[uml-devel] skas3 patch breaks ATI video drivers

[uml-devel] skas3 patch breaks ATI video drivers

[Marcus Better]

Hi all,

I applied Blaisorblade's host-skas3-2.6.9-v7.patch, and it breaks the 
fglrx graphics driver from ATI[1]. This is with Debian kernel 2.6.9, but 
I believe it applies to vanilla kernels also.

The problem is the following declaration added to include/asm-i386/desc.h:

----------------------------------------------------------
extern int modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
		      unsigned long bytecount);
----------------------------------------------------------

The fglrx driver contains the following macro in a source file:

_syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long, 
bytecount )

Here the compiler chokes with the following error:
---------------------------------------------------------
/usr/src/modules/fglrx-4.3.0-3.14.6/firegl_public.c:181: error: 
conflicting types for `modify_ldt'
include/asm/desc.h:144: error: previous declaration of `modify_ldt'
---------------------------------------------------------

I don't understand the details of the kernel code, but it seems that the 
problem is that the SKAS patch defines the function modify_ldt which 
conflicts with the syscall macros.

I renamed the new function to _modify_ldt instead (and changed the two 
or three references to it in ldt.c), and this seems to fix the problem.

Please CC replies to me, I'm not subscribed to the list.

Thanks for your work!

Marcus B.

[1] http://www.ati.com/support/drivers/linux/radeon-linux.html




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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Blaisorblade]

On Monday 24 January 2005 20:43, Marcus Better wrote:
> Hi all,
>
> I applied Blaisorblade's host-skas3-2.6.9-v7.patch, and it breaks the
> fglrx graphics driver from ATI[1]. This is with Debian kernel 2.6.9, but
> I believe it applies to vanilla kernels also.
>
> The problem is the following declaration added to include/asm-i386/desc.h:
>
> ----------------------------------------------------------
> extern int modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
>         unsigned long bytecount);
> ----------------------------------------------------------
>
> The fglrx driver contains the following macro in a source file:
>
> _syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long,
> bytecount )
>
> Here the compiler chokes with the following error:
> ---------------------------------------------------------
> /usr/src/modules/fglrx-4.3.0-3.14.6/firegl_public.c:181: error:
> conflicting types for `modify_ldt'
> include/asm/desc.h:144: error: previous declaration of `modify_ldt'
> ---------------------------------------------------------
>
> I don't understand the details of the kernel code, but it seems that the
> problem is that the SKAS patch defines the function modify_ldt which
> conflicts with the syscall macros.

> I renamed the new function to _modify_ldt instead (and changed the two
> or three references to it in ldt.c), and this seems to fix the problem.

I.e. the compilation problem is not in the kernel module, right? In this case, 
the problem is that you have /usr/include/asm symlinked to your kernel's 
include/asm-i386 directory, which is the wrong setup. However your solution 
should not give any problem.

If this is wrong, instead, then you are surely right... but then the solution 
you explain would be unlikely to fix anything... and the code would also be 
different, I guess. It's just a quick shoot however, so feel free to correct 
me.
> Please CC replies to me, I'm not subscribed to the list.

> Thanks for your work!
Thanks to you for using UML!
> Marcus B.
>
> [1] http://www.ati.com/support/drivers/linux/radeon-linux.html

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Marcus Better]

Blaisorblade wrote:

> I.e. the compilation problem is not in the kernel module, right?

Yes, the compilation error is in compiling the fglrx module.

> In this case, the problem is that you have /usr/include/asm symlinked to your kernel's 
> include/asm-i386 directory,

No, I don't, but I use Debian's make-kpkg which probably uses header 
files from the kernel tree. This is the normal method of building 
kernels on Debian, though.

I might add that I tried to fix the problem directly in the fglrx 
module, but it doesn't seem to work. It really must use the name 
modify_ldt in the macro, and this conflicts with the UML patch.

Marcus


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Blaisorblade]

On Tuesday 25 January 2005 09:35, Marcus Better wrote:
> Blaisorblade wrote:
> > I.e. the compilation problem is not in the kernel module, right?
>
> Yes, the compilation error is in compiling the fglrx module.
Ok, unexpected.
> > In this case, the problem is that you have /usr/include/asm symlinked to
> > your kernel's include/asm-i386 directory,
>
> No, I don't, but I use Debian's make-kpkg which probably uses header
> files from the kernel tree. This is the normal method of building
> kernels on Debian, though.
Well, since it is a kernel module, then it's correct...
> I might add that I tried to fix the problem directly in the fglrx
> module, but it doesn't seem to work.

