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From: Chris Friesen <cfriesen@nortelnetworks.com>
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To: Andreas Schwab <schwab@suse.de>
CC: Benjamin Collar <benjamin.collar@siemens.com>,
       linux-kernel@vger.kernel.org
Subject: Re: PROBLEM: using _syscall4 to call sys_futex with -fPIC won't compile
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Andreas Schwab wrote:
> Benjamin Collar <benjamin.collar@siemens.com> writes:
> 
>  > Greetings
>  >
>  > [1.]
>  > If I use _syscall4 in order to call sys_futex and compile with -fPIC, I
>  > receive this compiler error:
>  > "can't find a register in class `BREG' while reloading `asm'"
> 
> Don't do that then.
> 
>  > [2.]
>  > I'm using futexes in a project and I have to build a shared library;
>  > thus I need to use -fPIC when compiling. When doing so, I get the error
>  > mentioned in [1.].
> 
> Don't use kernel headers in user space.  Use syscall(3) instead.

The "_syscallx" macros are in the userspace versions of the kernel headers, and 
as such should be fair game.  Also, you need to get a list of syscall numbers 
somehow, and those numbers are generally defined in the same file that contains 
the "_syscallx" macros.

syscall() doesn't work for all system calls.  The man page explicitly warns that 
it doesn't work for pipe(2).  Interestingly, the glibc manual doesn't have that 
warning.  Wonder which is correct...

Chris