I looked through book about writing kernel modules in Linux (actually it's in russian lang). It's oriented on x86 architecture. I fount some not so real but interesting sample with syscall from inline assmebler code and port it to arm architecture. I used codesourcery toolchain.

Some information about arm syscalls in linux. According ARM EABI one use r7 register for syscall number and swi 0 (or svc 0, codesourcery gcc generate the same code) for syscall. One can use also r0-r5 registers for 32 bit parameters (or r0...r6 for 64 bit parameters, but them must be aligned to even number of registers)


+++++++++++++++++[syscall.c]++++++++++++++++++++++++++

.....
static int write_call(char* buf, int n )
{
volatile int block[2];
block[0] = (int)buf;
block[1] = n;

__asm__ volatile (
"mov r0, #1\n\t" /* stdout */
"ldr r1, [%0]\n\t" /* buf */
"ldr r2, [%0, #4]\n\t" /* n */
"mov r7, #4\n\t" /* __NR_write */
"svc 0x0\n" /* write() */
"str r0, [%0]\n\t"
:
: "r" (block)
: "r0","r1","r2","r7"
);
if (block[0] < 0)
block[0] = -1;

return block[0];
}

void do_write( void ) {
char *str = "write syscall string!\n";
int len = strlen( str ) + 1, n;
printf( "string for write length = %d\n", len );
n = write_call(str, len);
printf( "write return :%d\n", n );
}
.......
+++++++++++++++++++++++++++++++++++++++++++

++++++++++++++[ Makefile ]+++++++++++++++++++++
CC=arm-none-linux-gnueabi-gcc

syscall: syscall.c
$(CC) $^ -o syscall

clean:
rm -f syscall core
+++++++++++++++++++++++++++++++++++++++++++

Some information about ARM toolchain from codesourcery from IBM. Also I used valgrind source. For further information about ARM inline assembler one can use this source.