Re: System calls parameter restrictions


Rafael Almeida wrote:

Are there any restrictions on the parameters that are passed to a
system call? Is it possible to pass a struct as a parameter to a system
call?

Obviously, nobody would design a system that had a system call that
required a parameter you couldn't pass the value for. You can always
pass pointers, otherwise 'read' and 'write' wouldn't work. A struct
would be passed by address.

The _syscall1 macro tries to cast the parameter to a ``long''. Does it
mean that a struct or union type cannot be passed by value? Only as a
pointer?

Mine doesn't cast the parameter to a long. It looks like this:

#define _syscall1(type,name,type1,arg1) \
type name(type1 arg1) \
{\
return syscall(__NR_##name, arg1);\
}

And 'syscall' takes the number of the system call and then '...'.

I believe structs and unions are never passed by value, but I'm not
sure.

DS

.

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