[GHC] #8955: Syscall intrinsic

[GHC]

#8955: Syscall intrinsic
-------------------------------------+-------------------------------------
        Reporter:  schyler           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by slyfox):

 * cc: slyfox (added)


Comment:

 What is your vision on how it's supposed to be used in haskell?

 A new 'foreign import' type per OS/arch target type?

 A new syntax to be able to call assembly instructions directly from
 haskell?

 > Also, marginally increased speed for calling syscalls since it doesn't
 need to go through libffi into C-land.

 On at least i386 and amd64 GHC does not use libffi to call simple libc
 functions.
 For 'foreign import ccall unsafe' symbols GHC emits '''call <symbol>'''
 instruction directly.
 Native/via-libc difference might be in order of a few instructions.
 Note the amount of existing indirections:

 {{{#!hs
 module M where

 import Foreign.C

 foreign import ccall unsafe "foo" c_foo :: CInt -> IO CInt
 }}}
 gets translated to
 {{{
 .section .data
 .align 8
 .align 1
 .globl __stginit_M
 .type __stginit_M, @object
 __stginit_M:
 .section .rodata
 .align 8
 .align 1
 c2oj_str:
         .byte   109
         .byte   97
         .byte   105
         .byte   110
         .byte   0
 .section .data
 .align 8
 .align 1
 .globl M_zdtrModule2_closure
 .type M_zdtrModule2_closure, @object
 M_zdtrModule2_closure:
         .quad   ghczmprim_GHCziTypes_TrNameS_static_info
         .quad   c2oj_str
 .section .rodata
 .align 8
 .align 1
 c2om_str:
         .byte   77
         .byte   0
 .section .data
 .align 8
 .align 1
 .globl M_zdtrModule1_closure
 .type M_zdtrModule1_closure, @object
 M_zdtrModule1_closure:
         .quad   ghczmprim_GHCziTypes_TrNameS_static_info
         .quad   c2om_str
 .section .data
 .align 8
 .align 1
 .globl M_zdtrModule_closure
 .type M_zdtrModule_closure, @object
 M_zdtrModule_closure:
         .quad   ghczmprim_GHCziTypes_Module_static_info
         .quad   M_zdtrModule2_closure+1
         .quad   M_zdtrModule1_closure+1
         .quad   3
 .section .data
 .align 8
 .align 1
 r2eE_closure:
         .quad   r2eE_info
 .section .text
 .align 8
 .align 8
         .quad   8589934597
         .quad   0
         .quad   15
 r2eE_info:
 .Lc2ow:
         leaq -8(%rbp),%rax
         cmpq %r15,%rax
         jb .Lc2oF
 .Lc2oG:
         movq $c2ot_info,-8(%rbp)
         movq %r14,%rbx
         addq $-8,%rbp
         testb $7,%bl
         jne .Lc2ot
 .Lc2ou:
         jmp *(%rbx)
 .Lc2oJ:
         movq $16,904(%r13)
         jmp stg_gc_unpt_r1
 .align 8
         .quad   0
         .quad   31
 c2ot_info:
 .Lc2ot:
         addq $16,%r12
         cmpq 856(%r13),%r12
         ja .Lc2oJ
 .Lc2oI:
         movq 7(%rbx),%rdi
         subq $8,%rsp
         xorl %eax,%eax
         call foo
         addq $8,%rsp
         movq $base_GHCziInt_I32zh_con_info,-8(%r12)
         movslq %eax,%rax
         movq %rax,(%r12)
         leaq -7(%r12),%rbx
         addq $8,%rbp
         jmp *(%rbp)
 .Lc2oF:
         movl $r2eE_closure,%ebx
         jmp *-8(%r13)
         .size r2eE_info, .-r2eE_info
 .section .data
 .align 8
 .align 1
 .globl M_czufoo_closure
 .type M_czufoo_closure, @object
 M_czufoo_closure:
         .quad   M_czufoo_info
 .section .text
 .align 8
 .align 8
         .quad   8589934597
         .quad   0
         .quad   15
 .globl M_czufoo_info
 .type M_czufoo_info, @object
 M_czufoo_info:
 .Lc2oT:
         jmp r2eE_info
         .size M_czufoo_info, .-M_czufoo_info
 .section .data.rel.ro
 .align 8
 .align 1
 S2p0_srt:
 .section .note.GNU-stack,"", at progbits
 .ident "GHC 8.1.20160817"
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8955#comment:3>
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