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

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

On 11/6/24 21:30, Noah Goldstein wrote:
> On Wed, Nov 6, 2024 at 3:10 PM Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> On 11/6/24 18:13, Noah Goldstein wrote:
>>> Question about impl regarding handling of `-execfd` with/without a program name.
>>>
>>> 1) `-execfd` + program name ie: `qemu -execfd <some_fd> ls -a`.
>>> 2) `-execfd` without program name i.e: `qemu -execfd <some_fd> -a`.
>>>
>>> Do you want to allow both of these? If you want to allow (1), what should
>>> we use for `argv[0]`/`exec_path`. The program pass ("ls") or
>>> `readlink(<some_fd>)`?
>>
>> The canonical response is, examine the kernel source.
>> We're not implementing this in a vacuum, you're replicating execveat(2).
>>
>> I suspect the answer is (1), to be compared with
>>
>>       syscall(__NR_execveat, some_fd, "", &["ls", "-a"], env, AT_EMPTY_PATH);
> 
> Err, I think the reference for '-execfd' is `fexecve`:
> https://man7.org/linux/man-pages/man3/fexecve.3.html

No, fexecve(3) is a glibc function which (nowadays) uses the execveat(2) syscall that we 
want to emulate.

> Which doesn't take a path...

... corresponding to the "" and AT_EMPTY_PATH above.

> So I guess we just interpret the "ls" as argv[0] but not as "exec_path".

But your conclusion is correct.


r~