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Fri, 19 Jun 2026 09:52:40 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: A0Y27BypNIT- Date: Fri, 19 Jun 2026 15:52:20 +0200 From: "Arnd Bergmann" To: "Will Deacon" , linux-arm-kernel@lists.infradead.org Cc: "Nick Desaulniers" , "Steffen Eiden" , "Andreas Grapentin" , "Catalin Marinas" , "Dave Martin" , "Mark Rutland" , "Marc Zyngier" Message-Id: <8549526e-aff5-4448-b673-dbba7ed9065c@app.fastmail.com> In-Reply-To: <20260619130835.5678-1-will@kernel.org> References: <20260619130835.5678-1-will@kernel.org> Subject: Re: [PATCH] arm64: uapi: Use __u128 instead of __uint128_t in UAPI headers Content-Type: text/plain Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260619_065244_450775_0C004B87 X-CRM114-Status: GOOD ( 13.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jun 19, 2026, at 15:08, Will Deacon wrote: > The arm64 UAPI exposes '__uint128_t' types in the members of > 'struct user_fpsimd_state', 'struct user_pac_address_keys' and in the > signal frame via 'struct fpsimd_context'. Since the alignment of such > a type appears to be non-portable (16 bytes on arm64, 8 bytes on s390), > prefer the '__u128' typedef from uapi/linux/types.h, which makes the > alignment explicit and allows the definitions to be reused by other > host architectures. > > Cc: Arnd Bergmann > Cc: Nick Desaulniers > Cc: Steffen Eiden > Cc: Andreas Grapentin > Cc: Catalin Marinas > Cc: Dave Martin > Cc: Mark Rutland > Cc: Marc Zyngier > Signed-off-by: Will Deacon Reviewed-by: Arnd Bergmann > I think it's a straightforward change, but the only thing that makes me > pause for thought is whether there are toolchains out there which accept > __uint128_t but not __int128. Then again, if that crops up as an issue > we can probably just tweak the typedef we have in uapi/linux/types.h. clang-3.1 and gcc-4.6 support both and are 15 years old, older versions only do __uint128_t. I agree that this should be fine. Arnd