On 2017/2/7 0:26, Hannes Domani wrote:
> Hello
>
>
> Does delay-loading work with 32bit executables?
>
> In the following example it crashes for me on the dll_function() call.
> I've used i686-6.3.0-release-win32-dwarf-rt_v5-rev1.7z for my tests.
I compiled the program and it did crash. The assembly code generated
looks like this:
00401570 | push ebp | int main(){
00401571 | mov ebp, esp |
00401573 | and esp, FFFFFFF0 |
00401576 | call app.401700 | __main();
0040157B | mov eax, dword ptr ds:[407204] |
00401580 | call eax |
00401582 | mov eax, 0 | return 0;
00401587 | leave |
00401588 | ret | }
0040158C | push ecx |
0040158D | push edx |
0040158E | push eax |
0040158F | push <app.sub_402DB0> |
00401594 | call app.4026A0 |
00401599 | pop edx |
0040159A | pop ecx |
0040159B | jmp eax |
The pointer at address 407204 should be a pointer to the DLL loader
function initially, which is located at 0040158C. The pointer here is
initially null and results in jumping to address zero, hence the crash.
In addition to that, the assembly code of the DLL loader function is
incorrect. The DLL loader function requires the caller to pass the
address of the function pointer above (which is 407204) via the EAX
register. That is, the first instruction at 0040158C should have been
`lea eax, dword ptr ds:[407204]`.
Compiling app.c with `-S -masm=intel` produces the following assembly
code, with directives removed:
_main:
push ebp
mov ebp, esp
and esp, -16
call ___main
mov eax, DWORD PTR __imp__dll_function
call eax
mov eax, 0
leave
ret
The DLL loader function `__imp__dll_function` seems not generated by the
compiler. So it seems that dlltool for i686 isn't generating correct
machine code for delay-loaded functions.
--
Best regards,
LH_Mouse
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