gdb: Look for compilation directory relative to directory search path

The 'directory' command allows the user to provide a list of filesystem
directories in which to search for source code.  The directories in this
search path are used as the base directory for the source filename from
the debug information (DW_AT_name).  Thus the directory search path
provides alternatives to the existing compilation directory from the
debug information (DW_AT_comp_dir).  Generally speaking, DW_AT_name
stores the filename argument passed to the compiler (including any
directory components), and DW_AT_comp_dir stores the current working
directory from which the compiler was executed.  For example:

    $ cd /path/to/project/subdir1
    $ gcc -c a/test.c -g

The corresponding debug information will look like this:

    DW_AT_name      : a/test.c
    DW_AT_comp_dir  : /path/to/project/subdir1

When compiling with the -fdebug-prefix-map GCC option, the compilation
directory can be arbitrarily rewritten.  In the above example, we may
rewrite the compilation directory as follows:

    $ gcc -c a/test.c -g -fdebug-prefix-map=/path/to/project=

In this case, the corresponding debug information will look like:

    DW_AT_name      : a/test.c
    DW_AT_comp_dir  : /subdir1

This prevents GDB from finding the corresponding source code based on
the debug information alone.  In some cases, a substitute-path command
can be used to re-map a consistent prefix in the rewritten compilation
directory to the real filesystem path.  However, there may not be a
consistent prefix remaining in the debug symbols (for example in a
project that has source code in many subdirectories under the project's
root), thereby requiring multiple substitute-path rules.  In this case,
it is easier to add the missing prefix to the directory search path via
the 'directory' command.

The function find_and_open_source currently searches in:

    SEARCH_PATH/FILENAME

where SEARCH_PATH corresponds to each individual entry in the directory
search path (which is guaranteed to contain the compilation directory
from the debug information, as well as the current working directory).
FILENAME corresponds to the source filename (DW_AT_name), which may have
directory components in it.  In addition, GDB searches in:

    SEARCH_PATH/FILE_BASENAME

where FILE_BASENAME is the basename of the DW_AT_name entry.

This change modifies find_and_open_source to additionally search in:

    SEARCH_PATH/COMP_DIR/FILENAME

where COMP_DIR is the compilation directory from the debug symbols.  In
the example given earlier, running:

    (gdb) directory /path/to/project

will now allow GDB to correctly locate the source code from the debug
information.

gdb/ChangeLog:

	* 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.

gdb/doc/ChangeLog:

	* gdb.texinfo (Source Path): Additional text to better describe
	how the source path directory list is used when searching for
	source files.

gdb/testsuite/ChangeLog:

	* gdb.base/source-dir.exp: Add extra test for mapped compilation
	directory.

1 files changed, 137 insertions, 4 deletions

diff --git a/gdb/testsuite/gdb.base/source-dir.exp b/gdb/testsuite/gdb.base/source-dir.exp
index 048c0e9..25d7b07 100644
--- a/gdb/testsuite/gdb.base/source-dir.exp
+++ b/gdb/testsuite/gdb.base/source-dir.exp
@@ -15,9 +15,142 @@
 
 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
+    global decimal
+
+    # 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 \[^\n\r\]+" \
+	 "Source language is c." \
+	 "Producer is \[^\n\r\]+" \
+	 "Compiled with DWARF $decimal debugging format." \
+	 "Does not include preprocessor macro info." ] \
+	"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