diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6d5f19d04bb..a173113929a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2019-09-12  Mike Gulick  <mgulick@mathworks.com>
+
+	* source.c (prepare_path_for_appending): New function.
+	(openp): Make use of new function.
+	(find_and_open_source): Search for the compilation directory and
+	source file as a relative path beneath the directory search path.
+
 2019-09-12  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* procfs.c (procfs_target::wait) <PR_FAULTED>: Get signal from
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 96c04091973..97c99663985 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,9 @@
+2019-09-12  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.texinfo (Source Path): Additional text to better describe
+	how the source path directory list is used when searching for
+	source files.
+
 2019-09-10  Tom Tromey  <tromey@adacore.com>
 
 	* gdb.texinfo (Index Files): Update Ada text.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 79824a0226a..20ab1e576ec 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -8954,11 +8954,20 @@
 in the list, until it finds a file with the desired name.
 
 For example, suppose an executable references the file
-@file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
-@file{/mnt/cross}.  The file is first looked up literally; if this
-fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
-fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
-message is printed.  @value{GDBN} does not look up the parts of the
+@file{/usr/src/foo-1.0/lib/foo.c} and does not record a compilation
+directory, the @dfn{source path} is @file{/mnt/cross}. @value{GDBN}
+would look for the source file in the following locations:
+
+@enumerate
+
+@item @file{/usr/src/foo-1.0/lib/foo.c}
+@item @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c}
+@item @file{/mnt/cross/foo.c}
+
+@end enumerate
+
+If the source file is not present at any of the above locations then
+an error is printed.  @value{GDBN} does not look up the parts of the
 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
 Likewise, the subdirectories of the source path are not searched: if
 the source path is @file{/mnt/cross}, and the binary refers to
@@ -8966,11 +8975,91 @@
 @file{/mnt/cross/usr/src/foo-1.0/lib}.
 
 Plain file names, relative file names with leading directories, file
-names containing dots, etc.@: are all treated as described above; for
-instance, if the source path is @file{/mnt/cross}, and the source file
-is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
-@file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
-that---@file{/mnt/cross/foo.c}.
+names containing dots, etc.@: are all treated as described above,
+except that non-absolute file names are not looked up literally.  If
+the @dfn{source path} is @file{/mnt/cross}, and the source file is
+recorded as @file{../lib/foo.c} and no compilation directory is
+recorded then @value{GDBN} will search in the following locations:
+
+@enumerate
+
+@item @file{/mnt/cross/../lib/foo.c}
+@item @file{/mnt/cross/foo.c}
+
+@end enumerate
+
+@kindex cdir
+@kindex cwd
+@vindex $cdir@r{, convenience variable}
+@vindex $cwd@r{, convenience variable}
+@cindex compilation directory
+@cindex current directory
+@cindex working directory
+@cindex directory, current
+@cindex directory, compilation
+The @dfn{source path} will always include two special entries
+@samp{$cdir} and @samp{$cwd}, these refer to the compilation directory
+(if one is recorded) and the current workig directory respectively.
+
+@samp{cdir} causes @value{GDBN} to search within the compilation
+directory, if one is recorded in the debug information.  If no
+compilation directory is recorded in the debug information then
+@samp{cdir} is ignored.
+
+@samp{$cwd} is not the same as @samp{.}---the former tracks the
+current working directory as it changes during your @value{GDBN}
+session, while the latter is immediately expanded to the current
+directory at the time you add an entry to the source path.
+
+If a compilation directory is recorded in the debug information, and
+@value{GDBN} has not found the source file after the first search
+using @dfn{source path}, then @value{GDBN} will combine the
+compilation directory and the filename, and then search for the source
+file again using the @dfn{source path}.
+
+For example, if the executable records the source file as
+@file{/usr/src/foo-1.0/lib/foo.c} the compilation directory is
+recorded as @file{/project/build}, and the @dfn{source path} is
+@file{/mnt/cross;$cdir;$cwd} while the current working directory of
+the @value{GDBN} session is @file{/home/user}, then @value{GDBN} will
+search for the source file in the following loctions:
+
+@enumerate
+
+@item @file{/usr/src/foo-1.0/lib/foo.c}
+@item @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c}
+@item @file{/project/build/usr/src/foo-1.0/lib/foo.c}
+@item @file{/home/user/usr/src/foo-1.0/lib/foo.c}
+@item @file{/mnt/cross/project/build/usr/src/foo-1.0/lib/foo.c}
+@item @file{/project/build/project/build/usr/src/foo-1.0/lib/foo.c}
+@item @file{/home/user/project/build/usr/src/foo-1.0/lib/foo.c}
+@item @file{/mnt/cross/foo.c}
+@item @file{/project/build/foo.c}
+@item @file{/home/user/foo.c}
+
+@end enumerate
+
+If the file name in the previous example had been recorded in the
+executable as a relative path rather than an absolute path, then the
+first look up would not have occurred, but all of the remaining steps
+would be similar.
+
+When searching for source files on MS-DOS and MS-Windows, where
+absolute paths start with a drive letter (e.g.
+@file{C:/project/foo.c}), @value{GDBN} will remove the drive letter
+from the file name before appending it to a search directory from
+@dfn{source path}; for instance if the executable references the
+source file @file{C:/project/foo.c} and @dfn{source path} is set to
+@file{D:/mnt/cross}, then @value{GDBN} will search in the following
+locations for the source file:
+
+@enumerate
+
+@item @file{C:/project/foo.c}
+@item @file{D:/mnt/cross/project/foo.c}
+@item @file{D:/mnt/cross/foo.c}
+
+@end enumerate
 
