CODEWITHSUNDEEP
assemblysyntaxx86memory-addressaddressing-mode
Tony92
Tony92

Reputation: 105

Why are Square Brackets used in LEA?

In assembly, the square brackets [] seem to have the same meaning as * in C programming language. They are used to dereference a pointer. Dereferencing a pointer means going to refer to a specific memory location to read or write it.

So, it is quite logical to use square brackets in the case of a MOV. But what is the logical reason why they also use it for LEA?

LEA EAX, [EBP -4], looks like dereferencing a pointer, EBP - 4, to refer to the pointed memory location but it will not read the value contained in the location but rather the address.

I'm a little confused about this. Could you give me the right way to think about this?
Does LEA have any connection with the concept of dereferencing? Clearly not intended as a memory reading, but mostly as referring to a location of memory not for its value, but for its address. I wouldn't want this to become a philosophical question.

Upvotes: 4

Views: 1310

Answers (1)

Erik Eidt
Erik Eidt

Reputation: 26766

The LEA instruction is designed to look like a memory access instruction — so can perform all the addressing modes.  The difference, of course, as you're noting is that LEA loads the "effective address" rather than a memory value from that location.

Thus, LEA is similar to memory access operations, but specifically, in C terms, is taking the address — so like &a[i] in C.  Like in C with &, the result of LEA is always a pointer sized value rather than with real accesses where we can fetch/store a byte, word, etc..

Upvotes: 5

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