[RFA] arm-tdep.c: deal with failed memory read

[Elena Zannoni <ezannoni at cygnus dot com>]

If, upon initial connection to a remote ARM target, the contents of
r11 (which is the Frame Pointer) are junk, a memory read from
arm_scan_prologue can fail and abort the whole connection to the
remote target. There are several ways to fix this, and probably the
most correct one is to teach gdb to do the initial connection in 2
separate steps. First connect and declare that successful or not, then
start reading memory if the connection was established.

This patch is just a band-aid to allow intercepting bad memory reads
and not aborting the connection.  It has been in our internal
repository for a couple of months now. It is by no means a complete
solution, but it improves things a bit.

OK?

Elena


2001-11-21  Elena Zannoni  <ezannoni@redhat.com>

        * corefile.c (do_captured_read_memory_integer,
        gdb_read_memory_integer): New functions.
        * gdbcore.h (gdb_read_memory_integer): Export.
        * arm-tdep.c (arm_scan_prologue): Use gdb_read_memory_integer,
        to read the frame value, to capture calls to error().

Index: arm-tdep.c
===================================================================
RCS file: /cvs/uberbaum/gdb/arm-tdep.c,v
retrieving revision 1.17
diff -u -p -r1.17 arm-tdep.c
--- arm-tdep.c	2001/11/14 08:18:32	1.17
+++ arm-tdep.c	2001/11/22 00:08:28
@@ -717,6 +717,7 @@ static void
 arm_scan_prologue (struct frame_info *fi)
 {
   int regno, sp_offset, fp_offset;
+  LONGEST return_value;
   CORE_ADDR prologue_start, prologue_end, current_pc;
 
   /* Check if this function is already in the cache of frame information. */
@@ -781,9 +782,13 @@ arm_scan_prologue (struct frame_info *fi
     {
       /* Get address of the stmfd in the prologue of the callee; the saved
          PC is the address of the stmfd + 8.  */
-      prologue_start = ADDR_BITS_REMOVE (read_memory_integer (fi->frame, 4))
-	- 8;
-      prologue_end = prologue_start + 64;	/* See above. */
+      if (!gdb_read_memory_integer (fi->frame, 4,  &return_value))
+	return;
+      else
+	{
+	  prologue_start = ADDR_BITS_REMOVE (return_value) - 8;
+	  prologue_end = prologue_start + 64;	/* See above. */
+	}
     }
 
   /* Now search the prologue looking for instructions that set up the
Index: corefile.c
===================================================================
RCS file: /cvs/uberbaum/gdb/corefile.c,v
retrieving revision 1.15
diff -u -p -r1.15 corefile.c
--- corefile.c	2001/11/12 21:08:04	1.15
+++ corefile.c	2001/11/22 00:08:50
@@ -262,6 +262,41 @@ dis_asm_print_address (bfd_vma addr, str
 
 /* Read an integer from debugged memory, given address and number of bytes.  */
 
+struct captured_read_memory_integer_arguments
+{
+  CORE_ADDR memaddr;
+  int len;
+  LONGEST result;
+};
+
+static int
+do_captured_read_memory_integer (void *data)
+{
+  struct captured_read_memory_integer_arguments *args = (struct captured_read_memory_integer_arguments*) data
;
+  CORE_ADDR memaddr = args->memaddr;
+  int len = args->len;
+
+  args->result = read_memory_integer (memaddr, len);
+
+  return 0;
+}
+
+int
+gdb_read_memory_integer (CORE_ADDR memaddr, int len, LONGEST *return_value)
+{
+  int status;
+  struct captured_read_memory_integer_arguments args;
+  args.memaddr = memaddr;
+  args.len = len;
+
+  status = catch_errors (do_captured_read_memory_integer, &args,
+			 "", RETURN_MASK_ALL);
+  if (!status)
+    *return_value = args.result;
+
+  return status;
+}
+
 LONGEST
 read_memory_integer (CORE_ADDR memaddr, int len)
 {
Index: gdbcore.h
===================================================================
RCS file: /cvs/uberbaum/gdb/gdbcore.h,v
retrieving revision 1.8
diff -u -p -r1.8 gdbcore.h
--- gdbcore.h	2001/11/12 21:08:04	1.8
+++ gdbcore.h	2001/11/22 00:09:12
@@ -55,6 +55,7 @@ extern void read_memory (CORE_ADDR memad
    bytes.  */
 
 extern LONGEST read_memory_integer (CORE_ADDR memaddr, int len);
+extern int gdb_read_memory_integer (CORE_ADDR memaddr, int len, LONGEST *return_value);
 
 /* Read an unsigned integer from debugged memory, given address and
    number of bytes.  */