[help] _syscall2 fails with -fPIC

[help] _syscall2 fails with -fPIC

[Mark Swanson]

Hello,

I am building a -fPIC shared object that will define and access a Linux
kernel system call, but _syscall2 fails with -fPIC .so compilation.
What can I do?
 
        F.E. the statement:
 
_syscall2 (int, tux, unsigned int, action, user_req_t *, req)
 
Gives the following gcc error when compiled with -fPIC:
 
tst.c: In function `tux':
tst.c:62: Invalid `asm' statement:
tst.c:62: fixed or forbidden register 3 (bx) was spilled for class
BREG.

If the -fPIC isn't there it compiles fine. Unfortunately I need to find
another way as I have to use -fPIC.

Thanks in advance for any suggestions.


=====
A camel is ugly but useful; it may stink, and it may spit, but it'll get you where you're going. - Larry Wall -

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Re: [help] _syscall2 fails with -fPIC

[Ralf Baechle]

On Sat, Feb 17, 2001 at 11:47:09AM -0800, Mark Swanson wrote:

> I am building a -fPIC shared object that will define and access a Linux
> kernel system call, but _syscall2 fails with -fPIC .so compilation.
> What can I do?
>  
>         F.E. the statement:
>  
> _syscall2 (int, tux, unsigned int, action, user_req_t *, req)
>  
> Gives the following gcc error when compiled with -fPIC:
>  
> tst.c: In function `tux':
> tst.c:62: Invalid `asm' statement:
> tst.c:62: fixed or forbidden register 3 (bx) was spilled for class
> BREG.
> 
> If the -fPIC isn't there it compiles fine. Unfortunately I need to find
> another way as I have to use -fPIC.

Don't use the syscallX macros whenever possible; there are all sorts of
portability problems hidden there.  Their primary use is for within the
kernel; any other use should be considered problematic.  The prefered
solution is putting the necessary stubs into libc; if that doesn't seem
to be an option in your case try using the syscall() function defined in
<unistd.h> like:

#include <sys/syscall.h>
#include <unistd.h>

int main(char *argc, char *argv[])
{
	syscall(SYS_write, 1, "Hello, world\n", 13);
}

  Ralf