */
+  if (cu->split == (Dwarf_CU *) -1)
+    cu->split = NULL;
+
+  return cu->split;
+}