linux-kernel - Re: [RFC 08/19] exec: add API specification for execve

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Message-ID: <87y0tqu9g7.fsf@oldenburg.str.redhat.com>
Date: Tue, 17 Jun 2025 09:13:44 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org,  linux-api@...r.kernel.org,
  workflows@...r.kernel.org,  tools@...nel.org
Subject: Re: [RFC 08/19] exec: add API specification for execve

* Sasha Levin:

> On Mon, Jun 16, 2025 at 11:39:31PM +0200, Florian Weimer wrote:
>>* Sasha Levin:
>>
>>> +	KAPI_RETURN("long", "Does not return on success; returns -1 on error")
>>> +		.type = KAPI_TYPE_INT,
>>> +		.check_type = KAPI_RETURN_ERROR_CHECK,
>>> +	KAPI_RETURN_END
>>
>>Is the -1 part correct?
>
> Maybe :) That's one of the things I wasn't sure about: we're documenting
> the execve syscall rather than the function itself. A user calling
> execve() will end up with -1 on failure, and errno set with the error
> code.

Well, it doesn't say execve, it says sys_execve.

> You could argue that it's libc that sets errno and we're trying to spec
> the kernel here, not the userspace interface to it.

And I think this would be appropriate.

Note that in the future, the glibc version of execve will not be a
straightforward system call wrapper because we need to obtain a
consistent snapshot of the environment array.  That is actually pretty
hard because we cannot atomically replace the process image, unblock
signals, and unmap a copy of the environment.

So I think it's best for the kernel to stick with the system call
interface and not try to document what libcs are doing.

An even more thorny example are the setuid family of system calls, where
the kernel is extremely far away from what POSIX requires, and we have
to fix it in userspace.

Thanks,
Florian