Introduction#

Variables in assembly do not exists in the same sense as they do in higher-level programming languages. This is especially true of local variabls such as those inside functions. Instead of allocating space for a particular value and having that place be "named" according to a variable, the compiler may use a combination of stack and heap allocations as well as registers to achieve behaviour resembling a variable.

That being said, there are some parallels with higher-level programming languages as well.

When manually programming assembly, it should be noted that variable names are more or less identical to addresses.

Constants#

Assembly constants cannot be changed during run-time execution. Their value is substituted at assembly-time (corresponding to compile-time substitution for constants in higher-level languages). Consequently, constants are not even assigned a location in memory, for they turn into hard-coded values.

Defining constants in assembly is done in the following way:

<NAME> equ <value>

For example,

EXAMPLE equ 0xdeadbeef

Static Initialised Data#

Static or global variables which are initialised before the programme executes are stored in the .data section. In order to define such a variable, you must give it a name, data size and value. In contrast with constants, such data can be mutated during run-time.

The following data size declarations can be used:

The syntax for declaring such variables is as follows:

<name> <dataSize> <initalValue>

For example:

byteVar db 0x1A ; byte variable

Static Uninitialised Data#

Static uninitialised data is stored in the .bss section. The syntax for allocating such variables is following:

<name> <resType> <count>

Such variables are usually allocated as chunks, hence the required count. The primary data types are as follows:

Some examples:

bArr resb 10 ; 10 element byte array  
wArr resw 50 ; 50 element word array  
dArr resd 100 ; 100 element double array  
qArr resq 200 ; 200 element quad array