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ret

return from subroutine

Jasmin Syntax

     ret <varnum> or     wide     ret <varnum> 

In the first form, <varnum> is an unsigned integer in the range 0 to 0xFF. In the second (wide) form, <varnum> is an unsigned integer in the range 0 to 0xFFFF.

Stack

Before	After
...	...

Description

ret is used to return from a subroutine that was invoked by jsr or jsr_w. It takes a single parameter, <varnum>, an unsigned integer which local variable is holding the returnAddress for this subroutine. Execution continues at the address stored in that local variable.

Return addresses are left on the stack by the jsr and jsr_w instructions. Methods are expected to immediately store the return address in a local variable, ready for use with ret.

Example

 ; This example method uses a PrintMe subroutine to invoke the System.out.println() method. .method usingSubroutine()V     ldc "Message 1"     jsr PrintMe          ; print "Message 1"     ldc "Message 2"     jsr PrintMe          ; print "Message 2"     ldc "Message 3"     jsr PrintMe          ; print "Message 3"     return   ; now return from usingSubroutine ; define the PrintMe subroutine ... PrintMe:            astore_1            ; store return-address in local variable 1     ; call System.out.println()     getstatic java/lang/System/out Ljava/io/PrintStream;     invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V     ret 1               ; return to the return-address in local variable 1 .end method 

Bytecode

For local variable numbers in the range 0-255, use:

Type	Description
u1	ret opcode = 0xA9 (169)
u1	<varnum>

There is also a wide format for this instruction, which supports access to all local variables from 0 to 65535:

Type	Description
u1	wide opcode = 0xC4 (196)
u1	ret opcode = 0xA9 (169)
u2	<varnum>

See Also

jsr, jsr_w, goto, goto_w, wide

Notes

The assymetry between jsr (which pushes a returnAddress onto the stack) and ret (which gets the returnAddress from a local variable) is intentional - the bytecode verifier relies on this structure (see Chapter 5) .

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Java Virtual Machine, by Jon Meyer and Troy Downing, O'Reilly Associates