From: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>,
Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, loongarch@lists.linux.dev,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
linux-s390@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()
Date: Fri, 2 Oct 2026 20:21:47 +0200 [thread overview]
Message-ID: <2618625a-864d-43a4-b151-100e0d76ff87@kernel.org> (raw)
In-Reply-To: <ar-Dx-deXN93M24v@zx2c4.com>
Le 02/10/2026 à 12:13, Jason A. Donenfeld a écrit :
> On Fri, Oct 02, 2026 at 11:49:32AM +0200, Nathan Chancellor wrote:
>> On Thu, Oct 01, 2026 at 01:03:10PM +0200, Nathan Chancellor wrote:
>>> On Thu, Oct 01, 2026 at 12:48:10PM +0200, Jason A. Donenfeld wrote:
>>>> Does this commit seem okay with you? I used the diff you sent below and
>>>> adjusted the commit message: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.zx2c4.com%2Flinux-rng%2Fcommit%2F%3Fid%3D56ff95ee85715047eb5b5220243778af657778c8&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227648970%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=H27VGYLdNkvQiA6l%2BJNnEModMbEySwTMXpLAt8iAFiI%3D&reserved=0
>>>
>>> Yeah, that seems fine to me, thanks for taking care of it!
>>
>> Can you adjust the LLVM value by one from 4294967295 to 4294967294? ~0U
>> is actually a special value, so we hit an assertion in the SystemZ
>> backend.
>>
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fblob%2F3f48e22a1f321d5d3341bd812803694cea588785%2Fllvm%2Flib%2FCodeGen%2FSelectionDAG%2FSelectionDAG.cpp%23L9547&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227670583%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=u8petgY9wU9ur%2By4kaOrb6VFKL%2FNf4tcCIUL%2BcUcDfs%3D&reserved=0
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fblob%2F3f48e22a1f321d5d3341bd812803694cea588785%2Fllvm%2Flib%2FTarget%2FSystemZ%2FSystemZISelLowering.cpp%23L1470-L1471&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227686571%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=cSwt%2BTJdYa%2Bbwe8HyO6FsIq6oU6YNplRlwCa0upif9Q%3D&reserved=0
>>
>> clang: llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:1471: virtual bool llvm::SystemZTargetLowering::findOptimalMemOpLowering(LLVMContext &, std::vector<EVT> &, unsigned int, const MemOp &, unsigned int, unsigned int, const AttributeList &, EVT *) const: Assertion `Limit != ~0U && "Expected EmitTargetCodeForMemXXX() to handle AlwaysInline cases."' failed.
>> PLEASE submit a bug report to https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fissues%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227701575%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=%2F3q8laZb%2FDhCWp117N9EtyxLIc5lq%2FzEN2l0z%2BXwDHY%3D&reserved=0 and include the crash backtrace and dumped files.
>> Stack dump:
>> 0. Program arguments: ...
>> 1. <eof> parser at end of file
>> 2. Code generation
>> 3. Running pass 'Function Pass Manager' on module 'arch/s390/kernel/vdso/vgetrandom.c'.
>> 4. Running pass 'SystemZ DAG->DAG Pattern Instruction Selection' on function '@__kernel_getrandom'
>> ...
>
> Holy smokes. Sure, fixed: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.zx2c4.com%2Flinux-rng%2Fcommit%2F%3Fid%3Deb13a1ff271b0d180687eebb30611b0b276d5193&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227716550%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=WcnFE6S72OrDTNNvU1T06BtUTyI1sDx%2F%2Btz%2FkpGslMA%3D&reserved=0
>
>
> From eb13a1ff271b0d180687eebb30611b0b276d5193 Mon Sep 17 00:00:00 2001
> From: Nathan Chancellor <nathan@kernel.org>
> Date: Fri, 25 Sep 2026 22:46:32 +0100
> Subject: [PATCH] random: vDSO: avoid call to memset() when zeroing reserved
> parameter
>
> After a recent change in LLVM [1], builds with the random vDSO
> implementation, such as PowerPC and RISC-V, fail when checking the vDSO:
>
> arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
> arch/riscv/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported
>
> memset() is now generated when zeroing params->reserved for some builds
> because LLVM has an optimization (now run in more instances) that can
> recognize at compile time when it is assigning a static value to a
> contiguous area of memory and turn that into a call to memset(). Both
> clang and GCC assume memset() is always available [2].
>
> Clang has an internal fiddly hook, -max-store-memset, which we can set
> to a high number, to disable generating out of line memset calls [3].
> Similarly, GCC has -finline-stringops=memset to do the same [4], should
> this issue ever hit future version of GCC. While these options wouldn't
> make sense for normal kernel code, it is fine for the extremely limited
> and intentionally compact vDSO code.
