sh: Add support for DWARF GNU extensions

Also, remove the "fix" to DW_CFA_def_cfa_register where we reset the
frame's cfa_offset to 0. This action is incorrect when handling
DW_CFA_def_cfa_register as the DWARF spec specifically states that the
previous contents of cfa_offset should be used with the new
register. The reason that I thought cfa_offset should be reset to 0 was
because it was being assigned a bogus value prior to executing the
DW_CFA_def_cfa_register op. It turns out that the bogus cfa_offset value
came from interpreting .cfi_escape pseudo-ops (those used by the GNU
extensions) as CFA_DW_def_cfa ops.
Signed-off-by: Matt Fleming <matt@console-pimps.org>

arch/sh/include/asm/dwarf.h

@@ -340,6 +340,10 @@ struct dwarf_stack {
 #define DW_CFA_lo_user		0x1c
 #define DW_CFA_hi_user		0x3f
 
+/* GNU extension opcodes  */
+#define DW_CFA_GNU_args_size	0x2e
+#define DW_CFA_GNU_negative_offset_extended 0x2f
+
 /*
  * Some call frame instructions encode their operands in the opcode. We
  * need some helper functions to extract both the opcode and operands

arch/sh/kernel/dwarf.c

@@ -429,7 +429,6 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 			count = dwarf_read_uleb128(current_insn,
 						   &frame->cfa_register);
 			current_insn += count;
-			frame->cfa_offset = 0;
 			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 			break;
 		case DW_CFA_def_cfa_offset:
@@ -465,6 +464,19 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 			frame->regs[reg].flags |= DWARF_REG_OFFSET;
 			frame->regs[reg].addr = offset;
 			break;
+		case DW_CFA_GNU_args_size:
+			count = dwarf_read_uleb128(current_insn, &offset);
+			current_insn += count;
+			break;
+		case DW_CFA_GNU_negative_offset_extended:
+			count = dwarf_read_uleb128(current_insn, &reg);
+			current_insn += count;
+			count = dwarf_read_uleb128(current_insn, &offset);
+			offset *= cie->data_alignment_factor;
+			dwarf_frame_alloc_regs(frame, reg);
+			frame->regs[reg].flags |= DWARF_REG_OFFSET;
+			frame->regs[reg].addr = -offset;
+			break;
 		default:
 			pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 			break;