How to get the native assembly code (e.g. x86-64 asm) for OCaml code generated by the native ocamlopt compiler?
To get the assembly code for an OCaml program, add these parameters to ocamlopt:
-S -inline 20 -nodynlink
An example is as follows.
The OCaml program:
$ cat not.ml
let not x =
((x - 1) lxor (x land (x - 1))) lsr 62
;;
not 0;;
not 1;;
not (-1);;
not (1 lsl 62);;
Compile the code:
$ ocamlopt -S -inline 20 -nodynlink not.ml -o not.opt
The assembly code generated:
$ cat not.s
.data
.globl camlNot__data_begin
camlNot__data_begin:
.text
.globl camlNot__code_begin
camlNot__code_begin:
.data
.quad 1024
.globl camlNot
camlNot:
.space 8
.data
.quad 2295
camlNot__1:
.quad camlNot__not_1008
.quad 3
.text
.align 16
.globl camlNot__not_1008
camlNot__not_1008:
.cfi_startproc
.L100:
movq %rax, %rdi
addq $-2, %rdi
movq %rax, %rbx
andq %rdi, %rbx
addq $-2, %rax
xorq %rbx, %rax
orq $1, %rax
shrq $62, %rax
orq $1, %rax
ret
.cfi_endproc
.type camlNot__not_1008,@function
.size camlNot__not_1008,.-camlNot__not_1008
.text
.align 16
.globl camlNot__entry
camlNot__entry:
.cfi_startproc
.L101:
leaq camlNot__1(%rip), %rax
movq %rax, camlNot(%rip)
movq $3, %rax
movq $1, %rax
movq $1, %rax
movq $1, %rax
movq $1, %rax
ret
.cfi_endproc
.type camlNot__entry,@function
.size camlNot__entry,.-camlNot__entry
.data
.text
.globl camlNot__code_end
camlNot__code_end:
.data
.globl camlNot__data_end
camlNot__data_end:
.long 0
.globl camlNot__frametable
camlNot__frametable:
.quad 0
.section .note.GNU-stack,"",%progbits
Here, camlNot__not_1008 is the assembly for the function not. caml is the prefix. Not is the module/file name.