Calling a C function from ASM in user-mode driver

OSR_Community_User · February 21, 2011, 1:41pm

I have a user-mode driver (DLL) that I’m compiling with the WDK. The driver
uses an ASM file that’s included in the build process like so:

I386_SOURCES= \
i386\stub.asm

The ASM file is calls a C-function, but for some reason the linker ends up
with an unresolved symbol error.

The C-function I’m trying to call is defined as follows:

extern “C” void GetPtrGetKtProcAddress()
{
}

The ASM file looks as follows:

.586
.MODEL FLAT, C

EXTRN GetPtrGetKtProcAddress:proc

.DATA

.CODE

; Function prototypes
public GetKtProcAddress

GetKtProcAddress proc
pushad
call GetPtrGetKtProcAddress
ret

GetKtProcAddress endp

_text ends
end

The code compiles and links fine in VS2010, so I’m thinking I’m missing
something specific to the WDK somewhere.

Don_Burn_1 · February 21, 2011, 1:49pm

The WDK specifies different calling conventions than Visual C’s
defaults. You need to explicitly define the calling convention for the
C routine.

Don Burn (MVP, Windows DKD)
Windows Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr

“Soren Dreijer” wrote in message
news:xxxxx@ntdev:

> I have a user-mode driver (DLL) that I’m compiling with the WDK. The driver
> uses an ASM file that’s included in the build process like so:
>
> I386_SOURCES= > i386\stub.asm
>
> The ASM file is calls a C-function, but for some reason the linker ends up
> with an unresolved symbol error.
>
> The C-function I’m trying to call is defined as follows:
>
> extern “C” void GetPtrGetKtProcAddress()
> {
> }
>
> The ASM file looks as follows:
>
> .586
> .MODEL FLAT, C
>
> EXTRN GetPtrGetKtProcAddress:proc
>
> .DATA
>
> .CODE
>
> ; Function prototypes
> public GetKtProcAddress
>
> GetKtProcAddress proc
> pushad
> call GetPtrGetKtProcAddress
> ret
>
> GetKtProcAddress endp
>
> _text ends
> end
>
> The code compiles and links fine in VS2010, so I’m thinking I’m missing
> something specific to the WDK somewhere.

OSR_Community_User · February 21, 2011, 1:53pm

Well, there we go. That was easy.

I had already explicitly tried __stdcall but that obviously didn’t work
since the prototype I had in the ASM file was for a __cdecl function.

Cheers!

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:bounce-441913-
xxxxx@lists.osr.com] On Behalf Of Don Burn
Sent: Monday, February 21, 2011 12:49 PM
To: Windows System Software Devs Interest List
Subject: Re:[ntdev] Calling a C function from ASM in user-mode driver

The WDK specifies different calling conventions than Visual C’s defaults.
You
need to explicitly define the calling convention for the C routine.

Don Burn (MVP, Windows DKD)
Windows Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr

“Soren Dreijer” wrote in message
> news:xxxxx@ntdev:
>
> > I have a user-mode driver (DLL) that I’m compiling with the WDK. The
> > driver uses an ASM file that’s included in the build process like so:
> >
> > I386_SOURCES= > > i386\stub.asm
> >
> > The ASM file is calls a C-function, but for some reason the linker
> > ends up with an unresolved symbol error.
> >
> > The C-function I’m trying to call is defined as follows:
> >
> > extern “C” void GetPtrGetKtProcAddress() { }
> >
> > The ASM file looks as follows:
> >
> > .586
> > .MODEL FLAT, C
> >
> > EXTRN GetPtrGetKtProcAddress:proc
> >
> > .DATA
> >
> > .CODE
> >
> > ; Function prototypes
> > public GetKtProcAddress
> >
> > GetKtProcAddress proc
> > pushad
> > call GetPtrGetKtProcAddress
> > ret
> >
> > GetKtProcAddress endp
> >
> > _text ends
> > end
> >
> > The code compiles and links fine in VS2010, so I’m thinking I’m
> > missing something specific to the WDK somewhere.
>
>
> —
> NTDEV is sponsored by OSR
>
> For our schedule of WDF, WDM, debugging and other seminars visit:
> http://www.osr.com/seminars
>
> To unsubscribe, visit the List Server section of OSR Online at
> http://www.osronline.com/page.cfm?name=ListServer

Maxim_S_Shatskih · February 21, 2011, 2:11pm

__cdecl: _FuncName
__stdcall: xxxxx@DecimalParamSizeInBytes

–
Maxim S. Shatskih
Windows DDK MVP
xxxxx@storagecraft.com
http://www.storagecraft.com

