Dec 132023

[Raymond Chen] wondered why the x86 ENTER instruction had a strange second parameter that seems to always be set to zero. If you’ve ever wondered, [Raymond] explains what he learned in a recent blog post.
If you’ve ever taken apart the output of a C compiler or written assembly programs,  you probably know that ENTER is supposed to set up a new stack frame. Presumably, you are in a subroutine, and some arguments were pushed on the stack for you. The instruction puts the pointer to those arguments in EBP and then adjusts the stack pointer to account for your local variables. That local variable size is the first argument to ENTER.
The reason you rarely see it…

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