>
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2F90cebef1411617fc3eedd359bdf00cb44b1c2439&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227732238%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=cYZ2nUalY%2F6yarydfMIlcGpDVlztXRBeg7UG7tpCO9g%3D&reserved=0 [1]
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc-16.2.0%2Fgcc%2FStandards.html%23index-ffreestanding&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227748542%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=vRl%2BQgL5GJ0wowXAIlRIczC5XqUXyOFUvFVe5C8XWAc%3D&reserved=0 [2]
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2Fb28eeb28bea39148738dc375e8a97072a1907e64&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227762721%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=nt59J3%2BOoiEKYGzfFfAq7WoAnEMAimt6vKDaJjhvHtg%3D&reserved=0 [3]
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc%2FOptimize-Options.html%23index-finline-stringops&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227777215%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=fyZA9XC%2FwSAUc346VWT%2FmyeqddqeTo62dBKtiJilR9U%3D&reserved=0 [4]
> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F2183&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4caf8956c2d94439c19a08df206dd40b%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639265328227792263%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=49HfUDlzn%2FLUeISQ7%2BFR5jE7lZkqfORaqjauLn8cdm0%3D&reserved=0
> Cc: stable@vger.kernel.org # v6.12+
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Ok, I checked the version that is in the rng tree, namely commit
eb13a1ff271b ("random: vDSO: avoid call to memset() when zeroing
reserved parameter"). Looks similar to this mail.
It looks ok, no change to generated loop on powerpc32 neither with gcc
13 nor gcc 16.
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
> ---
> arch/arm64/kernel/vdso/Makefile | 2 +-
> arch/loongarch/vdso/Makefile | 1 +
> arch/powerpc/kernel/vdso/Makefile | 1 +
> arch/riscv/kernel/vdso/Makefile | 1 +
> arch/s390/kernel/vdso/Makefile | 1 +
> arch/x86/entry/vdso/vdso64/Makefile | 2 +-
> init/Kconfig | 5 +++++
> 7 files changed, 11 insertions(+), 2 deletions(-)
>
next prev parent reply other threads:[~2026-10-02 18:22 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-25 21:46 Nathan Chancellor
2026-09-25 21:53 ` Nick Desaulniers
2026-09-25 21:56 ` Nick Desaulniers
2026-09-25 22:00 ` Nick Desaulniers
2026-09-25 22:19 ` Nathan Chancellor
2026-09-26 6:34 ` Christophe Leroy (CS GROUP)
2026-09-26 10:02 ` Jason A. Donenfeld
2026-09-26 10:55 ` Christophe Leroy (CS GROUP)
2026-09-26 12:29 ` Jason A. Donenfeld
2026-09-29 18:24 ` Nick Desaulniers
2026-09-30 13:38 ` Nathan Chancellor
2026-09-30 14:21 ` Jason A. Donenfeld
2026-09-30 14:44 ` Jason A. Donenfeld
2026-09-30 15:13 ` Nathan Chancellor
2026-09-30 15:16 ` Jason A. Donenfeld
2026-10-01 4:41 ` Christophe Leroy (CS GROUP)
2026-10-01 9:25 ` Jason A. Donenfeld
2026-10-01 10:20 ` Nathan Chancellor
2026-10-01 10:48 ` Jason A. Donenfeld
2026-10-01 11:03 ` Nathan Chancellor
2026-10-02 9:49 ` Nathan Chancellor
2026-10-02 10:13 ` Jason A. Donenfeld
2026-10-02 18:21 ` Christophe Leroy (CS GROUP) [this message]
2026-10-02 9:18 ` Christophe Leroy (CS GROUP)
2026-10-02 9:27 ` Jason A. Donenfeld
2026-09-26 12:39 ` Nathan Chancellor
2026-09-26 9:39 ` Andreas Schwab
2026-09-26 12:19 ` Nathan Chancellor
2026-09-26 12:32 ` Jason A. Donenfeld
2026-09-26 12:49 ` Nathan Chancellor
2026-09-27 7:02 ` David Laight
2026-09-29 16:59 ` Nathan Chancellor
2026-09-29 17:44 ` David Laight
2026-10-02 10:57 ` Christophe Leroy (CS GROUP)
2026-10-02 10:58 ` Jason A. Donenfeld
2026-10-02 11:01 ` LEROY Christophe
2026-10-02 11:02 ` Christophe Leroy (CS GROUP)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2618625a-864d-43a4-b151-100e0d76ff87@kernel.org \
--to=chleroy@kernel.org \
--cc=Jason@zx2c4.com \
--cc=agordeev@linux.ibm.com \
--cc=alex@ghiti.fr \
--cc=aou@eecs.berkeley.edu \
--cc=borntraeger@linux.ibm.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=chenhuacai@kernel.org \
--cc=dave.hansen@linux.intel.com \
--cc=gor@linux.ibm.com \
--cc=hca@linux.ibm.com \
--cc=hpa@zytor.com \
--cc=justinstitt@google.com \
--cc=kernel@xen0n.name \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=linux-s390@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=llvm@lists.linux.dev \
--cc=loongarch@lists.linux.dev \
--cc=luto@kernel.org \
--cc=maddy@linux.ibm.com \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=morbo@google.com \
--cc=mpe@ellerman.id.au \
--cc=nathan@kernel.org \
--cc=ndesaulniers@google.com \
--cc=npiggin@gmail.com \
--cc=palmer@dabbelt.com \
--cc=pjw@kernel.org \
--cc=svens@linux.ibm.com \
--cc=tglx@kernel.org \
--cc=tytso@mit.edu \
--cc=vincenzo.frascino@arm.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®