Next: Asm Labels, Previous: Extended Asm, Up: Using Assembly Language with C [Contents][Index]
asm OperandsHere are specific details on what constraint letters you can use with
asm operands.
Constraints can say whether
an operand may be in a register, and which kinds of register; whether the
operand can be a memory reference, and which kinds of address; whether the
operand may be an immediate constant, and which possible values it may
have. Constraints can also require two operands to match.
Side-effects aren’t allowed in operands of inline asm, unless
‘<’ or ‘>’ constraints are used, because there is no guarantee
that the side-effects will happen exactly once in an instruction that can update
the addressing register.
| • Simple Constraints: | Basic use of constraints. | |
| • Multi-Alternative: | When an insn has two alternative constraint-patterns. | |
| • Modifiers: | More precise control over effects of constraints. | |
| • Machine Constraints: | Special constraints for some particular machines. |