Re: Calling syscalls from x86-64 kernel results in a crash on Opteron machines

[Brian Gerst <bgerst@didntduck.org>]

Constantine Gavrilov wrote:

> Christoph Hellwig wrote:
> 
>> On Mon, Sep 13, 2004 at 05:04:17PM +0300, Constantine Gavrilov wrote:
>>  
>>
>>> Hello:
>>>
>>> We have a piece of kernel code that calls some system calls in kernel 
>>> context (
>>>   
>>
>>
>> Which you shouldn't do in the first place.
>>  
>>
> 
> Function kernel_thread() on i386 is implemented by putting the args to 
> appropriate regs and calling int 0x80, resulting in a system call 
> clone() on i386.

It's gone in 2.6, in favor of calling do_fork() directly.

> I have also found the "syscall" instruction in x86-64 kernel specific 
> code (it does not call _syscall() macros directly, though). So, 
> "shouldn't do" is a bit too strong.
> 
> What I am writing is an application, and not interface. As such, it is 
> not much different from its requierements from a user-space application. 
> If user-space application may call system calls, why a kernel space 
> application cannot?
> 
> And BTW, kernel-space applications have their own place even if the 
> concept seems foreign to you.

What are you trying to do that can't be done in user space?  The only 
possible reason for a kernel space app is for performance (like knfsd), 
at the cost of risking system stability and security.

--
				Brian Gerst