At-T assembly language and its addressing method

Assembly language style to be divided into two main categories, one is the Intel assembly, a class is the AT-and-t assembly, respectively, Windows and Linux as the mainstream style. Since my blog is based on the recommended Linux system, I will use Linux as the main description language later.

For a brief introduction, the "#" starts with a comment line, "." Commands that start with a point are generally pseudo-directives, the "$" dollar sign is decorated immediately, and the "%" modifier registers. For example:

Addressing mode (addrsing mode) refers to the way data is organized in a fixed format: address or offset (% base or offset register,% index register, Scale factor)

the Final address = address or offset +% base address or offset Register +% index Register * Scale Factor

This string of things is basically optional, not written items are basically 0 instead, different combinations become different addressing methods, as follows:

1) Direct addressing

MOVL ADDRESS,%eax

Address is actually the equivalent of "address or offset" in the addresses, anyway, is a number.

2) Register addressing

In fact, the above example also includes register addressing, as the name implies%eax is register addressing, representing the register itself to write or read out.

3) Immediate Addressing

MOVL,%EBX

I have always felt that immediate addressing is not an address, anyway it means to write 2 this number to the%EAX register, which is immediately addressed, in fact, the immediate number.

4) Indirect addressing

MOVL (%eax),%EBX

(%EAX) is an indirection, meaning access to the address represented by the value in the EAX register. Equivalent to the% base or offset register in the general formula.

5) Index Addressing (variable addressing)

Movl 0xffff0000 (,%eax,4),%EBX

0xffff0000 (,%eax,4) is index addressing, which means starting with the 0xffff0000 address, plus%EAX * 4 as the final address of the index. Please match the general formula above for yourself.

6) addressing the base address

MOVL 4 (%eax),%EBX

4 (%EAX) is the base address, meaning that the value in the EAX register is used as the base, plus 4 to get the final addresses. can also be matched to the general formula above, and this is a very common way of addressing.

Https://www.cnblogs.com/orlion/p/5765339.html

Http://blog.csdn.net/column/details/linuxcode.html

http://blog.csdn.net/jnu_simba/article/details/11747901

At-T assembly language and its addressing method