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Full Metal Jacket
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Joined: 11 Jul 2013
Posts: 14
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 Posted: Mon Oct 10, 2016 12:21 am Post subject: Call function that takes char* as param value in auto assemb |
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I have following function(its is __cdecl after compiling) and I would like to call it in auto assembler.
| Code: | void hello(const char* name)
{
cout << "Hello " << name << endl;
} |
I tried:
| Code: | fullaccess(00400500,4)
alloc(MyCode,1024)
CreateThread(MyCode)
mystr:
db 'boi',0
MyCode:
push mystr
call 004016F0
ret // exit thread |
in IDA call looks like:
| Code: | mov dword ptr [esp], offset aBoi ; "boi"
call __Z7helloPKc ; hello(char const*) |
so I tried:
| Code: | move dword ptr [esp], mystr
call 004016F0 |
but it didn't work.
Also would be nice if you could explain me why I'm giving fullaccess (to first 4 bytes?) to 400500 does it count ?
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Dark Byte
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Joined: 09 May 2003
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Location: The netherlands
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| Posted: Mon Oct 10, 2016 4:09 am Post subject: |
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You havn't described what happens so i assume the target process crashes
Since it's cdecl then you have to sub esp, 4 after the call
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Full Metal Jacket
Newbie cheater
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Joined: 11 Jul 2013
Posts: 14
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| Posted: Mon Oct 10, 2016 5:35 am Post subject: |
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| Dark Byte wrote: | You havn't described what happens so i assume the target process crashes
Since it's cdecl then you have to sub esp, 4 after the call |
Hey thank you Dark Byte it works when I added sub esp, 4. However it crashes after executing the function. What's the cause?
Before the process didn't crash, nothing happened.
EDIT:
It worked when I did add esp, 4 instead of sub dunno why but it works. Thank you very much Dark Byte you are f*** genius I wish I had knowledge you have.
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mgr.inz.Player
I post too much
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Joined: 07 Nov 2008
Posts: 4438
Location: W kraju nad Wisla. UTC+01:00
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| Posted: Mon Oct 10, 2016 2:24 pm Post subject: |
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fixed
| Quote: | | Since it's cdecl then you have to 'add esp,4' |
https://msdn.microsoft.com/en-us/library/zkwh89ks.aspx
| Code: | | Stack-maintenance responsibility: Calling function pops the arguments from the stack. |
PS: you don't need fullaccess(00400500,4)
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