I'm trying to get a feel for the assembly output by GHC on my platform. Below is a module containing one function and the associated assembly. I've put in comments what I think is going on, but I'd appreciate it if anyone could give me some pointers. I'd really like to know three things: * Why does _Add_unsafeShiftR_info check if (%esi) is 3? * What's going on in _s86_info? * At the end of _s87_info, 8 is added to %ebp and then jumped to. Is that a jump to the I# constructor and, if so, how did it's address get to that offset from %ebp? Thanks in advance for any assistance! Justin --- cut here ---- # Compiled with # # ghc -c Add.hs -fext-core -keep-s-files -fasm -O2 -ddump-to-file -ddump-stg -ddump-cmm # # Platform: Windows XP. # Processor Pentium 4. # GHC Version: 6.8.2. # # > {-# OPTIONS_GHC -fglasgow-exts -fbang-patterns #-} # > module Add (unsafeShiftR) # # > where # # > import Data.Bits # > import GHC.Base (uncheckedShiftRL#, Int(..), word2Int#, int2Word#) # # > I# a `unsafeShiftR` I# b = I# (word2Int# (int2Word# a `uncheckedShiftRL#` b)) # .data .align 4 .globl _Add_unsafeShiftR_closure _Add_unsafeShiftR_closure: .long _Add_unsafeShiftR_info # Specifies entry point for unsafeShiftR? .text .align 4,0x90 .long 33 .long 34 _s87_info: addl $8,%edi cmpl 92(%ebx),%edi # Stack check? ja .Lc8n movl 4(%ebp),%eax # Get value to be shifted movl 3(%esi),%ecx # Get shift amount shrl %cl,%eax # Shift value movl $_base_GHCziBase_Izh_con_info,-4(%edi) # Get ready to call I#? movl %eax,(%edi) # Constructor value leal -3(%edi),%esi # Address to what in I#? addl $8,%ebp # Make room on stack for next caller? jmp *(%ebp) # Go to constructor? Tail call? .Lc8n: movl $8,112(%ebx) jmp *-8(%ebx) # Error routine if stack overflows? .text .align 4,0x90 .long 1 .long 34 _s86_info: movl 4(%ebp),%eax # Testing what here? movl 3(%esi),%ecx movl %ecx,4(%ebp) movl %eax,%esi movl $_s87_info,(%ebp) testl $3,%esi jne _s87_info jmp *(%esi) .text .align 4,0x90 .long 131084 .long 0 .long 15 .globl _Add_unsafeShiftR_info _Add_unsafeShiftR_info: movl (%ebp),%esi movl $_s86_info,(%ebp) testl $3,%esi # Looking at StgRetInfoTable here? jne _s86_info # Enter body of unsafeShiftR? jmp *(%esi) .data .align 4 __module_registered: .long 0 .text .align 4,0x90 .globl ___stginit_Add_ ___stginit_Add_: cmpl $0,__module_registered jne .Lc8E .Lc8F: movl $1,__module_registered addl $-4,%ebp movl $___stginit_base_GHCziBase_,(%ebp) addl $-4,%ebp movl $___stginit_base_Prelude_,(%ebp) addl $-4,%ebp movl $___stginit_base_DataziBits_,(%ebp) .Lc8E: addl $4,%ebp jmp *-4(%ebp) .text .align 4,0x90 .globl ___stginit_Add ___stginit_Add: jmp ___stginit_Add_ .ident "GHC 6.8.2"