There is problem when calling generic syscall() function on 64-bit architectures. The return value is clamped to 32 bits.

Can be reproduced with mmap or mremap syscalls:

> #!/usr/bin/perl -w
> use strict;
>
> sub find_vdso()
> {
>       open my $maps, '<', '/proc/self/maps' or die;
>       /^(.*?)-.*\[vdso\]$/ and return hex $1 for <$maps>;
> }
> 
> my $vdso_addr = find_vdso || die 'not 64-bit linux?';
>
> my $ret = syscall 25,         # __NR_mremap
>               $vdso_addr,     # old_addr
>               1,              # old_len
>               1,              # new_len
>               0,              # flags
>               0;              # new_addr (unused)
>
> $ret == $vdso_addr or die "FAILED\n";

Fixed in upstream commit:

commit f9344c91a4ca48288bba30dc94a2d712d0659670
Author: Oleg Nesterov <oleg>
Date:   Wed Jul 4 08:21:15 2012 -0700

    [perl #113980] pp_syscall: "I32 retval" truncates the returned value
    
    I noticed today that syscall(9, ...) (mmap) doesn't work for me.
    
    The problem is obvious, pp_syscall() uses I32 for retval and the
    "long" address doesn't fit into "int".
    
    The one-liner below should fix the problem.