[MPlayer-dev-eng] silly code

[Dylan Perry]

Hi,

AFAICT

On Tue, 1 Jan 2002, Arpi wrote:

> Hi,
> 
> another piece of shit:
> 
> 0x62924c30:     mov    %eax,%ecx
> 0x62924c32:     shr    $0x10,%ecx
> 0x62924c35:     and    $0xff,%ecx
> 0x62924c3b:     and    $0xff00ffff,%eax

I guess %eax here is really two separate index vars (stored as 0xbbaabbbb,
probably 0xaabbbb is sufficient)

> 0x62924c40:     lea    0x62b67ae0(,%ecx,8),%ecx
> 0x62924c47:     cmpb   $0x0,(%ecx)

First element in the structure determines whether the second element is
code address (0) or another table (!0) ... either jump to it or deref and
index

> 0x62924c4a:     je     0x62924c61
> 0x62924c4c:     mov    0x4(%ecx),%edx
> 0x62924c4f:     lea    0x0(,%eax,4),%ecx
> 0x62924c56:     lea    (%edx,%ecx,4),%ecx

%ecx is recalculated to the base address of the element within another
table

> 0x62924c59:     mov    (%ecx),%eax
> 0x62924c5b:     mov    0x8(%ecx),%edx
> 0x62924c5e:     jmp    *0x4(%ecx)
> 0x62924c61:     jmp    *0x4(%ecx)
> 
> it's called theQicktimeDispatcher, and seems to be something main entry
> point.
> 
> also, note the 0x62924c61 case: it sees ecx==0, so it jumps to [ecx+4]
> strict way to sig11 :)
> 
> i have to redirect this func and do somr printf on parameters.
> it doesn't work in c, i think because of parameter pasisng in eax, instead
> of stack.
> 
> currently i'm using:
> 
> static int (*real_theqt)(int a,int b,int c,int d,int e,int f,int g,int h) = NULL;
> 
> static int fake_theqt(int a,int b,int c,int d,int e,int f,int g,int h){
>     return real_theqt(a,b,c,d,e,f,g,h);
> }
> 
> and, at GetProcAddress:
>         if(!strcmp(function,"theQuickTimeDispatcher")){
>             real_theqt=retproc; retproc=fake_theqt;
> 	}
> 
> i think i need some asm for teh above, to same/restore eax?
> 
> A'rpi / Astral & ESP-team
> 
> --
> mailto:arpi at thot.banki.hu
> http://esp-team.scene.hu

It looks like it's using fastcall or something similar and will probably
pass the first two vars as %eax and %edx (those two lines before the
jmp would seem to support that).

probably need something like:
asm("push %3\n"
    "push %4\n"
    "push %5\n"
    "push %6\n"
    "push %7\n"
    "push %8\n"
    "call *%9\n"
    : "=a" (ret)
    : "0" (a), "d" (b), "g" (c), "g" (d), "g" (e), "g" (f), "g" (g),
"g" (h), "m" (func)
    : "memory", "%esi", "%edi", "%ebx", "%ecx");

from memory (if this is using fastcall) then the called func is
responsible for stack adjustment (using other form of ret that takes
an immediate operand).


Dylan Perry