[RFA][1/5] New port: Cell BE SPU (dwarf2loc.c fix)

Ulrich Weigand
2006-11-11T18:37:50Z

Hello,

this fixes a problem in dwarf2loc.c that triggers for the SPU port.

The code in dwarf_expr_read_reg currently expects that in order to
retrieve an address value from a register, it's OK to assume the
address can always be extracted using extract_unsigned_integer
on the full size of the register.

This fails on the SPU, because all registers are 16 bytes wide, and
a pointer is represented by simply using the uppermost 4 bytes and
ignoring the contents of the remaining 12 bytes. I would assume
that there's also other architectures where the assumption in
dwarf_expr_read_reg might fail, e.g. due to sign extension issues
or other required fiddling.

So, to fix this I thought that we already *know* how to extract
values of a certain type from a register: value_from_register does
just that, and provides all sorts of configurability for the back
end to have it just do the right thing. Since the value retrieved
by dwarf_expr_read_reg is always a pointer to some data object
(normally on the stack), it should be OK to get it by using
value_from_register (builtin_type_void_data_ptr, ...).

This is what the patch below does, and it works fine on SPU.
Additionally tested without regressions on s390-ibm-linux and
s390x-ibm-linux.

OK?

Bye,
Ulrich

* dwarf2loc.c (dwarf_expr_read_reg): Use value_from_register to
retrieve address from register.

diff -ur gdb-orig/gdb/dwarf2loc.c gdb-head/gdb/dwarf2loc.c
--- gdb-orig/gdb/dwarf2loc.c 2006-11-10 03:00:22.000000000 +0100
+++ gdb-head/gdb/dwarf2loc.c 2006-11-11 18:16:58.663849888 +0100
@@ -115,23 +115,23 @@
/* Helper functions for dwarf2_evaluate_loc_desc. */

/* Using the frame specified in BATON, return the value of register
- REGNUM, treated as an unsigned integer. */
+ REGNUM, treated as a pointer. */
static CORE_ADDR
dwarf_expr_read_reg (void *baton, int dwarf_regnum)
{
struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
+ struct value *value;
CORE_ADDR result;
- gdb_byte *buf;
- int regnum, regsize;
+ int regnum;

regnum = DWARF2_REG_TO_REGNUM (dwarf_regnum);
- regsize = register_size (current_gdbarch, regnum);
- buf = alloca (regsize);

- frame_register_read (debaton->frame, regnum, buf);
- /* 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, regsize);
+ value = value_from_register (builtin_type_void_data_ptr,
+ regnum, debaton->frame);
+
+ result = value_as_address (value);
+ release_value (value);
+ value_free (value);

return result;
}