There is no real reason why you should. Remember that EAX is only a 32-bit register, while all the FPU registers are 80 bits in width, because the FPU does calculations on 80-bit floats by default. Therefore, moving data from the FPU register to a general purpose register will cause data loss. If you really want to … Read more
As others have pointed out, LEA (load effective address) is often used as a “trick” to do certain computations, but that’s not its primary purpose. The x86 instruction set was designed to support high-level languages like Pascal and C, where arrays—especially arrays of ints or small structs—are common. Consider, for example, a struct representing (x, … Read more
AT&T syntax splits the movzx Intel instruction mnemonic into different mnemonics for different source sizes (movzb vs. movzw). In Intel syntax, it’s: i.e. load a byte from memory at eax+ecx+1 and zero-extend to full register. BTW, most GNU tools now have a switch or a config option to prefer Intel syntax. (Such as objdump -Mintel or gcc -S -masm=intel, although the latter affects … Read more
lw (load word) loads a word from memory to a register. $2 is the destination register and $4 the address register. And the source of information is the memory. 4 is an offset that is added (not multiplied) to the address register. This kind of memory access is called based addressing and is it quite … Read more
Machine code is binary (1’s and 0’s) code that can be executed directly by the CPU. If you open a machine code file in a text editor you would see garbage, including unprintable characters (no, not those unprintable characters 😉 ). Object code is a portion of machine code not yet linked into a complete program. It’s the machine … Read more
its pretty much just shifting all the bits left by 1 The example they showed was a shift by 1 bit. The sll instruction isn’t limited to just shifting by 1 bit; you can specify a shift amount in the range 0..31 (a shift by 0 might seem useless, but SLL $zero, $zero, 0 is used to encode a NOP on … Read more
means: move a literal decimal-10 long (4-bytes) into a 4-byte memory location that begins at the address pointed to by (the esp register plus decimal 24)–basically it is a local variable.
cmp arg2, arg1 performs the same operation as sub arg2, arg1 except that none of the operands are modified. The difference is not stored anywhere. However, the flags register is updated and can be used in a conditional jump, like jump-if-equal (JE), most often as the next instruction after the cmp. The advantage over other … Read more
As others have pointed out, LEA (load effective address) is often used as a “trick” to do certain computations, but that’s not its primary purpose. The x86 instruction set was designed to support high-level languages like Pascal and C, where arrays—especially arrays of ints or small structs—are common. Consider, for example, a struct representing (x, … Read more