A reference for AT&T syntax assembly floating point arithmetic

 

I've been trying for the past week to find a decent resource on floating point arithmetic for x86 assembly using AT&T syntax. Ideally, a list of the opcodes, what they do, and where the floats are stored. I am familiar with IEEE 754 representation. I am not familiar with the floating point stack, and any assembly referring to floating point arithmetic.

It's strange how difficult this is to find.

EDIT: I've been looking at gcc -S output for the past month learning the assembly. That's how I figured out everything except floating point arithmetic. Even after going through dozens of small programs compiled without optimizations, I still can't figure out much about the floating point opcodes and the stack. I've only found trivial examples online.

Okay. Start with Intel syntax first, because most x86 assembly coders use it. Intel's manuals are a great resource for learning about how the x86 handles floating-point stuff.

After you learn x86 assembly in general, AT&T syntax isn't so hard to learn. The main things to note are:

  • registers are prefixed by % ; numeric constants are prefixed by $
  • register order is swapped for most two-operand instructions (ie, source first, target last)
  • instruction names specify the size; so instead of mov dword ptr [ebx], 1337 , you'd say movl $1337, (%ebx) .
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