[gcc r13-3599] gcc/file-prefix-map: Allow remapping of relative paths

[Jeff Law <law@gcc.gnu.org>]

https://gcc.gnu.org/g:e5c15eb183f17e806ad6b58c9497321ded87866f

commit r13-3599-ge5c15eb183f17e806ad6b58c9497321ded87866f
Author: Richard Purdie <richard.purdie@linuxfoundation.org>
Date:   Tue Nov 1 13:45:08 2022 -0600

    gcc/file-prefix-map: Allow remapping of relative paths
    
    Relative paths currently aren't remapped by -ffile-prefix-map and friends.
    When cross compiling with separate 'source' and 'build' directories, the same
    relative paths between directories may not be available on target as compared
    to build time.
    
    In order to be able to remap these relative build paths to paths that would
    work on target, resolve paths within the file-prefix-map function using
    realpath().
    
    This does cause a change of behaviour if users were previously relying upon
    symlinks or absolute paths not being resolved.
    
    Use basename to ensure plain filenames don't have paths added.
    
    gcc/ChangeLog:
    
            * file-prefix-map.cc (remap_filename): Allow remapping of relative paths.

Diff:
---
 gcc/file-prefix-map.cc | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/gcc/file-prefix-map.cc b/gcc/file-prefix-map.cc
index 24733f831d6..439586bd2b5 100644
--- a/gcc/file-prefix-map.cc
+++ b/gcc/file-prefix-map.cc
@@ -70,19 +70,29 @@ remap_filename (file_prefix_map *maps, const char *filename)
   file_prefix_map *map;
   char *s;
   const char *name;
+  char *realname;
   size_t name_len;
 
+  if (lbasename (filename) == filename)
+    return filename;
+
+  realname = lrealpath (filename);
+
   for (map = maps; map; map = map->next)
-    if (filename_ncmp (filename, map->old_prefix, map->old_len) == 0)
+    if (filename_ncmp (realname, map->old_prefix, map->old_len) == 0)
       break;
   if (!map)
-    return filename;
-  name = filename + map->old_len;
+    {
+      free (realname);
+      return filename;
+    }
+  name = realname + map->old_len;
   name_len = strlen (name) + 1;
 
   s = (char *) ggc_alloc_atomic (name_len + map->new_len);
   memcpy (s, map->new_prefix, map->new_len);
   memcpy (s + map->new_len, name, name_len);
+  free (realname);
   return s;
 }