Re: linux-user: Add option to run `execve`d programs through QEMU

[Richard Henderson <richard.henderson@linaro.org>]

On 11/5/24 23:54, Noah Goldstein wrote:
>>> You still need to handle is_proc_myself, for the guest binary.
> 
> Would this by handled by basically do:
> 
> ```
> if (is_proc_myself(p, "exe")) {
>          exe = exec_path;
>          if (through_qemu)
>              argp[argp_offset] = exec_path;
> }
> ```
> Or am I missing something?

Something like that, yes.

>>> I wonder if those two cases are related.  Do we need to also add an argument so that we
>>> can pass the executable to the next qemu via file descriptor?  I.e. execvat becomes
>>>
>>>       f = openat()
>>>       execv(qemu, "-execfd", f)
>>>
>>> and is_proc_myself uses execfd, which we already have open.
> 
> How does passing a fd from one process to another work?
As long as the fd is not marked O_CLOEXEC, it stays open in the new process.  Providing 
the number via command-line, or whatever, is sufficient for the new process to know what 
is going on.

I now realize this is necessary for the AT_EMPTY_PATH flag, where we only have the file 
descriptor.


r~