SAR command in X86 assembly with one parameter

assembly x86 disassembly
Kevin picture Kevin · Oct 10, 2012 · Viewed 21.7k times · Source

In a disassembled program I'm analyzing, I found the command

sar %eax

What does this do? I know that sar with two arguments performs a right shift, but I can't find what it means with only one parameter.

This program was compiled for an Intel x86 processor.

Answer

Necrolis picture Necrolis · Oct 10, 2012

Looks like the dissembler used short-hand for SAR EAX,1 which has an opcode of 0xD1F8. when the immediate is not 1, aka SAR EAX,xx, the opcode is 0xC1F8 xx, see the Intel Instruction reference, Vol. 2B, 4-353.

Related questions

What does "short" jump mean in assembly language?

What does the "SHORT" mean in this code? JE SHORT 00013FB8

Read More
Switch Case Assembly Language

I am looking at the assembly language code of a switch statement. I understand how the code works and what the cases are. My question is how do I decide on the case names? Below is the assembly language code, …

Read More
Need help understanding E8 asm call instruction x86

I need a helping hand in order to understand the following assembly instruction. It seems to me that I am calling a address at someUnknownValue += 20994A? E8 32F6FFFF - call std::_Init_locks::operator=+20994A

Read More