[5/8] Make collect2 honour --sysroot

[Richard Sandiford <richards at transitive dot com>]

This patch adds --sysroot support to collect2.  Specifically, it makes
sure that ignore_library strips the sysroot directory from the start
of a library path before comparing it against aix_std_libs.

I haven't tried to cope with cases where there are two "/"s after
the sysroot path, or where the sysroot path ends in more "/"s than
the paths themselves.  These situations would not occur in the
automatically-generated paths we care about, and I think allowing
slash variations is conceptually a separate change.  (Slash variations
would also allow native toolchains to treat "///unix" as "/unix",
for example.)

Tested on powerpc-ibm-aix6.1 and x86_64-linux-gnu.  OK to install?

Richard


gcc/
	* collect2.c (target_system_root): New variable.
	(main): Handle --sysroot=.
	(ignore_library): Strip the sysroot from the library path.

Index: gcc/collect2.c
===================================================================
--- gcc/collect2.c	2009-06-02 13:06:05.000000000 +0100
+++ gcc/collect2.c	2009-06-02 13:06:07.000000000 +0100
@@ -217,6 +217,14 @@ static const char *ldd_file_name;	/* pat
 struct obstack temporary_obstack;
 char * temporary_firstobj;
 
+/* A string that must be prepended to a target OS path in order to find
+   it on the host system.  */
+#ifdef TARGET_SYSTEM_ROOT
+static const char *target_system_root = TARGET_SYSTEM_ROOT;
+#else
+static const char *target_system_root = "";
+#endif
+
 /* Structure to hold all the directories in which to search for files to
    execute.  */
 
@@ -1220,6 +1228,8 @@ main (int argc, char **argv)
 		  ld1--;
 		  ld2--;
 		}
+	      else if (strncmp (arg, "--sysroot=", 10) == 0)
+		target_system_root = arg + 10;
 	      break;
 	    }
 	}
@@ -2449,6 +2459,15 @@ static int ignore_library (const char *)
 ignore_library (const char *name)
 {
   const char *const *p = &aix_std_libs[0];
+  size_t length;
+
+  if (target_system_root[0] != '\0')
+    {
+      length = strlen (target_system_root);
+      if (strncmp (name, target_system_root, length) != 0)
+	return 0;
+      name += length;
+    }
   while (*p)
     if (! strcmp (name, *p++))
       return 1;