Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

Al Viro
2011-08-22T02:08:05Z

On Sun, Aug 21, 2011 at 10:01:40PM -0400, Andrew Lutomirski wrote:

> 3. We're worried that pt_regs-using compat syscalls might want the
> regs to appear to match the actual arguments (why?)

run strace and you'll see why.

> 4. ptrace expects the "registers" when SYSCALL happens to match the
> int 0x80 convention. (This is, IMO, sick.)

That's what ptrace is *for*. It's there to let debuggers play with
the program being debugged, including taking a look at the syscall
arguments and modifying them. In a predictable way, please.