> It really must use the name 
> modify_ldt in the macro
Yes, because the name in the macro is used to build the "__NR_modify_ldt"
> , and this conflicts with the UML patch.

Ok, this makes me wonder a bit... there is something which may cause conflicts 
in the UML patch (i.e. renaming modify_ldt that way), but it is very 
*strange* that a kernel module uses the "_syscall" macro to do a syscall with 
"int 0x80" while already being in kernelspace...

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Marcus Better]

Blaisorblade wrote:
> *strange* that a kernel module uses the "_syscall" macro to do a syscall with 
> "int 0x80" while already being in kernelspace...

It's interesting that the module contains the following code:

------------------------
//#define FGL_USE_SCT /* for developer use only */

//...<snip>...


#ifdef FGL_USE_SCT
// get direct function pointers from sys_call_table for calling
#else /* FGL_USE_SCT */
// call functions indirectly by using the syscall macros,
// entrypoints get defined by below constructs

#if !defined(__ia64__)
// the macros do use errno variable
static int errno;
#endif // __ia64__

// int mlock(const void *addr, size_t len);
_syscall2(int, mlock, const void *, addr, size_t, len )
// int munlock(const void *addr, size_t len);
_syscall2(int, munlock, const void *, addr, size_t, len )
#if !defined(__ia64__)
#if !defined(__x86_64__)
// TODO: ia64
// int modify_ldt(int func, void *ptr, unsigned long bytecount);
_syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long, 
bytecount )
#endif
#endif
#endif /* FGL_USE_SCT */
--------------------------

I actually tried to #define FGL_USE_SCT, but it didn't compile either.


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Blaisorblade]

On Tuesday 25 January 2005 11:55, Marcus Better wrote:
> Blaisorblade wrote:
> > *strange* that a kernel module uses the "_syscall" macro to do a syscall
> > with "int 0x80" while already being in kernelspace...
>
> It's interesting that the module contains the following code:
>
> ------------------------
> //#define FGL_USE_SCT /* for developer use only */
>
> //...<snip>...
>
>
> #ifdef FGL_USE_SCT
> // get direct function pointers from sys_call_table for calling
> #else /* FGL_USE_SCT */
> // call functions indirectly by using the syscall macros,
> // entrypoints get defined by below constructs
>
> #if !defined(__ia64__)
> // the macros do use errno variable
> static int errno;
> #endif // __ia64__
>
> // int mlock(const void *addr, size_t len);
> _syscall2(int, mlock, const void *, addr, size_t, len )
> // int munlock(const void *addr, size_t len);
> _syscall2(int, munlock, const void *, addr, size_t, len )
> #if !defined(__ia64__)
> #if !defined(__x86_64__)
> // TODO: ia64
> // int modify_ldt(int func, void *ptr, unsigned long bytecount);
> _syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long,
> bytecount )
> #endif
> #endif
> #endif /* FGL_USE_SCT */
> --------------------------

> I actually tried to #define FGL_USE_SCT, but it didn't compile either.
Ok, now I get it... they're trying to workaround the fact that modify_ldt() is 
not exported.

Thus they are probably violating the GPL (well, let's not start anything on 
this), because the syscall table has been unexported on purpose... however 
such tricks will break. I'll add the workaround in next revision, thanks (and 
if I forget, just mail me after the release).
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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[uml-devel] Re: skas3 patch breaks ATI video drivers

[Sven Köhler]

> I.e. the compilation problem is not in the kernel module, right? In this case, 
> the problem is that you have /usr/include/asm symlinked to your kernel's 
> include/asm-i386 directory, which is the wrong setup. However your solution 
> should not give any problem.

Kernel-Modules are usually compiled against the sources in either 
/usr/src/linux or /lib/modules/<version>/build.

Take a look at the nvidia-kernel ebuild or other ebuilds that build 
kernel modules. It would be fatal to compile them against the headers in 
/usr/include. On Gentoo, you can have linux26-headers-2.6.7 installed, 
but actually be running a 2.6.10 Kernel - and even worse, it is even 
possible to keep 2.4 headers when running a 2.6 kernel.



