Received-SPF: pass (google.com: domain of linux-kernel+bounces-205759-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <28c74739-e775-4813-b2f1-b588e14b3674@rasmusvillemoes.dk>
Date: Fri, 7 Jun 2024 11:52:47 +0200
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: objtool query: section start/end symbols?
To: Linus Torvalds <torvalds@linux-foundation.org>,
 Josh Poimboeuf <jpoimboe@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <CAHk-=wjHf6C_74VQPxmge-sMmu5yuhmNor1TaO0Uq--zrA13HA@mail.gmail.com>
Content-Language: en-US, da
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
In-Reply-To: <CAHk-=wjHf6C_74VQPxmge-sMmu5yuhmNor1TaO0Uq--zrA13HA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

On 06/06/2024 20.42, Linus Torvalds wrote:
> So this is related to my currently very ugly hack at
> 
>    https://lore.kernel.org/all/CAHk-=whFSz=usMPHHGAQBnJRVAFfuH4gFHtgyLe0YET75zYRzA@mail.gmail.com/
> 
> where I'm trying to do "runtime constants". 

FWIW, I did a POC some years ago but either never managed to send it, or
never got a response. It did boot in virtme and I managed to get gdb to
do disassembly to show that the dentry hash lookup did become a 'shift
immediate'.

https://github.com/Villemoes/linux/tree/rai

IIRC, I didn't bother with updating users when the boottime value was
settled, but just had a single at-the-end-of-init call to update all
sites; in the meantime, use sites were implemented as a jump to a piece
of code that did the dynamic load of the constants.

Rasmus