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I did a basic helloWorld system call example that had no parameters and was just:
int main()
{
syscall(__NR_helloWorld);
return 0;
}
But now I am trying to figure out how to pass actual arguments to the system call (ie. a long). What is the format exactly, I tried:
int main()
{
long input = 1;
long result = syscall(__NR_someSysCall, long input, long);
return 0;
}
Where it takes a long and returns a long, but it is not compiling correctly; what is the correct syntax?
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Question: Describe the three general methods used to pass parameters to the OS 1- Pass the parameters in registers 2-Store parameters in a block in memory and address of block passed as a parameter in register 3- Place or push the parameter in a stack then pop off the stack by the operating system The services and ...
When the function is called, the parameter passed to it must be a variable, and that variable's address is passed to the function. Any time the function's body uses the parameter, it uses the variable at the address that was passed. For example, suppose that inc is defined as follows. int w = 1; inc(w);
parameter passing The mechanism used to pass parameters to a procedure (subroutine) or function. The most common methods are to pass the value of the actual parameter (call by value), or to pass the address of the memory location where the actual parameter is stored (call by reference).
Remove the type names. It's just a function call. Example:
#include <sys/syscall.h>
#include <unistd.h>
int main( int argc, char* argv[] ) {
char str[] = "boo\n";
syscall( __NR_write, STDOUT_FILENO, str, sizeof(str) - 1 );
return 0;
}
The prototype for syscall is
#define _GNU_SOURCE /* or _BSD_SOURCE or _SVID_SOURCE */
#include <unistd.h>
#include <sys/syscall.h> /* For SYS_xxx definitions */
int syscall(int number, ...);
This says that it takes a variable number (and type) of parameters. That depends on the particular system call. syscall is not the normal interface to a particular system call. Those can be explicitly coded, for example write(fd, buf, len).
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