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Re: [uml-devel] Re: skas3 patch breaks ATI video drivers

[Blaisorblade]

On Wednesday 26 January 2005 11:24, Sven Köhler wrote:


Please note this exact sentence:
> > I.e. the compilation problem is not in the kernel module, right?

> > In this 
> > case, the problem is that you have /usr/include/asm symlinked to your
> > kernel's include/asm-i386 directory, which is the wrong setup. However
> > your solution should not give any problem.

> Kernel-Modules are usually compiled against the sources in either
> /usr/src/linux or /lib/modules/<version>/build.

> Take a look at the nvidia-kernel ebuild or other ebuilds that build
> kernel modules. It would be fatal to compile them against the headers in
> /usr/include. On Gentoo, you can have linux26-headers-2.6.7 installed,
> but actually be running a 2.6.10 Kernel - and even worse, it is even
> possible to keep 2.4 headers when running a 2.6 kernel.

Sven, that is clear *and* obvious... what I was *refusing* to believe was that 
a kernel module would be using the "syscall" macro - I explained it by 
thinking it was userspace code.

Maybe that use is even legitimate (1), after all, but it astonished me a bit 
first... and my experience with NVIDIA driver was they also had a userspace 
part to link with X11.

(1) legitimate means "ugly hack which can make sense with non-GPL modules, 
i.e. does not make sense anyway". I'm not flaming ATI / NVIDIA, let's leave 
this duty to people with more spare time.
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Blaisorblade]

On Friday 28 January 2005 15:15, you wrote:
> Hi,
>
> > Ok, now I get it... they're trying to workaround the fact that
> > modify_ldt() is not exported.
> >
> > Thus they are probably violating the GPL

> I am under the impression that it is permitted to distribute a binary
> module, with only the "loader" under GPL.
No, I don't think so... the strict GPL interpretation is that you cannot 
distribute a non-GPL work which links with GPL code...

In fact, distributions cannot distribute GPL code linking with XFree 4.4.

What you probably see is that NVIDIA modules (and ATI ones too I guess, but I 
don't know well) have a binary-only part and a source-code part...

Linux developers mostly consider binary module to be ok until they are not 
"derivative works". And when a symbol is not exported, many times, it is 
because kernel developers feel that code using it is a derivative of the 
kernel.

In this case, it's maybe different - nobody thought that the sys_modify_ldt 
symbol should have been exported. That said, if somebody asked the question, 
the answer could be "No, it must not be exported, because modules using it 
are derivative works". On the other side, any userspace program can call the 
modify_ldt syscall.

> Do you mean that they are actually violating the license,
Well, just a rough feeling... I am not a lawyer.
> or that they 
> are evading the kernel's tainting mechanism?
> I suspect that they want to 
> avoid users getting the message about tainted kernels.
No, users will get the message, unless the module declares it self as "GPL" 
with a "MODULE_LICENSE("GPL") directive in the code, which it should not.
> If so, then I 
> would like to complain to them, because 1) it is disgusting behaviour
> and

> 2) it makes my life more difficult having to take care of their 
> stupid code.
For your specific problem, I'm applying your fix to next version of the SKAS 
patch (which I'm publishing anyway with other work). See my other mail. Not 
that it is a bug of the SKAS patch or of the ATI module alone.

For the GPL issue, you should probably ask to LKML (or post a letter to 
LWN.net about this issue - they could maybe publish it and you'd see the 
comments) or on slashdot.org (which is actually a discussion forum) - I have 
read discussions about such issues, but I'm not myself an expert.
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade


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Re: [uml-devel] skas3 patch breaks ATI video drivers

[Blaisorblade]

[-- Attachment #1: Type: text/plain, Size: 1737 bytes --]

On Monday 24 January 2005 20:43, Marcus Better wrote:
> Hi all,
>
> I applied Blaisorblade's host-skas3-2.6.9-v7.patch, and it breaks the
> fglrx graphics driver from ATI[1]. This is with Debian kernel 2.6.9, but
> I believe it applies to vanilla kernels also.

