Another approach to convert an unsigned integer to a string and write it: section .text global _start _start: mov eax, 1234567890 mov ebx, 5 add eax, ebx ; Convert EAX to ASCII and store it onto the stack sub esp, 16 ; reserve space on the stack mov ecx, 10 mov ebx, 16 .L1: xor … Read more
mov-store + mfence and xchg are both valid ways to implement a sequential-consistency store on x86. The implicit lock prefix on an xchg with memory makes it a full memory barrier, like all atomic RMW operations on x86. (x86’s memory-ordering rules essentially make that full-barrier effect the only option for any atomic RMW: it’s both … Read more
Assuming 32-bit x86, use the following function: get_eip: mov eax, [esp] ret Then, to get the value of EIP in EAX, simply: call get_eip
Excerpt from the C99 standard, normative annex F (The C++-standard does not explicitly mention this annex, though it includes all affected functions without change per reference. Also, the types have to match for compatibility.): IEC 60559 floating-point arithmetic F.1 Introduction 1 This annex specifies C language support for the IEC 60559 floating-point standard. The IEC … 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
One significant difference between LEA and ADD on x86 CPUs is the execution unit which actually performs the instruction. Modern x86 CPUs are superscalar and have multiple execution units that operate in parallel, with the pipeline feeding them somewhat like round-robin (bar stalls). Thing is, LEA is processed by (one of) the unit(s) dealing with … Read more
JE and JZ are just different names for exactly the same thing: a conditional jump when ZF (the “zero” flag) is equal to 1. (Similarly, JNE and JNZ are just different names for a conditional jump when ZF is equal to 0.) You could use them interchangeably, but you should use them depending on what … Read more
A trap is an exception in a user process. It’s caused by division by zero or invalid memory access. It’s also the usual way to invoke a kernel routine (a system call) because those run with a higher priority than user code. Handling is synchronous (so the user code is suspended and continues afterwards). In … Read more
There’s no hard and fast rule for x86 without a database as the instruction encoding is pretty complex (and the opcode itself can vary from 1 to 3 bytes). You can consult the Intel® 64 and IA-32 Architectures Software Developer’s Manual 2A document (Chapter 2: Instruction Format) to see how instructions and their operands are … Read more
Next little program was made with EMU8086 (16 bits), it captures numbers from keyboard as strings, convert them to numeric to compare, and finally it converts a number to string to display. Notice the numbers are captured with 0AH, which requieres a 3-level variable “str”. The conversion procedures that you need are at the bottom … Read more