Re: [RFC] dwarf2_read_address(): sign extend as appropriate

Kevin Buettner
2007-04-27T21:10:30Z

I decided to give the `value_as_address' approach a try. It worked
as expected when I tried running it against a MIPS target.

Comments?

* dwarf2expr.c (unsigned_address_type): Add forward declaration.
(dwarf2_read_address): Sign extend return address as required by
target architecture.

Index: dwarf2expr.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
retrieving revision 1.19
diff -u -p -r1.19 dwarf2expr.c
--- dwarf2expr.c 9 Jan 2007 17:58:50 -0000 1.19
+++ dwarf2expr.c 27 Apr 2007 21:07:10 -0000
@@ -33,6 +33,7 @@

static void execute_stack_op (struct dwarf_expr_context *,
gdb_byte *, gdb_byte *);
+static struct type *unsigned_address_type (void);

/* Create a new context for the expression evaluator. */

@@ -205,9 +206,42 @@ dwarf2_read_address (gdb_byte *buf, gdb_
error (_("dwarf2_read_address: Corrupted DWARF expression."));

*bytes_read = TARGET_ADDR_BIT / TARGET_CHAR_BIT;
- /* NOTE: cagney/2003-05-22: This extract is assuming that a DWARF 2
- address is always unsigned. That may or may not be true. */
- result = extract_unsigned_integer (buf, TARGET_ADDR_BIT / TARGET_CHAR_BIT);
+
+ /* For most architectures, calling extract_unsigned_integer() alone
+ is sufficient for extracting an address. However, some
+ architectures (e.g. MIPS) use signed addresses and using
+ extract_unsigned_integer() will not produce a correct
+ result. Turning the unsigned integer into a value and then
+ decomposing that value as an address will cause
+ gdbarch_integer_to_address() to be invoked for those
+ architectures which require it. Thus, using value_as_address()
+ will produce the correct result for both types of architectures.
+
+ One concern regarding the use of values for this purpose is
+ efficiency. Obviously, these extra calls will take more time to
+ execute and creating a value takes more space, space which will
+ have to be garbage collected at a later time. If constructing
+ and then decomposing a value for this purpose proves to be too
+ inefficient, then gdbarch_integer_to_address() can be called
+ directly. This could be done as follows:
+
+ if (gdbarch_integer_to_address_p (current_gdbarch))
+ result = gdbarch_integer_to_address (current_gdbarch,
+ unsigned_address_type (), buf);
+ else
+ result = extract_unsigned_integer
+ (buf, TARGET_ADDR_BIT / TARGET_CHAR_BIT);
+
+ The use of `unsigned_address_type' in the code below (or in the
+ suggested replacement code above) refers to the type of buf and
+ has no bearing on the signedness of the address being returned. */
+
+ result = value_as_address (value_from_longest
+ (unsigned_address_type (),
+ extract_unsigned_integer
+ (buf,
+ TARGET_ADDR_BIT / TARGET_CHAR_BIT)));
+
return result;
}