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Hi its again me


In the process of implementing a "jump" log to GensKmod (not me, Kaneda), I wanted to know if there is a fixed ram area where appear the "current" function number.

I mean, each time the user jump to the bios, does the bios write the function number (d0) somewhere?

I vaguely remember the function number is written somewhere but i cannot recall where I read that.

If someone recall don't hesitate

Pfew... My english is more and more bad... I wonder what's happen.
Sorry.

all of this because Starcream allows hook on read/write memory but not program section

so I tried to mod i_jsr but Starscream is really hard to understand
I tried to add a call to my function but everything explode since x86 registers are lost with this call...

and I discovered sub68k_context.pc != sub68k_readPC( ), which I don't understand!


Stef, if you have any hint

sub68k_context.pc contains "Fetch Region pointer + PC value" then you can directly do :
mov eax, [sub68k_context.pc]
to fetch/read the current intruction. This is done for speed reason of course. If you want the real PC value, use ReadPC or unbase pc : sub68k_context.pc - sub68k_context.basePC

I'm not sur about the sub68k_context.basePC variable name since i'm doing it from head :p

basePC is for the 32X not the 68k

32X SH2 cores uses the same type of based PC.
Well, i just had a look in starscream source, here's register value at "alive" (in execution) time :
- esi = based pc
- ebp = fetch base

If you want only the pc value you have to do that :
mov eax, esi ; get based pc
sub eax, ebx ; unbase it --> eax = pc value

hope it helps you

so it means my PC value is wrong for a long time (on main 68k part)
thanks for the hint, and now understand better some stuff on Starscream (like the code below)

can you help me on this too it's the code of the jsr + my call
this code is executed the first time but freeze Gens after that..
I suspect the call to the C function SpyCDBiosCall to mod the x86 register
can you confirm this and if yes, how can i backup reg/call/restore reg?
(movem ? push ?)

KanedaFr wrote:so it means my PC value is wrong for a long time (on main 68k part)
thanks for the hint, and now understand better some stuff on Starscream (like the code below)

can you help me on this too

Code: Select all

mov ecx,esi
sub ecx,ebp
mov esi,edx
call _SpyCDBiosCall

it's the code of the jsr + my call
this code is executed the first time but freeze Gens after that..
I suspect the call to the C function SpyCDBiosCall to mod the x86 register
can you confirm this and if yes, how can i backup reg/call/restore reg?
(movem ? push ?)

Seems your _SpyCDBiosCall is using fastcall convention (ecx and edx as parameters).
I do understand you're putting PC in ecx, but what the "mov esi, edx" is supposed to do ? by doing that, you're just erasing the current pc...
Also when you do a function call, you lost your eax, ecx, edx registers values so push them if needed

the first 3 lines are the original 'jsr xxx' emulation stuff
I just add the call _Spy....

I found this
http://nasm.sourceforge.net/doc/html/na ... tion-8.1.2 but they talk about save.restore inside the callee function...
does it mean VC isn't making a clean function ?


and this http://www.delorie.com/djgpp/doc/ug/asm/calling.html
talk about

Expect the registers %eax, %ecx, and %edx, as well as the floating-point stack, to have changed. Standard library functions may modify the %gs register, and the _far* functions may modify %fs. Other registers will be preserved.