“Soren Dreijer” wrote in message news:xxxxx@ntdev…
> Well, there we go. That was easy.
>
> I had already explicitly tried stdcall but that obviously didn’t work
> since the prototype I had in the ASM file was for a cdecl function.
>
> Cheers!
>
>> -----Original Message-----
>> From: xxxxx@lists.osr.com [mailto:bounce-441913-
>> xxxxx@lists.osr.com] On Behalf Of Don Burn
>> Sent: Monday, February 21, 2011 12:49 PM
>> To: Windows System Software Devs Interest List
>> Subject: Re:[ntdev] Calling a C function from ASM in user-mode driver
>>
>> The WDK specifies different calling conventions than Visual C’s defaults.
> You
>> need to explicitly define the calling convention for the C routine.
>>
>>
>> Don Burn (MVP, Windows DKD)
>> Windows Filesystem and Driver Consulting
>> Website: http://www.windrvr.com
>> Blog: http://msmvps.com/blogs/WinDrvr
>>
>>
>>
>>
>> “Soren Dreijer” wrote in message
>> news:xxxxx@ntdev:
>>
>> > I have a user-mode driver (DLL) that I’m compiling with the WDK. The
>> > driver uses an ASM file that’s included in the build process like so:
>> >
>> > I386_SOURCES= >> > i386\stub.asm
>> >
>> > The ASM file is calls a C-function, but for some reason the linker
>> > ends up with an unresolved symbol error.
>> >
>> > The C-function I’m trying to call is defined as follows:
>> >
>> > extern “C” void GetPtrGetKtProcAddress() { }
>> >
>> > The ASM file looks as follows:
>> >
>> > .586
>> > .MODEL FLAT, C
>> >
>> > EXTRN GetPtrGetKtProcAddress:proc
>> >
>> > .DATA
>> >
>> > .CODE
>> >
>> > ; Function prototypes
>> > public GetKtProcAddress
>> >
>> > GetKtProcAddress proc
>> > pushad
>> > call GetPtrGetKtProcAddress
>> > ret
>> >
>> > GetKtProcAddress endp
>> >
>> > _text ends
>> > end
>> >
>> > The code compiles and links fine in VS2010, so I’m thinking I’m
>> > missing something specific to the WDK somewhere.
>>
>>
>> —
>> NTDEV is sponsored by OSR
>>
>> For our schedule of WDF, WDM, debugging and other seminars visit:
>> http://www.osr.com/seminars
>>
>> To unsubscribe, visit the List Server section of OSR Online at
>> http://www.osronline.com/page.cfm?name=ListServer
>
>

Gene_Soudlenkov · February 21, 2011, 3:39pm

Just add _ before the asm name:

_GetKtProcAddress proc

Also, make sure you handle stack correctly

Gene

On 22/02/11 07:53, Soren Dreijer wrote:

Well, there we go. That was easy.

I had already explicitly tried __stdcall but that obviously didn’t work
since the prototype I had in the ASM file was for a __cdecl function.

Cheers!

> -----Original Message-----
> From: xxxxx@lists.osr.com [mailto:bounce-441913-
> xxxxx@lists.osr.com] On Behalf Of Don Burn
> Sent: Monday, February 21, 2011 12:49 PM
> To: Windows System Software Devs Interest List
> Subject: Re:[ntdev] Calling a C function from ASM in user-mode driver
>
> The WDK specifies different calling conventions than Visual C’s defaults.
You
> need to explicitly define the calling convention for the C routine.
>
>
> Don Burn (MVP, Windows DKD)
> Windows Filesystem and Driver Consulting
> Website: http://www.windrvr.com
> Blog: http://msmvps.com/blogs/WinDrvr
>
>
>
>
> “Soren Dreijer” wrote in message
>> news:xxxxx@ntdev:
>>
>>> I have a user-mode driver (DLL) that I’m compiling with the WDK. The
>>> driver uses an ASM file that’s included in the build process like so:
>>>
>>> I386_SOURCES= >>> i386\stub.asm
>>>
>>> The ASM file is calls a C-function, but for some reason the linker
>>> ends up with an unresolved symbol error.
>>>
>>> The C-function I’m trying to call is defined as follows:
>>>
>>> extern “C” void GetPtrGetKtProcAddress() { }
>>>
>>> The ASM file looks as follows:
>>>
>>> .586
>>> .MODEL FLAT, C
>>>
>>> EXTRN GetPtrGetKtProcAddress:proc
>>>
>>> .DATA
>>>
>>> .CODE
>>>
>>> ; Function prototypes
>>> public GetKtProcAddress
>>>
>>> GetKtProcAddress proc
>>> pushad
>>> call GetPtrGetKtProcAddress
>>> ret
>>>
>>> GetKtProcAddress endp
>>>
>>> _text ends
>>> end
>>>
>>> The code compiles and links fine in VS2010, so I’m thinking I’m
>>> missing something specific to the WDK somewhere.
>>
>> —
>> NTDEV is sponsored by OSR
>>
>> For our schedule of WDF, WDM, debugging and other seminars visit:
>> http://www.osr.com/seminars
>>
>> To unsubscribe, visit the List Server section of OSR Online at
>> http://www.osronline.com/page.cfm?name=ListServer
>
> —
> NTDEV is sponsored by OSR
>
> For our schedule of WDF, WDM, debugging and other seminars visit:
> http://www.osr.com/seminars
>
> To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer

OSR_Community_User · February 21, 2011, 4:42pm

That was not the issue though. The issue was that the wrong default calling
convention was used by the compiler for my C function such that it got
mangled (as Maxim showed).

