Modify how llvm backend aligned

I’m trying to implement something similar to sandbox(Software fault isolation).I put the protect instruction
and danger instruction(such as call) in a basicblock and use the MachineBasicBlock::setAlignment to align it
to 32B.The results is the picture above.but i’m wondering if it’s possible to insert the no-op before the call
instruction like the picture below.
0B 32B

some protect instruction | call instruction | no-ops |
some protect instruction | no-ops | call instruction |
So is it possible to modify llvm’s X86 backend to set the layout like this?(I guess google’s native client achieve
this goal, but i can’t find any document.) I know there is no pass in MC layer, i just want to know if i modify
the source code, can i achieve this goal?
The second question, does function EmitNops in ‘llvm/lib/Target/X86/MCInstLower’ insert all no-ops to the binary?
if not, which function does?
Thanks for your help.
zheng han

You want to look for uses of the MCBoundaryAlignFragment class in the X86AsmBackend. This should provide some hints for how to insert alignment-specific fragments.