Nov 11, 2022 · Registers can be used in your software directly with instructions such as mov, add or cmp. The leading e stands for e xtended and means that your register is 32 bits wide. On the other hand, 64-bit registers begin with r. These registers are not always used for the purposes illustrated below.

%eax is a 32-bit register (just like %al is 8-bit, %ax is 16-bit and %rax is 64-bit). While %rsp in (%rsp) is 64-bit, the expression (%rsp) is a move to the memory location held in %rsp, and as such has no register size associated to it. So the mov (e) is 32-bit, and the suffix is l.

Modern (i.e 386 and beyond) x86 processors have eight 32-bit general purpose registers, as depicted in Figure 1. The register names are mostly historical. For example, EAX used to be called the accumulator since it was used by a number of arithmetic operations, and ECX was known as the counter since it was used to hold a loop index.

eax is the 32-bit, "int" size register. It was added in 1985 during the transition to 32-bit processors with the 80386 CPU. I'm in the habit of using this register size, since they also work in 32 bit mode, although I'm trying to use the longer rax registers for everything.

May 4, 2017 · simply copies the value in ebx into eax. In a pseudo-C notation, this would be: eax = ebx. Whereas this: dereferences the contents of ebx and stores the pointed-to value in eax. In a pseudo-C notation, this would be: eax = *ebx. Finally, this: stores the value in ebx into the memory location pointed to by eax.

The eax register receives function return values if the result is 32 bits or smaller. If the result is 64 bits, then the result is stored in the edx:eax pair. The following is a list of calling conventions used on the x86 architecture:

In 1985, Intel launched the i386, which started the x86 line of processors. Once again the register size doubled. The 32-bit accumulator register was named ‘Extended AX’ (EAX). The AX, AH, and AL sub-registers are all accessible within EAX:

Jan 1, 2024 · It is also possible to address the first four registers (AX, CX, DX and BX) in their size of 16-bit as two 8-bit halves. The least significant byte (LSB), or low half, is identified by replacing the 'X' with an 'L'. The most significant byte (MSB), or high half, uses an 'H' instead.

Nov 30, 2015 · EAX generally contains the return of a function. If you see the EAX register just after a function call, chances are that EAX contains the return value of the function. EAX and EDX are always implied in multiplication and division instructions; EAX can also be used as a temporary CPU memory for additions:

Modern (i.e 386 and beyond) x86 processors have 8 32-bit general purpose registers, as depicted in Figure 1. The register names are mostly historical in nature. For example, EAX used to be called the “accumulator” since it was used by a number of arithmetic operations, and ECX was known as the “counter” since it was used to hold a loop index.