I was trying to get disassembly of asm.js compiled by IonMonkey a couple of months ago. I had to run SpiderMonkey under gdb and disassemble the JITted entry points. (Or maybe I didn't...)
I don't know if this dumps the disassembly for asm.js. I suspect it can't, since asm.js modules are AOT compiled into a single big block of code - but maybe it'll work. Give it a try!
I was trying to get disassembly of asm.js compiled by IonMonkey a couple of months ago. I had to run SpiderMonkey under gdb and disassemble the JITted entry points. (Or maybe I didn't...)