Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix get_nr_restart_syscall()

[Andy Lutomirski]

> On Nov 29, 2019, at 9:32 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> 
> ïOn 11/28, Andy Lutomirski wrote:
>> 
>> I think this doesnât work for x32.
> 
> Why? get_nr_restart_syscall() can still rely on the "orig_ax & __X32_SYSCALL_BIT"
> check, debugger should restore regs->orig_ax correctly.

Right. Although relying on this is IMO a ridiculous bit of ABI.

> 
>> Letâs either save the result of syscall_get_arch()
> 
> We can save the result of syscall_get_arch(), but it doesn't distinguish
> x32/x86_64 tasks, so it doesn't really differ from TS_COMPAT.

Duh. Never mind.

> 
>> or just actually calculate and save the restart_syscall nr here.
> 
> sure, we we can do this.

I like this the best unless we can renumber the syscalls.

> 
>> Before we commit to this, Kees, do you think we can manage to just renumber
>> restart_syscall()?  Thatâs a much better solution if we can pull it off.
> 
> Agreed.
> 
> Oleg.
>