- A machine code insertion can be achieved by a call to a subprogram whose
sequence_of_statements contains code_statements.
code_statement ::= qualified_expression;
- A code_statement is only allowed in the handled_sequence_of_statements of a subprogram_body. If a subprogram_body contains any code_statements, then within this subprogram_body the only allowed form of
statement is a code_statement (labeled or not), the only allowed
declarative_items are use_clauses, and no exception_handler is allowed
(comments and pragmas are allowed as usual).
Name Resolution Rules
- The qualified_expression is expected to be of any type.
- The qualified_expression shall be of a type declared in package
- A code_statement shall appear only within the scope of a with_clause that
mentions package System.Machine_Code.
- The contents of the library package System.Machine_Code (if provided) are
implementation defined. The meaning of code_statements is implementation
defined. Typically, each qualified_expression represents a machine
instruction or assembly directive.
- An implementation may place restrictions on code_statements. An
implementation is not required to provide package System.Machine_Code.
(15) An implementation may provide implementation-defined pragmas
specifying register conventions and calling conventions.
(16) Machine code functions are exempt from the rule that a return_statement is required. In fact, return_statements are forbidden, since
only code_statements are allowed.
(17) Intrinsic subprograms (see 6.3.1, ``Conformance
Rules'') can also be used to achieve machine code insertions. Interface
to assembly language can be achieved using the features in Annex
B, ``Interface to Other Languages''.
- Example of a code statement:
M : Mask;
procedure Set_Mask; pragma Inline(Set_Mask);
procedure Set_Mask is
use System.Machine_Code; -- assume ``with System.Machine_Code;'' appears somewhere above
SI_Format'(Code => SSM, B => M'Base_Reg, D => M'Disp);
-- Base_Reg and Disp are implementation-defined attributes
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
Page last generated: 95-03-12