esp is as you say it is, the top of the stack. ebp is usually set to esp at the start of the function. Function parameters and local variables are accessed by adding and subtracting, respectively, a constant offset from ebp. All x86 calling conventions define ebp as being preserved across function calls. ebp itself … Read more
Phoronix tested the performance downside of -O2 -fno-omit-frame-pointer with x86-64 GCC 12.1 on a Zen 3 laptop CPU for multiple open-source programs, as proposed for Fedora 37. Most of them had performance regressions, a few of them very serious, although the biggest ones are probably some kind of fluke or other interaction. Geometric mean slowdown of 14% … Read more
ESP is the current stack pointer. EBP is the base pointer for the current stack frame. When you call a function, typically space is reserved on the stack for local variables. This space is usually referenced via EBP (all local variables and function parameters are a known constant offset from this register for the duration … Read more
Yes, alloca is functionally equivalent to a local variable length array, i.e. this: int arr[n]; and this: int *arr = alloca(n * sizeof(int)); both allocate space for n elements of type int on the stack. The only differences between arr in each case is that 1) one is an actual array and the other is … Read more
Maybe you’re wondering about this: push ebp mov ebp, esp sub esp, 12 These lines are known as the assembly function prologue. The first 2 instructions save the previous base pointer (ebp) and set EBP to point at that position on the stack (right below the return address). This sets up EBP as a frame … Read more
This seems to be a reliable, simple way to get the “entry” or main assembly for a web app. If you put controllers in a separate project, you may find that the base class of ApplicationInstance is not in the same assembly as your MVC project that contains the Views – but, this setup seems … Read more
There is a performance difference, especially for enter. On modern processors this decodes to some 10 to 20 µops, while the three instruction sequence is about 4 to 6, depending on the architecture. For details consult Agner Fog’s instruction tables. Additionally the enter instruction usually has a quite high latency, for example 8 clocks on … Read more
esp is the stack pointer, ebp is/was for a stack frame so that when you entered a function ebp could get a copy of esp at that point, everything on the stack before that happens, return address, passed in parameters, etc and things that are global for that function (local variables) will now be a … Read more
enter is avoided in practice as it performs quite poorly – see the answers at “enter” vs “push ebp; mov ebp, esp; sub esp, imm” and “leave” vs “mov esp, ebp; pop ebp”. There are a bunch of x86 instructions that are obsolete but are still supported for backwards compatibility reasons – enter is one … Read more
Java requires all classes that are loaded to be verified, in order to maintain the security of the sandbox and ensure that the code is safe to optimize. Note that this is done on the bytecode level, so the verification does not verify invariants of the Java language, it merely verifies that the bytecode makes … Read more