From nobody Thu Apr 9 06:36:02 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6DCCB389DF0; Tue, 10 Mar 2026 11:50:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773143448; cv=none; b=rOieYG+6FWSf8F9/6Hy2+u39cLuiT/pcFZU+fpVCX5U0AXnP22DcTHBqix37sNUNcgZfNye25k4gYKtqwdcls7P4R4i3yFT+17/wr+asiyaRhyL4hPQiaLHdt63wgsyyA5F8zhpUiyczPsFbDM4KpqPISkVPgSn5DJXQRkcN6Cw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773143448; c=relaxed/simple; bh=rkBx+y3DCrBvqT+9OS2bCaB+okZjtbl0U6cBxknMQg8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=TKelXEdDuSJcksTSSZU14hIvjg8cWCQk/hMo6i93DDfcBcogBAV+HfqTdFhYgfWtTVEYBa9LfzJxF6KNYGnqCnCI5LP6FYDxPJGzNuQDLeyNu93i7m4ajkDdHYTTrOZ7OI4LAZCCJ9bt6sIgh+PktFd8vU55+BZhZs9jM+TGQ1I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YhmI2pYI; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YhmI2pYI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BEC59C2BC9E; Tue, 10 Mar 2026 11:50:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773143447; bh=rkBx+y3DCrBvqT+9OS2bCaB+okZjtbl0U6cBxknMQg8=; h=From:Date:Subject:To:Cc:From; b=YhmI2pYIOQdGl5Il9FVR+Sli0AECmdZMdYyCTmqcfGEc5c6cOyDOQjR5LVqjzNQDa Jg+J9RKTp2fGDnxtNeYnRjTTpsfJRIlZQlL74nisnx/RyOJ1BATsj/6LujzLJC1j71 DL5gdOI98iIre6yNbyGkrTfTk9a6FdPXD0TKW1ckbfppkOWJa319SUK4nnQpB51QsH C0T4O4eJFJXJEKzKmePpDq6ox8bEP/dMf/1GaoBlVoLPrlfgX0TjAHHzFdKgECGlDP c6w3SQtKXgQS8B/hFBa5WS0wYRdgs4eAVWyUClG4opsLI2fJP+ZO9WCjrWOb1lxzR9 mE9rztf1OrcXA== From: Daniel Gomez Date: Tue, 10 Mar 2026 12:50:40 +0100 Subject: [PATCH v2] Documentation/kbuild: fix empty string KBUILD_BUILD_TIMESTAMP Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260310-fix-llvm-docs-v2-1-5e52173aabc7@samsung.com> X-B4-Tracking: v=1; b=H4sIAI8FsGkC/3WMQQ7CIBBFr9LM2jEMbQq68h6mi4bSlqSAYZRoG u4udu/y/fz3dmCbnGW4Njskmx27GCrIUwNmHcNi0U2VQQrZi5YEzu6N25Y9TtEw0nwhQ9aoXmi oziPZejh696Hy6vgZ0+fIZ/qt/0qZkFC2nVZaq0718saj51dYziZ6GEopX/ai24SsAAAA X-Change-ID: 20260310-fix-llvm-docs-1f91c1ec7608 To: Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Nicolas Schier , Jonathan Corbet , Shuah Khan , Alex Shi , Yanteng Si , Dongliang Mu Cc: llvm@lists.linux.dev, linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Gomez X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=3535; i=da.gomez@samsung.com; h=from:subject:message-id; bh=Now83fr/MP7zB3NxSTXc4S7AUV8dbchz0FScPQXarn0=; b=owEBbQKS/ZANAwAIAUCeo8QfGVH7AcsmYgBpsAWT735KRs6Ynl7QBvP+l2vLFq3J5JuTxcXUy A5xoqSH41WJAjMEAAEIAB0WIQTvdRrhHw9z4bnGPFNAnqPEHxlR+wUCabAFkwAKCRBAnqPEHxlR +9+ED/4i4lJ6+bbDZGtO4O7U1SGpSWb7KZ3yxnGtDIGVlb9G+vGzAyBqV85h5fuZnqGbw+Snpjj UR8xrvEP+oAFeSjfvNr9F/cjzgQAgxPiH+yPCrTHX70yaETTmiwB8BEochZK8rI0Xagt+v2qBop Q3uy4YvHTLgbib9F32xJ9U4Y6/EI9IVhF6MVyHGI8uj8sRXEHtYKI7k/GOIwqfK3nWnu3VYeMEJ +o40KvvD0ynm7SDeqeM7UCigjda8/xKsFO+MnPnWVlHIyZSk2k7zgtpb8RQxQucuXReoSi0ep3F zTGwbMhNaXeLeUZZwDicnsMpVeTijLRKHf8wT/lehtEfzwhJbazAKmPE6YHKMGXk/GIT2OH7BI6 2Dxmqmg00Kt4aTSdBO3drU6+1aQYVrWJcdgNeJVpHfWn7vhEdkpuoTUZ8oNgDyh4L6zwv3GVD8r PfYenoD3Lf6YW3S+L7jW/nPQjlq3CS0vYY8LKGgRbk496BzwU7GVWIStb31Q9eVnSonpGcBjXVT IgY8EK03Lawycw1fUzN7PEgnRrhYaV/gRMRlh1nXnei8PP00RGfyC1BrfHtvw/s5Fb1BkPmJC04 cr7io4N7nGqGDMN4JcLvpWCQxI3drMVoHVhqsiMiVOQi9nEEyq1HCRIdNV/NMLUgAnK8IFm9gFX 2HJwx7pu7zbOrkg== X-Developer-Key: i=da.gomez@samsung.com; a=openpgp; fpr=B2A7A9CFDD03B540FF58B27185F56EA4E9E8138F From: Daniel Gomez The ccache example in llvm.rst uses KBUILD_BUILD_TIMESTAMP=3D'' but the text says "should be set to a