[RFC] Support $ORIGIN in DW_AT_comp_dir

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 1052501c35..afc8d949ec 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -88,6 +88,7 @@ 
 #include <cmath>
 #include <set>
 #include <forward_list>
+#include <regex>
 #include "rust-lang.h"
 #include "gdbsupport/pathstuff.h"
 
@@ -1775,6 +1776,8 @@  static const char *dwarf_bool_name (unsigned int);
 
 static const char *dwarf_type_encoding_name (unsigned int);
 
+static const char *dwarf2_comp_dir (struct die_info *die, struct dwarf2_cu *cu);
+
 static struct die_info *sibling_die (struct die_info *);
 
 static void dump_die_shallow (struct ui_file *, int indent, struct die_info *);
@@ -7211,6 +7214,7 @@  read_cutu_die_from_dwo (struct dwarf2_per_cu_data *this_cu,
   high_pc = NULL;
   ranges = NULL;
   comp_dir = NULL;
+  const char *comp_dir_str = NULL;
 
   if (stub_comp_unit_die != NULL)
     {
@@ -7221,7 +7225,7 @@  read_cutu_die_from_dwo (struct dwarf2_per_cu_data *this_cu,
       low_pc = dwarf2_attr (stub_comp_unit_die, DW_AT_low_pc, cu);
       high_pc = dwarf2_attr (stub_comp_unit_die, DW_AT_high_pc, cu);
       ranges = dwarf2_attr (stub_comp_unit_die, DW_AT_ranges, cu);
-      comp_dir = dwarf2_attr (stub_comp_unit_die, DW_AT_comp_dir, cu);
+      comp_dir_str = dwarf2_comp_dir (stub_comp_unit_die, cu);
 
       /* There should be a DW_AT_addr_base attribute here (if needed).
 	 We need the value before we can process DW_FORM_GNU_addr_index
@@ -7239,13 +7243,15 @@  read_cutu_die_from_dwo (struct dwarf2_per_cu_data *this_cu,
 	cu->ranges_base = DW_UNSND (attr);
     }
   else if (stub_comp_dir != NULL)
+    comp_dir_str = stub_comp_dir;
+  if (comp_dir_str != nullptr)
     {
       /* Reconstruct the comp_dir attribute to simplify the code below.  */
       comp_dir = XOBNEW (&cu->comp_unit_obstack, struct attribute);
       comp_dir->name = DW_AT_comp_dir;
       comp_dir->form = DW_FORM_string;
       DW_STRING_IS_CANONICAL (comp_dir) = 0;
-      DW_STRING (comp_dir) = stub_comp_dir;
+      DW_STRING (comp_dir) = comp_dir_str;
     }
 
   /* Set up for reading the DWO CU/TU.  */
@@ -7388,7 +7394,7 @@  lookup_dwo_unit (struct dwarf2_per_cu_data *this_cu,
 
   /* Yeah, we look dwo_name up again, but it simplifies the code.  */
   dwo_name = dwarf2_dwo_name (comp_unit_die, cu);
-  comp_dir = dwarf2_string_attr (comp_unit_die, DW_AT_comp_dir, cu);
+  comp_dir = dwarf2_comp_dir (comp_unit_die, cu);
 
   if (this_cu->is_debug_types)
     {
@@ -8024,7 +8030,7 @@  process_psymtab_comp_unit_reader (const struct die_reader_specs *reader,
   pst = create_partial_symtab (per_cu, filename);
 
   /* This must be done before calling dwarf2_build_include_psymtabs.  */
-  pst->dirname = dwarf2_string_attr (comp_unit_die, DW_AT_comp_dir, cu);
+  pst->dirname = dwarf2_comp_dir (comp_unit_die, cu);
 
   baseaddr = ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
 
@@ -11414,7 +11420,7 @@  find_file_and_directory (struct die_info *die, struct dwarf2_cu *cu)
   /* Find the filename.  Do not use dwarf2_name here, since the filename
      is not a source language identifier.  */
   res.name = dwarf2_string_attr (die, DW_AT_name, cu);
-  res.comp_dir = dwarf2_string_attr (die, DW_AT_comp_dir, cu);
+  res.comp_dir = dwarf2_comp_dir (die, cu);
 
   if (res.comp_dir == NULL
       && producer_is_gcc_lt_4_3 (cu) && res.name != NULL
@@ -20181,6 +20187,31 @@  dwarf2_string_attr (struct die_info *die, unsigned int name, struct dwarf2_cu *c
   return str;
 }
 
+/* Returns the DW_AT_comp_dir attribute, with $ORIGIN replaced as necessary.
+   Returns the empty string if there is no DW_AT_comp_dir attribute.  */
+static const char *
+dwarf2_comp_dir (struct die_info *die, struct dwarf2_cu *cu)
+{
+  static const char origin_str[] = "$ORIGIN";
+  static constexpr size_t origin_str_len = sizeof(origin_str) - 1;
+
+  const char* comp_dir = dwarf2_string_attr (die, DW_AT_comp_dir, cu);
+  if (comp_dir == nullptr)
+    return nullptr;
+
+  std::string comp_dir_str = comp_dir;
+  if (comp_dir_str.substr (0, origin_str_len) != origin_str)
+    return comp_dir;
+
+  struct objfile *objfile = cu->per_cu->dwarf2_per_objfile->objfile;
+  std::string replaced
+    = ldirname (objfile_name (objfile)) + comp_dir_str.substr (origin_str_len);
+  char *alloc = (char *) obstack_alloc (&objfile->objfile_obstack,
+					replaced.length () + 1);
+  memcpy (alloc, replaced.c_str (), replaced.length () + 1);
+  return alloc;
+}
+
 /* Return the dwo name or NULL if not present. If present, it is in either
    DW_AT_GNU_dwo_name or DW_AT_dwo_name atrribute.  */
 static const char *
diff --git a/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.c b/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.c
new file mode 100644
index 0000000000..f5f2501e95
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.c
@@ -0,0 +1,11 @@ 
+static int func2(void) {
+  return 42;
+}
+
+int
+main (void)
+{
+  int val = func2();
+  return val;
+}
+
diff --git a/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.exp b/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.exp
new file mode 100644
index 0000000000..301cf51fea
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-origin-comp-dir.exp
@@ -0,0 +1,39 @@ 
+# Copyright 2013-2019 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2.
+if ![dwarf2_support] {
+    return 0  
+}
+
+standard_testfile
+
+set pwd [exec pwd -P]
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+	  [list additional_flags=-gsplit-dwarf additional_flags=-fdebug-prefix-map=$pwd=\\\$ORIGIN]] } {
+    return -1
+}
+
+clean_restart $binfile
+gdb_reinitialize_dir "/NoNeXiStInG"
+
+runto_main
+
+gdb_test_no_output "next"
+gdb_test "p val" "42"
+gdb_test "break func2" "Breakpoint .*"