 Note that the executable search path is @emph{not} used to locate the
 source files.
@@ -9058,21 +9147,12 @@
 whitespace.  You may specify a directory that is already in the source
 path; this moves it forward, so @value{GDBN} searches it sooner.
 
-@kindex cdir
-@kindex cwd
-@vindex $cdir@r{, convenience variable}
-@vindex $cwd@r{, convenience variable}
-@cindex compilation directory
-@cindex current directory
-@cindex working directory
-@cindex directory, current
-@cindex directory, compilation
-You can use the string @samp{$cdir} to refer to the compilation
-directory (if one is recorded), and @samp{$cwd} to refer to the current
-working directory.  @samp{$cwd} is not the same as @samp{.}---the former
-tracks the current working directory as it changes during your @value{GDBN}
-session, while the latter is immediately expanded to the current
-directory at the time you add an entry to the source path.
+The special strings @samp{$cdir} (to refer to the compilation
+directory, if one is recorded), and @samp{$cwd} (to refer to the
+current working directory) can also be included in the list of
+directories @var{dirname}.  Though these will already be in the source
+path they will be moved forward in the list so @value{GDBN} searches
+them sooner.
 
 @item directory
 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems).  This requires confirmation.
diff --git a/gdb/source.c b/gdb/source.c
index b27f210802c..ece1ad3d16b 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -654,6 +654,29 @@ info_source_command (const char *ignore, int from_tty)
 }
 
 
+/* Helper function to remove characters from the start of PATH so that
+   PATH can then be appended to a directory name.  We remove leading drive
+   letters (for dos) as well as leading '/' characters and './'
+   sequences.  */
+
+const char *
+prepare_path_for_appending (const char *path)
+{
+  /* For dos paths, d:/foo -> /foo, and d:foo -> foo.  */
+  if (HAS_DRIVE_SPEC (path))
+    path = STRIP_DRIVE_SPEC (path);
+
+  /* /foo => foo, to avoid multiple slashes that Emacs doesn't like.  */
+  while (IS_DIR_SEPARATOR(path[0]))
+    path++;
+
+  /* ./foo => foo */
+  while (path[0] == '.' && IS_DIR_SEPARATOR (path[1]))
+    path += 2;
+
+  return path;
+}
+
 /* Open a file named STRING, searching path PATH (dir names sep by some char)
    using mode MODE in the calls to open.  You cannot use this function to
    create files (O_CREAT).
@@ -747,17 +770,9 @@ openp (const char *path, openp_flags opts, const char *string,
 	    goto done;
     }
 
