The location is part of the kernel ABI contract with userland I think, and can probably never change (not super familiar with Linux compatibility promises though). As for location I think it's always at the start of the stack, which starts at the highest addressable address minus one guard page (I think). 

From: Corentin Jabot <corentinjabot@gmail.com>
Sent: Friday, July 30, 2021 9:02:04 AM
To: Tom Honermann <tom@honermann.net>
Cc: SG16 <sg16@lists.isocpp.org>; Charlie Barto <Charles.Barto@microsoft.com>; Thiago Macieira <thiago@macieira.org>
Subject: Re: [SG16] A UTF-8 environment specification; an alternative to assuming UTF-8 based on choice of literal encoding
 


On Fri, Jul 30, 2021 at 5:41 PM Tom Honermann <tom@honermann.net> wrote:
On 7/30/21 10:56 AM, Thiago Macieira via SG16 wrote:
> On Thursday, 29 July 2021 19:11:03 PDT Charlie Barto wrote:
>> If such functionality were to be added it would be neat if the linux
>> implementations worked even if procfs were not mounted (such as when the
>> process is init) unless I'm mistaken fetching the command line through proc
>> for your own process is making like two system calls to de-reference a
>> pointer into your own address space.
> Going off-topic here, but correcting the above.
> Procfs is not required for one's own command-line and environment in any Unix
> I know of. They are duplicated in Linux's /proc, but they are added to the
> process' virtual address space just above the stack (and below the auxv).

True today, but I suspect their location is subject to change (though
probably unlikely).

Is there a straight forward way to determine their location in memory?

Do we need to?

It seems like a robust (yet painful) solution would be to ask the language below (c folks) to make this happen
(When glibc calls main it can put argv in a global)
 
 
Tom.

>
> Trivia: if you modify that area, the /proc files also change, allowing you to
> change the name presented in ps and similar tools.
>
> $ ps -o pid,command -Cfile.so
>      PID COMMAND
>     4873 file.so [kdeinit5] file local:/run/user/1000/klauncherdAEtky.1.slave-
> socket local:/run/user/1000/kded5hvkirU.1.slave-socket
>     4874 file.so [kdeinit5] file local:/run/user/1000/klauncherdAEtky.1.slave-
> socket local:/run/user/1000/kded5FwKgfB.2.slave-socket
>