But, if your passing parameters to syscall and syscall doesn't know what to do with them then the behavior is undefined. Undefined means anything could happen, data corruption, crash and etc. The problem is that Perl has to make assumptions about what you are going to do inside the syscall without actually parsing the syscall.

From perldoc -f syscall:

"You can't use a string literal(or other read-only string) as an argument to "syscall" because Perl has to assume that any string pointer might be written through."

We can't expect the same kind of DWIM inside the syscall as we ususally expect elsewhere from Perl. Instead Perl 'expects' our parameter to match syscall.ph. Any thing else is going to give undefined behaviors.

I don't know if Perl is trying to prep the string for writing as above or if the closing is accidental.