[PATCH] PIE support for OpenBSD

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

Just a matter of getting the right info out of the auxv vector, and I
added support to the OpenBSD kernel for that a while ago.  Needs its
own function to parse the values since default_auxv_parse is
Linux-specific (and therefore not standards compliant on LP64
platforms).  It can be argued that the parsing routine should really
live in the architecture vector.  But 32x64-bit cross-debugging
muddies the waters here.

For now this is OpenBSD-specific, but FreeBSD and NetBSD might
implement the PIOD_READ_AUXV request at some point too.

ok?


2011-12-17  Mark Kettenis  <kettenis@gnu.org>
 
	* inf-ptrace.c [PT_IO && PIOD_READ_AUXV]
	(inf_ptrace_xfer_partial): Implement TARGET_OBJECT_AUXV.
	(inf_ptrace_auxv_parse): New function.
	(inf_ptrace_target): Initialize to_auxv_parse field.

Index: inf-ptrace.c
===================================================================
RCS file: /cvs/src/src/gdb/inf-ptrace.c,v
retrieving revision 1.75
diff -u -p -r1.75 inf-ptrace.c
--- inf-ptrace.c	22 Sep 2011 10:22:28 -0000	1.75
+++ inf-ptrace.c	17 Dec 2011 20:58:40 -0000
@@ -582,6 +582,23 @@ inf_ptrace_xfer_partial (struct target_o
       return -1;
 
     case TARGET_OBJECT_AUXV:
+#if defined (PT_IO) && defined (PIOD_READ_AUXV)
+      {
+	struct ptrace_io_desc piod;
+
+	if (writebuf)
+		return -1;
+	piod.piod_op = PIOD_READ_AUXV;
+	piod.piod_addr = readbuf;
+	piod.piod_offs = (void *) (long) offset;
+	piod.piod_len = len;
+
+	errno = 0;
+	if (ptrace (PT_IO, pid, (caddr_t)&piod, 0) == 0)
+	  /* Return the actual number of bytes read or written.  */
+	  return piod.piod_len;
+      }
+#endif
       return -1;
 
     case TARGET_OBJECT_WCOOKIE:
@@ -619,6 +636,41 @@ inf_ptrace_pid_to_str (struct target_ops
   return normal_pid_to_str (ptid);
 }
 
+#if defined (PT_IO) && defined (PIOD_READ_AUXV)
+
+/* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
+   Return 0 if *READPTR is already at the end of the buffer.
+   Return -1 if there is insufficient buffer for a whole entry.
+   Return 1 if an entry was read into *TYPEP and *VALP.  */
+
+static int
+inf_ptrace_auxv_parse (struct target_ops *ops, gdb_byte **readptr,
+		       gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
+{
+  struct type *int_type = builtin_type (target_gdbarch)->builtin_int;
+  struct type *ptr_type = builtin_type (target_gdbarch)->builtin_data_ptr;
+  const int sizeof_auxv_type = TYPE_LENGTH (int_type);
+  const int sizeof_auxv_val = TYPE_LENGTH (ptr_type);
+  enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch);
+  gdb_byte *ptr = *readptr;
+
+  if (endptr == ptr)
+    return 0;
+
+  if (endptr - ptr < 2 * sizeof_auxv_val)
+    return -1;
+
+  *typep = extract_unsigned_integer (ptr, sizeof_auxv_type, byte_order);
+  ptr += sizeof_auxv_val;	/* Alignment.  */
+  *valp = extract_unsigned_integer (ptr, sizeof_auxv_val, byte_order);
+  ptr += sizeof_auxv_val;
+
+  *readptr = ptr;
+  return 1;
+}
+
+#endif
+
 /* Create a prototype ptrace target.  The client can override it with
    local methods.  */
 
@@ -644,6 +696,9 @@ inf_ptrace_target (void)
   t->to_pid_to_str = inf_ptrace_pid_to_str;
   t->to_stop = inf_ptrace_stop;
   t->to_xfer_partial = inf_ptrace_xfer_partial;
+#if defined (PT_IO) && defined (PIOD_READ_AUXV)
+  t->to_auxv_parse = inf_ptrace_auxv_parse;
+#endif
 
   return t;
 }