MASM is Microsoft's assembler, an abbreviation for "Macro Assembler." However, many people use it as an acronym for "Microsoft Assembler," and the difference isn't a problem at all. Many of these assemblers (or new versions of them) can handle amd64/x86_64/EMT64 code as well, although this wikibook will focus primarily on 32 bit (x86/IA-32) code examples. Intel Syntax Assemblers īecause of the pervasiveness of Intel-based IA-32 microprocessors in the home PC market, the majority of assembly work done (and the majority of assembly work considered in this wikibook) is x86-based. The code will be accurate, but more difficult to read.Ĭompilers, as we will see later, cause even more information to be lost, and decompiling is often so difficult and convoluted as to become nearly impossible to do accurately. When you disassemble the code, the instructions will be the same, but all the other helpful information will be lost. Second, textual information from the assembly source code file, such as variable names, label names, and code comments are all destroyed during assembly.
Notice that you can disassemble raw data, but the resultant assembly code will be nonsensical. This means that it can be difficult to determine which parts of the program are actually instructions. First and foremost, program data is stored in the same raw binary format as the machine code instructions. Some information about the program is lost during the assembly process. Some assemblers have high-level capabilities in the form of Macros. The machine code that comes out of an assembler is equivalent to the assembly instructions that go into the assembler.
They can also translate named variables into hard-coded memory addresses and labels into their relative code addresses.Īssemblers, in general, do not perform code optimization. We will introduce assemblers here, and talk about disassembly later.Īssembler Concepts Īssemblers, on a most basic level, translate assembly instructions into machine code with a one to one correspondence. However, disassembly has some other difficulties which cannot be accounted for using simple code-word lookups.
Assembly instructions and machine code words have a one-to-one correspondence, so each machine code word will exactly map to one assembly instruction. Assemblers rarely optimize beyond choosing the shortest form of an instruction or filling delay slots.īecause assembly is such a simple process, disassembly can often be just as simple. Assemblers are significantly simpler than compilers, and are often implemented to simply translate the assembly code to binary machine code via one-to-one correspondence.
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