From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Josh Poimboeuf" <jpoimboe@kernel.org>,
"Nathan Chancellor" <nathan@kernel.org>,
"Nicolas Schier" <nsc@kernel.org>,
"Nick Desaulniers" <ndesaulniers@google.com>,
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"Justin Stitt" <justinstitt@google.com>,
"Masahiro Yamada" <masahiroy@kernel.org>,
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"Thomas Gleixner" <tglx@kernel.org>,
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"Palmer Dabbelt" <palmer@dabbelt.com>,
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"Tamir Duberstein" <tamird@kernel.org>,
"Alexandre Courbot" <acourbot@nvidia.com>,
"Onur Özkan" <work@onurozkan.dev>,
"Jonathan Corbet" <corbet@lwn.net>,
"Randy Dunlap" <rdunlap@infradead.org>,
"Kees Cook" <kees@kernel.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
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linux-efi@vger.kernel.org, rust-for-linux@vger.kernel.org,
linux-doc@vger.kernel.org, "Jens Axboe" <axboe@kernel.dk>,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 15/21] objtool: cache relocations, do less work
Date: Tue, 15 Sep 2026 13:24:17 +0100 [thread overview]
Message-ID: <aqk4Oani0H0Wpxs1@gremlin> (raw)
In-Reply-To: <CAHk-=wj3BKkCYtmfs5sORF_+Oumv2Gc8D+YxkMp9W2-mvLS=Ug@mail.gmail.com>
On Mon, Sep 14, 2026 at 03:30:19PM -0700, Linus Torvalds wrote:
> On Mon, 14 Sept 2026 at 15:23, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> >
> > There might be more efficient ways to structure the considerable amount
> > of data, like replacing "struct instruction" with "struct basic_block"
> > or so, but it's hard to know whether that would be a net positive.
>
> Yeah, I was thinking that you'd only hash instructions as you find
> them if they are obvious "I need this instruction", and then try to
> hash them *again* if they are branch targets (and just have a "already
> hashed" flag).
>
> That way random number instructions would not be on the hash - unless
> they become branch targets.
>
> And you wouldn't ever really have to track any complicated decisions
> (like that whole "basic block" thing - I agree that it's painful,
> because the shape of a basic block will change over time as you find
> branch targets).
>
> But not a big deal. More an idle thought brought on by that other
> patch that changed the hash table size, and this discussion that was
> talking about the hashing - or not hashing - of sections.
>
> So more of a "if it is easy and straightforward" kind of thing.
Obviously I defer to Josh on this, but it seems from what he said it's
probably a little involved and maybe tricky to figure out how much impact
it might have.
Anyway v3 drops the relocation hash altogether so 1 out of 2 ain't bad ;)
>
> Linus
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-09-15 12:24 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 01/21] kbuild: do not allocate .modinfo in vmlinux Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 02/21] kallsyms: index symbols by token to speed up table compression Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly Lorenzo Stoakes (ARM)
2026-09-14 20:16 ` Markus Elfring
2026-09-14 21:44 ` David Laight
2026-09-15 7:10 ` [v2 " Markus Elfring
2026-09-14 9:22 ` [PATCH v2 04/21] kbuild: do not sort nm output where the order is irrelevant Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 05/21] kbuild: only emit vmlinux relocations when required Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 06/21] elf-parse: add section flags, symbol binding and a read-only mapping Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
2026-09-14 16:33 ` Markus Elfring
2026-09-14 16:54 ` Markus Elfring
2026-09-14 17:01 ` Markus Elfring
2026-09-14 9:22 ` [PATCH v2 08/21] kbuild: cache list, composite object state per object Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 09/21] kbuild: implement and use depcheck to check dependency timestamps Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 10/21] kbuild: move the toolchain checks into init/Kconfig.toolchain Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes Lorenzo Stoakes (ARM)
2026-09-14 15:02 ` John Stoffel
2026-09-14 15:24 ` Lorenzo Stoakes (ARM)
2026-09-15 11:01 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 12/21] modpost: cache section relocation mismatch state Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 13/21] modpost: emit module descriptors as assembly Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 14/21] kbuild: batch module finalisation Lorenzo Stoakes (ARM)
2026-09-14 18:00 ` Kees Cook
2026-09-15 10:44 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 15/21] objtool: cache relocations, do less work Lorenzo Stoakes (ARM)
2026-09-14 19:44 ` Josh Poimboeuf
2026-09-14 20:06 ` Linus Torvalds
2026-09-14 22:23 ` Josh Poimboeuf
2026-09-14 22:30 ` Linus Torvalds
2026-09-15 12:24 ` Lorenzo Stoakes (ARM) [this message]
2026-09-15 12:19 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 16/21] objtool: size the instruction hash to the text Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel Lorenzo Stoakes (ARM)
2026-09-14 18:20 ` Kees Cook
2026-09-15 10:09 ` Lorenzo Stoakes (ARM)
2026-09-15 11:29 ` David Laight
2026-09-14 9:22 ` [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Lorenzo Stoakes (ARM)
2026-09-14 18:32 ` Kees Cook
2026-09-15 11:09 ` Lorenzo Stoakes (ARM)
2026-09-15 11:16 ` Lorenzo Stoakes (ARM)
2026-09-15 6:32 ` Miguel Ojeda
2026-09-15 11:15 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 19/21] rust: make exports.o depend on the headers generated for it Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build Lorenzo Stoakes (ARM)
2026-09-14 18:37 ` Kees Cook
2026-09-15 11:58 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 21/21] kbuild: use pigz for gzip compression if available Lorenzo Stoakes (ARM)
2026-09-14 16:39 ` Kees Cook
2026-09-14 16:49 ` H. Peter Anvin
2026-09-14 17:50 ` Kees Cook
2026-09-15 14:30 ` Lorenzo Stoakes (ARM)
2026-09-14 15:41 ` [PATCH v2 00/21] kbuild: significantly speed up kernel builds Kees Cook
2026-09-14 15:53 ` Linus Torvalds
2026-09-15 8:53 ` Arnd Bergmann
2026-09-15 11:35 ` Lorenzo Stoakes (ARM)
2026-09-14 18:25 ` Lorenzo Stoakes (ARM)
2026-09-14 18:43 ` Kees Cook
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