deterministic value". An empty string is not deterministic because init/Makefile uses $(or) which treats empty as false and falls through to $(shell LC_ALL=3DC date), embedding the current time: cat /tmp/test-or.mk build-timestamp-auto =3D fallback build-timestamp =3D $(or $(KBUILD_BUILD_TIMESTAMP),$(build-timestamp-auto)) all: @echo "[$(build-timestamp)]" make --file=3D/tmp/test-or.mk [fallback] KBUILD_BUILD_TIMESTAMP=3D'' make --file=3D/tmp/test-or.mk [fallback] KBUILD_BUILD_TIMESTAMP=3D"Sun Aug 25 20:57:08 UTC 1991" \ make --file=3D/tmp/test-or.mk [Sun Aug 25 20:57:08 UTC 1991] The same applies to a real kernel build: make O=3D../build LLVM=3D1 CC=3D"ccache clang" tinyconfig make O=3D../build LLVM=3D1 CC=3D"ccache clang" \ KBUILD_BUILD_TIMESTAMP=3D'' --jobs=3D$(nproc) cat ../build/include/generated/utsversion.h #define UTS_VERSION "#2 Wed Mar 4 12:13:43 CET 2026" Replace the empty string with an actual date, matching the pattern in kbuild.rst and reproducible-builds.rst. Use the first public Linux announcement as example date. make O=3D../build LLVM=3D1 CC=3D"ccache clang" tinyconfig make O=3D../build LLVM=3D1 CC=3D"ccache clang" \ KBUILD_BUILD_TIMESTAMP=3D"Sun Aug 25 20:57:08 UTC 1991" \ --jobs=3D$(nproc) cat ../build/include/generated/utsversion.h #define UTS_VERSION "#4 Sun Aug 25 20:57:08 UTC 1991" Signed-off-by: Daniel Gomez --- Do not use an empty KBUILD_BUILD_TIMESTAMP Makefile variable. --- Changes in v2: - EDITME: describe what is new in this series revision. - EDITME: use bulletpoints and terse descriptions. - Link to v1: https://lore.kernel.org/r/20260310-fix-llvm-docs-v1-1-2348788= 74762@samsung.com --- Documentation/kbuild/llvm.rst | 2 +- Documentation/translations/zh_CN/kbuild/llvm.rst | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst index bc8a283bc44b..ef46533d785f 100644 --- a/Documentation/kbuild/llvm.rst +++ b/Documentation/kbuild/llvm.rst @@ -128,7 +128,7 @@ Ccache KBUILD_BUILD_TIMESTAMP_ should be set to a deterministic value between bui= lds in order to avoid 100% cache misses, see Reproducible_builds_ for more inf= o):: =20 - KBUILD_BUILD_TIMESTAMP=3D'' make LLVM=3D1 CC=3D"ccache clang" + KBUILD_BUILD_TIMESTAMP=3D"Sun Aug 25 20:57:08 UTC 1991" make LLVM=3D1 CC= =3D"ccache clang" =20 .. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp .. _Reproducible_builds: reproducible-builds.html#timestamps diff --git a/Documentation/translations/zh_CN/kbuild/llvm.rst b/Documentati= on/translations/zh_CN/kbuild/llvm.rst index f87e0181d8e7..c68fd395f64c 100644 --- a/Documentation/translations/zh_CN/kbuild/llvm.rst +++ b/Documentation/translations/zh_CN/kbuild/llvm.rst @@ -116,7 +116,7 @@ Ccache KBUILD_BUILD_TIMESTAMP_ =E5=BA=94=E8=AE=BE=E7=BD=AE=E4=B8=BA=E5=90=8C=E4= =B8=80=E7=A1=AE=E5=AE=9A=E5=80=BC=EF=BC=8C=E4=BB=A5=E9=81=BF=E5=85=8D 100% = =E7=9A=84=E7=BC=93=E5=AD=98=E6=9C=AA=E5=91=BD=E4=B8=AD=EF=BC=8C =E8=AF=A6=E8=A7=81 Reproducible_builds_ =E8=8E=B7=E5=8F=96=E6=9B=B4=E5=A4= =9A=E4=BF=A1=E6=81=AF=EF=BC=89:: =20 - KBUILD_BUILD_TIMESTAMP=3D'' make LLVM=3D1 CC=3D"ccache clang" + KBUILD_BUILD_TIMESTAMP=3D"Sun Aug 25 20:57:08 UTC 1991" make LLVM=3D1 CC= =3D"ccache clang" =20 .. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp .. _Reproducible_builds: reproducible-builds.html#timestamps --- base-commit: 11439c4635edd669ae435eec308f4ab8a0804808 change-id: 20260310-fix-llvm-docs-1f91c1ec7608 Best regards, -- =20 Daniel Gomez