static int dwarf_cfa_execute_insns()

in kernel/dwarf.c [396:550]

• 135 lines of code
• 20 McCabe index (conditional complexity)

static int dwarf_cfa_execute_insns(unsigned char *insn_start,
				   unsigned char *insn_end,
				   struct dwarf_cie *cie,
				   struct dwarf_fde *fde,
				   struct dwarf_frame *frame,
				   unsigned long pc)
{
	unsigned char insn;
	unsigned char *current_insn;
	unsigned int count, delta, reg, expr_len, offset;
	struct dwarf_reg *regp;

	current_insn = insn_start;

	while (current_insn < insn_end && frame->pc <= pc) {
		insn = __raw_readb(current_insn++);

		/*
		 * Firstly, handle the opcodes that embed their operands
		 * in the instructions.
		 */
		switch (DW_CFA_opcode(insn)) {
		case DW_CFA_advance_loc:
			delta = DW_CFA_operand(insn);
			delta *= cie->code_alignment_factor;
			frame->pc += delta;
			continue;
			/* NOTREACHED */
		case DW_CFA_offset:
			reg = DW_CFA_operand(insn);
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->addr = offset;
			regp->flags |= DWARF_REG_OFFSET;
			continue;
			/* NOTREACHED */
		case DW_CFA_restore:
			reg = DW_CFA_operand(insn);
			continue;
			/* NOTREACHED */
		}

		/*
		 * Secondly, handle the opcodes that don't embed their
		 * operands in the instruction.
		 */
		switch (insn) {
		case DW_CFA_nop:
			continue;
		case DW_CFA_advance_loc1:
			delta = *current_insn++;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_advance_loc2:
			delta = get_unaligned((u16 *)current_insn);
			current_insn += 2;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_advance_loc4:
			delta = get_unaligned((u32 *)current_insn);
			current_insn += 4;
			frame->pc += delta * cie->code_alignment_factor;
			break;
		case DW_CFA_offset_extended:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			break;
		case DW_CFA_restore_extended:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			break;
		case DW_CFA_undefined:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_UNDEFINED;
			break;
		case DW_CFA_def_cfa:
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_register);
			current_insn += count;
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_offset);
			current_insn += count;

			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
			break;
		case DW_CFA_def_cfa_register:
			count = dwarf_read_uleb128(current_insn,
						   &frame->cfa_register);
			current_insn += count;
			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
			break;
		case DW_CFA_def_cfa_offset:
			count = dwarf_read_uleb128(current_insn, &offset);
			current_insn += count;
			frame->cfa_offset = offset;
			break;
		case DW_CFA_def_cfa_expression:
			count = dwarf_read_uleb128(current_insn, &expr_len);
			current_insn += count;

			frame->cfa_expr = current_insn;
			frame->cfa_expr_len = expr_len;
			current_insn += expr_len;

			frame->flags |= DWARF_FRAME_CFA_REG_EXP;
			break;
		case DW_CFA_offset_extended_sf:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_leb128(current_insn, &offset);
			current_insn += count;
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_REG_OFFSET;
			regp->addr = offset;
			break;
		case DW_CFA_val_offset:
			count = dwarf_read_uleb128(current_insn, &reg);
			current_insn += count;
			count = dwarf_read_leb128(current_insn, &offset);
			offset *= cie->data_alignment_factor;
			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_VAL_OFFSET;
			regp->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;

			regp = dwarf_frame_alloc_reg(frame, reg);
			regp->flags |= DWARF_REG_OFFSET;
			regp->addr = -offset;
			break;
		default:
			pr_debug("unhandled DWARF instruction 0x%x\n", insn);
			UNWINDER_BUG();
			break;
		}
	}

	return 0;
}