On 11/6/24 17:03, Noah Goldstein wrote:
On Wed, Nov 6, 2024 at 3:38 AM Richard Henderson
<richard.hender...@linaro.org> wrote:
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.
Err I guess I was thinking its a bit weird having an option that is
only really applicable
if qemu is a child process. I.e the `-execfd` argument is not usable
from commandline.
qemu-foo -execfd 3 3< /some/file
Or perhaps opened via other tooling.
I now realize this is necessary for the AT_EMPTY_PATH flag, where we only have
the file
descriptor.
We could also do something along the lines of:
```
fd = openat(dirfd, exe);
char new_exe[PATH_MAX];
char fd_path[PATH_MAX];
sprintf(fd_path, "/proc/self/fd/%d", fd);
readlink(fd_path, new_exe, PATH_MAX);
Reading the link doesn't always work.
Reading or passing the link means AT_SYMLINK_NOFOLLOW isn't honored.
r~
