This question already has answers here: Closed 9 years ago. Possible Duplicate: x86 Assembly – ‘testl’ eax against eax? I’m very very new to assembly language programming, and I’m currently trying to read the assembly language generated from a binary. I’ve run across test %eax,%eax or test %rdi, %rdi, etc. etc. I’m very confused as … Read more
I tried to compare the performance of inline assembly language and C++ code, so I wrote a function that add two arrays of size 2000 for 100000 times. Here’s the code: #define TIMES 100000 void calcuC(int *x,int *y,int length) { for(int i = 0; i < TIMES; i++) { for(int j = 0; j < … Read more
I’m doing some assembly-level debugging in GDB. Is there a way to get GDB to show me the current assembly instruction in the same way that it shows the current source line? The default output after every command looks like this: 0x0001433f 990 Foo::bar(p); This gives me the address of the current instruction, but I … Read more
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I’ve been contemplating how to protect my C/C++ code from disassembly and reverse engineering. Normally I would never condone this behavior myself in my code; however the current protocol I’ve been working on must not ever be inspected or understandable, for the security of various people. Now this is a new subject to me, and … Read more
Background: While optimizing some Pascal code with embedded assembly language, I noticed an unnecessary MOV instruction, and removed it. To my surprise, removing the un-necessary instruction caused my program to slow down. I found that adding arbitrary, useless MOV instructions increased performance even further. The effect is erratic, and changes based on execution order: the … Read more
I’ve been reading about div and mul assembly operations, and I decided to see them in action by writing a simple program in C: File division.c #include <stdlib.h> #include <stdio.h> int main() { size_t i = 9; size_t j = i / 5; printf(“%zu\n”,j); return 0; } And then generating assembly language code with: gcc … Read more
Using this example coming from wikipedia, in which DrawSquare() calls DrawLine(), (Note that this diagram has high addresses at the bottom and low addresses at the top.) Could anyone explain me what ebp and esp are in this context? From what I see, I’d say the stack pointer points always to the top of the … Read more
What is the difference between object code, machine code and assembly code? Can you give a visual example of their difference? 10 Answers 10
In order to mitigate against kernel or cross-process memory disclosure (the Spectre attack), the Linux kernel1 will be compiled with a new option, -mindirect-branch=thunk-extern introduced to gcc to perform indirect calls through a so-called retpoline. This appears to be a newly invented term as a Google search turns up only very recent use (generally all … Read more