linux-kernel - Re: objtool query: section start/end symbols?

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Date: Fri, 7 Jun 2024 11:52:47 +0200
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: objtool query: section start/end symbols?

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