Re: [PATCH] make ggc pick up comp_dir_string() cache value. (dwarf2out.c)

[Otto, Thomas]

> > And I still think this function and the static variable which never changes
> > once set does not require any GC. Just setting the cached_wd variable to 
> > the unchanged pointer from get_src_pwd() or allocating one in the function 
> > itself is enough. This solves the problem and relieves the GC from the task 
> > of 
> > watching over a variable which lives forever anyhow.
> 
> Yes, that works as well then.

Ok, see the attached patch.

Regards,

Thomas

2019-03-22  Thomas Otto  <thomas.o...@pdv-fs.de>

	* dwarf2out.c (comp_dir_string): cached_wd could be set to both a
	heap string and a gc string, but since this variable is unknown to
	ggc the gc string might get reused and corrupted. Fixed by always
	using a heap string.

--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -20702,7 +20702,7 @@ static const char *
 comp_dir_string (void)
 {
   const char *wd;
-  char *wd1;
+  char *wd_plus_sep = NULL;
   static const char *cached_wd = NULL;
 
   if (cached_wd != NULL)
@@ -20714,17 +20714,26 @@ comp_dir_string (void)
 
   if (DWARF2_DIR_SHOULD_END_WITH_SEPARATOR)
     {
-      int wdlen;
-
-      wdlen = strlen (wd);
-      wd1 = ggc_vec_alloc<char> (wdlen + 2);
-      strcpy (wd1, wd);
-      wd1 [wdlen] = DIR_SEPARATOR;
-      wd1 [wdlen + 1] = 0;
-      wd = wd1;
+      size_t wdlen = strlen (wd);
+      wd_plus_sep = XNEWVEC (char, wdlen + 2);
+      strcpy (wd_plus_sep, wd);
+      wd_plus_sep [wdlen] = DIR_SEPARATOR;
+      wd_plus_sep [wdlen + 1] = 0;
+      wd = wd_plus_sep;
     }
 
   cached_wd = remap_debug_filename (wd);
+
+  /* remap_debug_filename can just pass through wd or return a new gc string.
+     These two types can't be both stored in a GTY(())-tagged string, but since
+     the cached value lives forever just copy it if needed.  */
+  if (cached_wd != wd)
+    {
+      cached_wd = xstrdup (cached_wd);
+      if (DWARF2_DIR_SHOULD_END_WITH_SEPARATOR && wd_plus_sep != NULL)
+        free (wd_plus_sep);
+    }
+
   return cached_wd;
 }