-  /* For dos paths, d:/foo -> /foo, and d:foo -> foo.  */
-  if (HAS_DRIVE_SPEC (string))
-    string = STRIP_DRIVE_SPEC (string);
-
-  /* /foo => foo, to avoid multiple slashes that Emacs doesn't like.  */
-  while (IS_DIR_SEPARATOR(string[0]))
-    string++;
-
-  /* ./foo => foo */
-  while (string[0] == '.' && IS_DIR_SEPARATOR (string[1]))
-    string += 2;
+  /* Remove characters from the start of PATH that we don't need when PATH
+     is appended to a directory name.  */
+  string = prepare_path_for_appending (string);
 
   alloclen = strlen (path) + strlen (string) + 2;
   filename = (char *) alloca (alloclen);
@@ -1033,7 +1048,32 @@ find_and_open_source (const char *filename,
   openp_flags flags = OPF_SEARCH_IN_PATH;
   if (basenames_may_differ)
     flags |= OPF_RETURN_REALPATH;
+
+  /* Try to locate file using filename.  */
   result = openp (path, flags, filename, OPEN_MODE, fullname);
+  if (result < 0 && dirname != NULL)
+    {
+      /* Remove characters from the start of PATH that we don't need when
+	 PATH is appended to a directory name.  */
+      const char *filename_start = prepare_path_for_appending (filename);
+
+      /* Try to locate file using compilation dir + filename.  This is
+	 helpful if part of the compilation directory was removed,
+	 e.g. using gcc's -fdebug-prefix-map, and we have added the missing
+	 prefix to source_path.  */
+      std::string cdir_filename (dirname);
+
+      /* Remove any trailing directory separators.  */
+      while (IS_DIR_SEPARATOR (cdir_filename.back ()))
+	cdir_filename.pop_back ();
+
+      /* Add our own directory separator.  */
+      cdir_filename.append (SLASH_STRING);
+      cdir_filename.append (filename_start);
+
+      result = openp (path, flags, cdir_filename.c_str (), OPEN_MODE,
+		      fullname);
+    }
   if (result < 0)
     {
       /* Didn't work.  Try using just the basename.  */
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index a51d22ce22f..0d37519a5a4 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-09-12  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.base/source-dir.exp: Add extra test for mapped compilation
+	directory.
+
 2019-09-10  Tom Tromey  <tromey@adacore.com>
 
 	* boards/cc-with-tweaks.exp: Set GNATMAKE_FOR_TARGET.
diff --git a/gdb/testsuite/gdb.base/source-dir.c b/gdb/testsuite/gdb.base/source-dir.c
new file mode 100644
index 00000000000..d94b8074ec0
--- /dev/null
+++ b/gdb/testsuite/gdb.base/source-dir.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 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/>.  */
+
+int
+main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/source-dir.exp b/gdb/testsuite/gdb.base/source-dir.exp
index 048c0e95161..3f9ee69ae45 100644
--- a/gdb/testsuite/gdb.base/source-dir.exp
+++ b/gdb/testsuite/gdb.base/source-dir.exp
@@ -15,9 +15,138 @@
 
 standard_testfile
 
-gdb_start
+# Take a list of directories DIRS, and return a regular expression
+# that will match against the output of the 'directory' command
+# assuming that DIRS are all of the directories that should appear in
+# the results.
+proc search_dir_list { dirs } {
+    set output "\r\nSource directories searched: "
+    append output [join $dirs "\[:;\]"]
 
