An indirect branch (also known as a computed jump, indirect jump and register-indirect jump) is a type of program control instruction present in some

machine language In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a ver ...

instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ' ...

s. Rather than specifying the address of the next instruction to

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, as in a direct

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, the

argument An argument is a statement or group of statements called premises intended to determine the degree of truth or acceptability of another statement called conclusion. Arguments can be studied from three main perspectives: the logical, the dialecti ...

specifies where the address is located. An example is 'jump indirect on the r1

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', which means that the next instruction to be executed is at the address in register r1. The address to be jumped to is not known until the instruction is executed. Indirect branches can also depend on the value of a

memory location In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers. S ...

. An indirect branch can be useful to make a

conditional branch A branch is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order. ''Branch'' (or ''branching'', ''branc ...

, especially a multiway branch. For instance, based on program input, a value could be looked up in a

jump table In computer programming, a branch table or jump table is a method of transferring program control ( branching) to another part of a program (or a different program that may have been dynamically loaded) using a table of branch or jump instruction ...

of pointers to

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for handling the various cases implied by the data value. The

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value could be added to the address of the table, with the result stored in a register. An indirect jump could then be made based on the value of that register, efficiently dispatching program control to the code appropriate to the input. In a similar manner, subroutine call instructions can be indirect, with the address of the subroutine to be called specified in memory. Function Pointers are typically implemented with indirect subroutine calls. Indirect branches were one of the attack surfaces of

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. To mitigate the attack GCC 8.1 introduced the following new options: -mindirect-branch=, -mfunction-return= and -mindirect-branch-register.

Example assembler syntax

Notes

References

Control flow Machine code {{Compu-prog-stub

Example assembler syntax

See also

Notes

References