ClearLocalVariables timings

[jj2007]

The "ZerorSubVars" proc trashes only "edi" which is saved into "edx" temporally.

I'm trying to test your version:
   push offset MyProc
   call ZeroSubVars
But mov eax, [esp+4] yields 401005, which happens to be
00401005   . /E9 53000000   jmp MyProc

It works for MyProc proc private uses ... args but not for public (the default).

Will keep trying ;-)

[Ficko]

I am not sure what you are doing jj. :icon_eek:
If you call a proc with a parameter then [esp+4] is the parameter you pushed.
Therefore you push the offset of a PROC than you get the offset of a PROC.

[Ficko]

Ok, I have a thought.

If you did this:

Code Select Expand


ZeroSubVars proc public pProc:DWORD
....


It will not work.
It has to be a frameless proc.

Code Select Expand


ZeroSubVars:mov eax, [esp+4]


[jj2007]

I am not sure what you are doing jj. :icon_eek:
If you call a proc with a parameter then [esp+4] is the parameter you pushed.
Therefore you push the offset of a PROC than you get the offset of a PROC.

That sounds entirely plausible. Nonetheless, the bloody beast pushes the jump table, not the actual proc start - unless I declare it private. And of course, ZeroSubVars has option prologue:none etc.
::)

Now the good news is that I found the culprit. Testbed attached - try with and without /debug in the linker's commandline, and prepare for a fat surprise :icon_mrgreen:

P.S.: Don't use polink, use the old Masm32 default linker.

[Ficko]

Here is my test code (Tested with JWASM and ML the "bloody beast" must be "GoASM":P):

Code Select Expand


.686p
.model flat,stdcall
option casemap :none ; case sensitive
include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
includelib \masm32\lib\kernel32.lib
; *********************************************************
; turn stackframe off and on for low overhead procedures
; *********************************************************
Stackframe MACRO arg
  IFIDNI <on>,<arg>
    OPTION PROLOGUE:PrologueDef
    OPTION EPILOGUE:EpilogueDef
  ELSEIFIDNI <off>,<arg>
    OPTION PROLOGUE:NONE
    OPTION EPILOGUE:NONE
  ELSE
    echo -----------------------------------
    echo ERROR IN "stackframe" MACRO
    echo Incorrect Argument Supplied
    echo Options
    echo 1. off Turn default stack frame off
    echo 2. on  Restore stack frame defaults
    echo SYNTAX : frame on/off
    echo -----------------------------------
    .err
  ENDIF
ENDM     
; ---------------------------------------------------------
Pilot PROTO
.data
    CommandLine   dd 0
    hInstance     dd 0
.code
start:
    invoke GetModuleHandle, NULL ; provides the instance handle
    mov hInstance, eax
    invoke GetCommandLine        ; provides the command line address
    mov CommandLine, eax
     invoke Pilot
    invoke ExitProcess,eax

Stackframe off
ZeroSubVars proc public
mov eax, [esp+4]
mov ecx, dword ptr [eax+5]
.if (byte ptr [eax+4] == 0C4h)
neg ecx
.endif
.if (byte ptr [eax+3] == 83h)
movzx ecx, cl
.endif
mov edx, edi
mov edi, ecx
sub edi, ebp
neg edi
shr ecx, 2
xor eax, eax
rep stosd
mov edi, edx
ret 4
ZeroSubVars endp

Stackframe on
Pilot proc public
LOCAL MyVar :QWORD
push offset Pilot
call ZeroSubVars
ret 4
Pilot endp
end start


[jj2007]

Hi Ficko,
It's the linker. Depending on version and debug settings, it sometimes pushes the real offset, sometimes the offset of the jump table. The snippet below shows this:
00401005        offset MyPublic
00402000        offset MyPrivate
Same with polink:
00401FEE        offset MyPublic
00401FF0        offset MyPrivate

include \masm32\include\masm32rt.inc

.code
start:
   push offset MyPublic
   pop ecx
   print hex$(ecx), 9, "offset MyPublic", 13, 10

   push offset MyPrivate
   pop ecx
   inkey hex$(ecx), 9, "offset MyPrivate", 13, 10

   exit

nops 1000h-72h   ; to make it clearer

MyPublic proc public
  nop
  ret
MyPublic endp

MyPrivate proc private
  nop
  ret
MyPrivate endp

end start

OPT_Linker   link   ; polink works, 6.14 sometimes, 10.0 chokes if /debug is set
OPT_DebugA   /Zi
OPT_DebugL   /debug /DYNAMICBASE:NO
OPT_Assembler   mlv10

[Ficko]

That's really strange having no explanation. :icon_eek:

[Antariy]

Hi Jochen :t

When you're using /debug switch with the linker, and do not want to have those "jumps-to" wrappers, add /INCREMENTAL:NO switch to the linker. (Those jumps are things having two targets: fast linking scheme (incremental build), and/or are helpers in a debugging (that was especially important for breakpoints on an APIs on Win9x systems)).

[jj2007]

Thanks, Alex, that solves the mystery :t

We had a long thread about the IAT jump tables in the old forum. For my "zero locals" macro, the problem is not relevant because I chose to go back and look for mov ebp, esp, but Ficko's version relies on direct calls, so the linker behaviour needs to be watched.

[Antariy]

Yes, IAT jump thunks are not absolutely equal to "incremental/debug-mode" ones, but very similar things.

Interesting, with search of /INCREMENTAL found this thread on the old forum, too:
http://www.masmforum.com/board/index.php?topic=795.msg5491#msg5491

[jj2007]

Thanks to everybody :icon14:

The fastest algo is now part of the MasmBasic library (more).