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:bounce-441934-
xxxxx@lists.osr.com] On Behalf Of Gene Soudlenkov
Sent: Monday, February 21, 2011 2:33 PM
To: Windows System Software Devs Interest List
Subject: Re: [ntdev] Calling a C function from ASM in user-mode driver

Just add _ before the asm name:

_GetKtProcAddress proc

Also, make sure you handle stack correctly

Gene

On 22/02/11 07:53, Soren Dreijer wrote:
> Well, there we go. That was easy.
>
> I had already explicitly tried __stdcall but that obviously didn’t
> work since the prototype I had in the ASM file was for a __cdecl
function.
>
> Cheers!
>
>> -----Original Message-----
>> From: xxxxx@lists.osr.com [mailto:bounce-441913-
>> xxxxx@lists.osr.com] On Behalf Of Don Burn
>> Sent: Monday, February 21, 2011 12:49 PM
>> To: Windows System Software Devs Interest List
>> Subject: Re:[ntdev] Calling a C function from ASM in user-mode driver
>>
>> The WDK specifies different calling conventions than Visual C’s
defaults.
> You
>> need to explicitly define the calling convention for the C routine.
>>
>>
>> Don Burn (MVP, Windows DKD)
>> Windows Filesystem and Driver Consulting
>> Website: http://www.windrvr.com
>> Blog: http://msmvps.com/blogs/WinDrvr
>>
>>
>>
>>
>> “Soren Dreijer” wrote in message
> >> news:xxxxx@ntdev:
> >>
> >>> I have a user-mode driver (DLL) that I’m compiling with the WDK. The
> >>> driver uses an ASM file that’s included in the build process like so:
> >>>
> >>> I386_SOURCES= > >>> i386\stub.asm
> >>>
> >>> The ASM file is calls a C-function, but for some reason the linker
> >>> ends up with an unresolved symbol error.
> >>>
> >>> The C-function I’m trying to call is defined as follows:
> >>>
> >>> extern “C” void GetPtrGetKtProcAddress() { }
> >>>
> >>> The ASM file looks as follows:
> >>>
> >>> .586
> >>> .MODEL FLAT, C
> >>>
> >>> EXTRN GetPtrGetKtProcAddress:proc
> >>>
> >>> .DATA
> >>>
> >>> .CODE
> >>>
> >>> ; Function prototypes
> >>> public GetKtProcAddress
> >>>
> >>> GetKtProcAddress proc
> >>> pushad
> >>> call GetPtrGetKtProcAddress
> >>> ret
> >>>
> >>> GetKtProcAddress endp
> >>>
> >>> _text ends
> >>> end
> >>>
> >>> The code compiles and links fine in VS2010, so I’m thinking I’m
> >>> missing something specific to the WDK somewhere.
> >>
> >> —
> >> NTDEV is sponsored by OSR
> >>
> >> For our schedule of WDF, WDM, debugging and other seminars visit:
> >> http://www.osr.com/seminars
> >>
> >> To unsubscribe, visit the List Server section of OSR Online at
> >> http://www.osronline.com/page.cfm?name=ListServer
> >
> > —
> > NTDEV is sponsored by OSR
> >
> > For our schedule of WDF, WDM, debugging and other seminars visit:
> > http://www.osr.com/seminars
> >
> > To unsubscribe, visit the List Server section of OSR Online at
> > http://www.osronline.com/page.cfm?name=ListServer
>
>
> —
> NTDEV is sponsored by OSR
>
> For our schedule of WDF, WDM, debugging and other seminars visit:
> http://www.osr.com/seminars
>
> To unsubscribe, visit the List Server section of OSR Online at
> http://www.osronline.com/page.cfm?name=ListServer

OSR_Community_User · February 23, 2011, 1:15am

extern “C” means you are compiling in C++.

You did not specify the calling convention.

extern “C” void __cdecl GetPtrGetKtProcAddress();

the name is therefore

_GetPtrGetKtProcAddress

and if in a DLL might be

__imp__GetPtrGetKtProcAddress

when in doubt, use some useful utility to examine the file you are linking
to, like the dumpbin utility
joe

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Soren Dreijer
Sent: Monday, February 21, 2011 1:41 PM
To: Windows System Software Devs Interest List
Subject: [ntdev] Calling a C function from ASM in user-mode driver