> The problem is the following declaration added to include/asm-i386/desc.h:

> ----------------------------------------------------------
> extern int modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
>         unsigned long bytecount);
> ----------------------------------------------------------
>
> The fglrx driver contains the following macro in a source file:
>
> _syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long,
> bytecount )
>
> Here the compiler chokes with the following error:
> ---------------------------------------------------------
> /usr/src/modules/fglrx-4.3.0-3.14.6/firegl_public.c:181: error:
> conflicting types for `modify_ldt'
> include/asm/desc.h:144: error: previous declaration of `modify_ldt'
> ---------------------------------------------------------
>
> I don't understand the details of the kernel code, but it seems that the
> problem is that the SKAS patch defines the function modify_ldt which
> conflicts with the syscall macros.
>
> I renamed the new function to _modify_ldt instead (and changed the two
> or three references to it in ldt.c), and this seems to fix the problem.
You should also have modified the reference inside arch/i386/kernel/ptrace.c.

I'm doing compilation-testing of the attached patch, which seems to be good 
(it is not the kind of patch easy to get wrong, however).
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade

[-- Attachment #2: rename-modify-ldt-to-avoid-conflicts.patch --]
[-- Type: text/x-diff, Size: 2501 bytes --]


SKAS adds a function modify_ldt (closely related to sys_modify_ldt) but the
declaration conflicts with some external code (ATI kernel modules). Since the
name is not important, rename the function to __modify_ldt.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

 vanilla-linux-2.6.9-paolo/arch/i386/kernel/ldt.c    |    4 ++--
 vanilla-linux-2.6.9-paolo/arch/i386/kernel/ptrace.c |    2 +-
 vanilla-linux-2.6.9-paolo/include/asm-i386/desc.h   |    2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff -puN include/asm-i386/desc.h~rename-modify-ldt-to-avoid-conflicts include/asm-i386/desc.h
--- vanilla-linux-2.6.9/include/asm-i386/desc.h~rename-modify-ldt-to-avoid-conflicts	2005-01-28 16:23:44.334069944 +0100
+++ vanilla-linux-2.6.9-paolo/include/asm-i386/desc.h	2005-01-28 16:24:48.033386176 +0100
@@ -126,7 +126,7 @@ static inline void load_LDT(mm_context_t
 	put_cpu();
 }
 
-extern int modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
+extern int __modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
 		      unsigned long bytecount);
 
 #endif /* !__ASSEMBLY__ */
diff -puN arch/i386/kernel/ptrace.c~rename-modify-ldt-to-avoid-conflicts arch/i386/kernel/ptrace.c
--- vanilla-linux-2.6.9/arch/i386/kernel/ptrace.c~rename-modify-ldt-to-avoid-conflicts	2005-01-28 16:23:44.407058848 +0100
+++ vanilla-linux-2.6.9-paolo/arch/i386/kernel/ptrace.c	2005-01-28 16:24:48.037385568 +0100
@@ -562,7 +562,7 @@ asmlinkage int sys_ptrace(long request, 
 			ret = -EIO;
 			break;
 		}
-		ret = modify_ldt(child->mm, ldt.func, ldt.ptr, ldt.bytecount);
+		ret = __modify_ldt(child->mm, ldt.func, ldt.ptr, ldt.bytecount);
 		break;
 	}
 
diff -puN arch/i386/kernel/ldt.c~rename-modify-ldt-to-avoid-conflicts arch/i386/kernel/ldt.c
--- vanilla-linux-2.6.9/arch/i386/kernel/ldt.c~rename-modify-ldt-to-avoid-conflicts	2005-01-28 16:23:44.441053680 +0100
+++ vanilla-linux-2.6.9-paolo/arch/i386/kernel/ldt.c	2005-01-28 16:24:48.101375840 +0100
@@ -238,7 +238,7 @@ out:
 	return error;
 }
 
-int modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
+int __modify_ldt(struct mm_struct * mm, int func, void __user *ptr,
 	       unsigned long bytecount)
 {
 	int ret = -ENOSYS;
@@ -262,5 +262,5 @@ int modify_ldt(struct mm_struct * mm, in
 
 asmlinkage int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
 {
-	return modify_ldt(current->mm, func, ptr, bytecount);
+	return __modify_ldt(current->mm, func, ptr, bytecount);
 }
_