Is the immediate value used in the SVC instruction.
It is an expression evaluating to an integer in the range:
0 to 224-1 (a 24-bit value) in an ARM instruction
0-255 (an 8-bit value) in a 16-bit Thumb instruction.
real_num
Is the value passed in r12 to the handler to determine the function to perform.
To use the indirect mechanism, your system handlers must make use of the r12 value to select the required operation.
Usage
You can use this feature to implement indirect SVCs.
Example
int __svc_indirect(0) ioctl(int svcino, int fn, void *argp);
Calling:
ioctl(IOCTL+4, RESET, NULL);
compiles to SVC #0 with IOCTL+4 in r12.
Errors
When an ARM architecture variant or ARM architecture-based processor that does not support an SVC instruction is specified on the command line using the --cpu option, the compiler generates an error.