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6.42 Constraints for asm
Operands
Here 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.
6.42.1 Simple Constraints | Basic use of constraints. | |
6.42.2 Multiple Alternative Constraints | When an insn has two alternative constraint-patterns. | |
6.42.3 Constraint Modifier Characters | More precise control over effects of constraints. | |
6.42.4 Constraints for Particular Machines | Special constraints for some particular machines. |
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