Lea assembly instruction

As others have pointed out, LEA (load effective address) is often used as a "trick" to do certain computations, but that's not its primary purpose. The x86 instruction set was designed to support high-level languages like Pascal and C, where arrays—especially arrays of ints or small structs—are common. Consider, for example, a struct representing (x, y) coordinates:

struct Point
{
     int xcoord;
     int ycoord;
};

Now imagine a statement like:

int y = points[i].ycoord;

where points[] is an array of Point. Assuming the base of the array is already in EBX, and variable i is in EAX, and xcoord and ycoord are each 32 bits (so ycoord is at offset 4 bytes in the struct), this statement can be compiled to:

MOV EDX, [EBX + 8*EAX + 4]    ; right side is "effective address"

which will land y in EDX. The scale factor of 8 is because each Point is 8 bytes in size. Now consider the same expression used with the "address of" operator &:

int *p = &points[i].ycoord;

In this case, you don't want the value of ycoord, but its address. That's where LEA (load effective address) comes in. Instead of a MOV, the compiler can generate

LEA ESI, [EBX + 8*EAX + 4]

which will load the address in ESI.

movl 8(%ebp), %edx

is in "AT&T Syntax"; in this syntax, the source comes first and the destination second. So yes, your belief is correct. Most documentation uses the "Intel Syntax", which has the reverse ordering. This is a source of considerable confusion for people new to x86 assembly.

In Intel Syntax, your instruction would be written:

mov edx, [ebp + 8]

Note the absence of % before the register names, and the use of square brackets instead of parentheses for the address, and the lack of an l suffix on the instruction. These are dead giveaways to know which form of assembly you are looking at.