OpenEuphoria

Re: ASM Help

• Posted by Mike The Spike <mtsreborn at yahoo.com> Mar 21, 2001
• 428 views

NP ma man...
Here's how to fix this...

Push the paremeters on the stack,
and then do call(address_in_mem_of_function).
Then pop the parameters.

Easy huh?
Just use Eu's call()...

Mike The Spike
--- Matthew Lewis <matthewwalkerlewis at YAHOO.COM>
wrote:
>
> I'm hoping someone here can help me out with some
> ASM.  I'm trying to push
> some parameters on the stack, first of all, and then
> call a function to
> which I have a pointer.  I've managed to move the
> params from memory to the
> stack, but I can't figure out how to call the other
> function.
>
> I've been using asm.e from Pete Eberlein, and he
> only has support for call
> near, which I don't think I can use here.  So I've
> been poking around, and
> figured out how to put together opcodes for call
> far.
>
> Has anyone done anything like this?  I've looked at
> a lot of stuff all over
> the web about ASM, and most of it really doesn't
> help, since it's usually
> geared toward MASM or the like, which is at a
> somewhat higher level than I'm
> working.  Pete's docs doesn't seem to shed any light
> on this, either,
> although I found the encoding schemes for mnemonics
> at
> http://www.imada.ou.dk/~jews/PInfo/intel.html
>
>
> Here's my code (it's been modified somewhat at 1A
> from the original output).
> The function I want to call is located at comfunc
> (which I poke in after
> putting the routine into memory).  I suspect part of
> my problem may be not
> pushing something (like the return address), but
> I've gotten the impression
> that call should do this automatically.
>
> com_asm = {
>     #60,                    --    0: pusha
>     #BB,#00,#00,#00,#00,    --    1: mov ebx,
> paramcount (2)
>     #8B,#0D,#00,#00,#00,#00,--    6: mov ecx,
> [params] (8)
>     #8B,#01,                --    C: start: mov eax,
> [ecx]
>     #50,                    --    E: push eax
>     #83,#C1,#04,            --    F: add ecx, 4
>     #4B,                    --   12: dec ebx
>     #75,#F7,                --   13: jnz start
>     #B8,#00,#00,#00,#00,    --   15: mov edx,
> comfunc (22)

>     #FF,#D8,                --   1A: call far eax
>     #58,                    --   1C: pop eax
>     #A3,#00,#00,#00,#00,    --   1D: mov
> [retpointer], eax (30)
>     #58,
>     #58,
>     #58,
>     #61,                    --   22: popa
>     #C3},                   --   23: ret
>
> When I call the routine, I get a fault.  Here's a
> dissasembly (the entry
> point is 00595610):
>
> ---------- Code Disassembly ----------
> function: <nosymbols>+0000
>         0059560f 0060bb           add
> [eax-0x45],ah
> ds:00f30b76=??
>         00595612 0300             add     eax,[eax]
> ds:00591f78=b7b85bc3
>         00595614 0000             add     [eax],al
> ds:00591f78=c3
>         00595616 8b0d087e5900     mov
> ecx,[00597e08]
> ds:00597e08=00597df8
>         0059561c 8b01             mov     eax,[ecx]
> ds:00597e04=00000011
>         0059561e 50               push    eax
>         0059561f 83c104           add     ecx,0x4
>         00595622 4b               dec     ebx
>         00595623 75f7             jnz     0059561c
>         00595625 b8781f5900       mov
> eax,0x591f78
> FAULT ->0059562a ffd8             call    eax
>         0059562c 58               pop     eax
>         0059562d a300505659       mov
> [59565000],eax
> ds:59565000=????????
>         00595632 005858           add
> [eax+0x58],bl
> ds:00f30b76=??
>         00595635 61               popad
>         00595636 c3               ret
>         00595637 0920             or      [eax],esp
> ds:00591f78=b7b85bc3
>         00595639 2020             and     [eax],ah
> ds:00591f78=c3
>         0059563b 2011             and     [ecx],dl
> ds:00597e04=11
>         0059563d 0000             add     [eax],al
> ds:00591f78=c3
>         0059563f 0020             add     [eax],ah
> ds:00591f78=c3
>         00595641 005900           add     [ecx],bl
> ds:00f36a02=??
>
> Registers:
> EAX: 00591F78 EBX: 00000000 ECX: 00597E04 EDX:
> 00000000 ESI: 00595610 EDI:
> 00000001
> EIP: 0059562A ESP: 0056FC0C EBP: 0056FC46 IOPL: 0
>      nv up ei pl zr na
> po nc
> CS: 015F  SS: 0167  DS: 0167  ES: 0167  FS: 59CF
> GS: 0000             EFL:
> 00010246
>
> Stack:
> ---------- Top of the Stack ----------
> 0056FC0C  00580030 00594E78 005F4250 00000001
> |0.X.xNY.PB_.....|
> 0056FC1C  00595610 0056FC46 0056FC38 00000028
> |.VY.F.V.8.V.(...|
> 0056FC2C  00000000 005A2644 005A2644 0041454C
> |....D&Z.D&Z.LEA.|
> 0056FC3C  005E0880 00000001 00423618 0056FC64
> |..^......6B.d.V.|
>
> ---------- Stack Back Trace ----------
> Stopped at 0059562A (0001:0059462A in (UNKNOWN))
> Base=0x00000000
> RVA=0x00001000
>
> Matt Lewis
>