-set foo "/nOtExStInG"
+    return ${output}
+}
 
-gdb_test "directory $foo/a $foo/b $foo/c" "\r\nSource directories searched: $foo/a\[:;\]$foo/b\[:;\]$foo/c\[:;\]\\\$cdir\[:;\]\\\$cwd"
-gdb_test "directory $foo/b $foo/d $foo/c" "\r\nSource directories searched: $foo/b\[:;\]$foo/d\[:;\]$foo/c\[:;\]$foo/a\[:;\]\\\$cdir\[:;\]\\\$cwd"
+# Check that adding directories to the search path changes the order
+# in which directories are searched.
+proc test_changing_search_directory {} {
+    gdb_start
+
+    set foo "/nOtExStInG"
+
+    gdb_test "directory $foo/a $foo/b $foo/c" \
+	[search_dir_list [list \
+			      "$foo/a" \
+			      "$foo/b" \
+			      "$foo/c" \
+			      "\\\$cdir" \
+			      "\\\$cwd"]]
+    gdb_test "directory $foo/b $foo/d $foo/c" \
+	[search_dir_list [list \
+			      "$foo/b" \
+			      "$foo/d" \
+			      "$foo/c" \
+			      "$foo/a" \
+			      "\\\$cdir" \
+			      "\\\$cwd"]]
+    gdb_exit
+}
+
+# Test that the compilation directory can also be extended with a
+# prefix from the directory search path in order to find source files.
+proc test_truncated_comp_dir {} {
+    global srcfile srcdir subdir binfile
+
+    # When we run this test the current directory will be something
+    # like this:
+    #     /some/path/to/gdb/build/testsuite/
+    # We are going to copy the source file out of the source tree into
+    # a location like this:
+    #     /some/path/to/gdb/build/testsuite/output/gdb.base/soure-dir/
+    #
+    # We will then switch to this directory and compile the source
+    # file, however, we will ask GCC to remove this prefix from the
+    # compilation directory in the debug info:
+    #     /some/path/to/gdb/build/testsuite/output/
+    #
+    # As a result the debug information will look like this:
+    #
+    #     DW_AT_name        : source-dir.c
+    #     DW_AT_comp_dir    : /gdb.base/source-dir
+    #
+    # Finally we switch back to this directory:
+    #     /some/path/to/gdb/build/testsuite/
+    #
+    # and start GDB.  There was a time when GDB would be unable to
+    # find the source file no matter what we added to the directory
+    # search path, this should now be fixed.
+
+    set original_dir [pwd]
+    set working_dir [standard_output_file ""]
+    cd ${working_dir}
+
+    set strip_dir [file normalize "${working_dir}/../.."]
+
+    set new_srcfile [standard_output_file ${srcfile}]
+    set fd [open "$new_srcfile" w]
+    puts $fd "int
+    main ()
+    {
+      return 0;
+    }"
+    close $fd
+
+    set options \
+	"debug additional_flags=-fdebug-prefix-map=${strip_dir}="
+    if  { [gdb_compile "${srcfile}" "${binfile}" \
+	       executable ${options}] != "" } {
+	untested "failed to compile"
+	return -1
+    }
+
+    cd ${original_dir}
+
+    clean_restart ${binfile}
+
+    gdb_test_no_output "set directories \$cdir:\$cwd"
+    gdb_test "show directories" \
+	"\r\nSource directories searched: \\\$cdir\[:;\]\\\$cwd"
+
+    if ![runto_main] then {
+	fail "can't run to main"
+	return 0
+    }
+
+    gdb_test "info source" \
+    [multi_line \
+	 "Current source file is ${srcfile}" \
+	 "Compilation directory is \[^\n\r\]+" \
+	 "${srcfile}: No such file or directory."] \
+	"info source before setting directory search list"
+
+    gdb_test "dir $strip_dir" \
+	[search_dir_list [list \
+			      "$strip_dir" \
+			      "\\\$cdir" \
+			      "\\\$cwd"]]
+    gdb_test "list" [multi_line \
+			 "1\[ \t\]+int" \
+			 "2\[ \t\]+main \\(\\)" \
+			 "3\[ \t\]+\\{" \
+			 "4\[ \t\]+return 0;" \
+			 "5\[ \t\]+\\}" ]
+
+    gdb_test "info source" \
+	[multi_line \
+	     "Current source file is ${srcfile}" \
+	     "Compilation directory is \[^\n\r\]+" \
+	     "Located in ${new_srcfile}" \
+	     "Contains 5 lines." \
+	     "Source language is c." \
+	     "Producer is \[^\n\r\]+" \
+	     "\[^\n\r\]+" \
+	     "\[^\n\r\]+" ] \
+	"info source after setting directory search list"
+}
+
+test_changing_search_directory
+test_truncated_comp_dir
