Subject: Re: COMPAT_LINUX vsyscall
To: None <>
From: Christos Zoulas <>
List: tech-kern
Date: 05/01/2005 12:21:42
In article <>,
Emmanuel Dreyfus <> wrote:
>Working on COMPAT_LINUX, I discovered a new Linux feature (kernel
> called the vsyscall page. This is similar to Darwin's
>commpage: a page of functions mapped by the kernel in userspace:
>Here is pmap output when stopped by a breakpoint after the program
>first's instruction:
>0000000000400000    436K r-x--  /home/manu/tests/hello
>000000000056c000     40K rw---  /home/manu/tests/hello
>0000000000576000      8K rw---    [ anon ]
>00007ffffffeb000     84K rw---    [ stack ]
>ffffffffff600000   8192K -----    [ anon ] 
>If I disasseble the first bytes, it looks like a gettimeofday() system
>call (on Linux/amd64, syscall 0x60 is gettimeofday)
>0xffffffffff600000:     mov    426(%rip),%eax
>0xffffffffff600006:     push   %rbx
>0xffffffffff600007:     test   %eax,%eax
>0xffffffffff600009:     jne    0xffffffffff600017
>0xffffffffff60000b:     mov    $0x60,%eax
>0xffffffffff600010:     syscall 
>Someone already had a look at it? I'd like to not rediscover the wheel
>by groveling in Linux sources.

No, this wheel is all yours :-) And while you are spinning it, it would
be nice to have this facility or similar in NetBSD.