What does the code below exactly mean?

lea rdx,qword ptr ss:[rbp+50]

I have difficulty in rbp+50. Is rbp the base pointer in the 64 bit CPU architecture? What is the base pointer refering to? how can I find out the value at rbp+50? what does ss mean? what does qword mean? I totally confused with these terms.


1 Answer 1


The code means rdx = rbp + 50.

For the explanation, we'll go bottom up...

qword is 8-bytes (64 bits). It stands for quad-word, same as dword stands for double-word. It is the size of every rXX register. The qword ptr means that we are accessing a qword sized memory block (as oppised to a byte, word or dword).

ss stands for stack-segment. However, in non 16-bit systems all segments are usually mapped to 0. It is probably shown in the code as an artifact of the dis-assembly as the rbp register is used to point into the stack.

The lea commands mean load-effective-address. It does not take the value at the given address, but rather the address itself. So in pseudo code we can rewrite the entire thing as rdx = rbp + 50.

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