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pr=C Message-ID: Date: Thu, 8 Oct 2026 13:57:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] xen/device-tree: add a helper to dump an FDT in DTS-like format To: Oleksii Kurochko , CC: Andrew Cooper , Anthony PERARD , Jan Beulich , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , Bertrand Marquis References: <20261001111630.112472-1-oleksii.kurochko@gmail.com> <20261001111630.112472-2-oleksii.kurochko@gmail.com> From: "Orzel, Michal" Content-Language: en-US In-Reply-To: <20261001111630.112472-2-oleksii.kurochko@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA2PEPF00003F62:EE_|SJ0PR12MB5612:EE_ X-MS-Office365-Filtering-Correlation-Id: 4911ef6f-4459-4f78-be77-08df25334c12 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|36860700016|82310400026|376014|1800799024|6133799003|11063799006|5023799004|56012099006|4143699003|10067099003|22082099003|18002099003|3023799007; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: pP1Oywsnu7GlM5JPUW+RhnzSIr8S2vlZCivVQ9UD/AAzzBN3KBl4PdZY2/RVL+iYOYFf1YqmtrLkzEi7KTqzHLY8ALJOb/835XhDbtGFjnZpMnZDa0f45vV0MUvGxjLMt8wpJKPxtx8msvQ6T1eWtPAHVAGeG9suJVDAMG/W9jVLy7arzLLbQWduSIk9nyk1E0Cyn2FGUaNdbjF0ylm/zQ+poa2sXgYIs7Zy8H1dgyHgke49eQ/2w4zVgkDNpt7zJG2IEuOwhICyq+FOKn7PmKdq1vLiRb2ddGYkL0NwYt679BD0inx8PItdT87n9QWR1W9rNOhE1IHKFPGrNvp2JVzawXat3vtRZe4E1ZZryGG3y5SWaoU1ZOSL7aUnNd+o5ooiBzB71gigDbuuTG81KdzcQ7XuUpBVNI2P5Y/2cY29rpiq/gS4gdxC1UjPjlEe X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Oct 2026 11:57:15.9133 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4911ef6f-4459-4f78-be77-08df25334c12 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SA2PEPF00003F62.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB5612 X-purgate-ID: tlsNG-33051d/1791460644-754844E9-031CB6EB/10/73395122804 X-purgate-type: spam X-purgate-size: 5531 On 01-Oct-26 13:16, Oleksii Kurochko wrote: > The device tree Xen builds for a dom0less domain is only ever consumed > by the guest, so a mistake in it surfaces as an obscure failure inside > the domain, far away from the code which produced the tree. > > Add device_tree_dump(). The output follows dtc's format so that a dump > can be diffed against the source DTS or fed back to dtc; the value > formatting heuristics are ported from dtc's utilfdt_print_data() for > that reason. The walk itself goes through libfdt rather than decoding > the tag stream by hand as dtc's fdtdump does. > > Dumping a whole tree is only useful while debugging and costs both code > size and a lot of console output, hence CONFIG_DEVICE_TREE_DEBUG. Mention > the dump in the help text of the option. We should also dump the DTB for dom0/hwdom in prepare_dtb_hwdom(). Please add that to this patch. > > Signed-off-by: Oleksii Kurochko > --- > xen/Kconfig.debug | 3 +- > xen/common/device-tree/Makefile | 1 + > xen/common/device-tree/dom0less-build.c | 4 + > xen/common/device-tree/fdt-dump.c | 180 ++++++++++++++++++++++++ > xen/include/xen/bootfdt.h | 13 ++ > 5 files changed, 200 insertions(+), 1 deletion(-) > create mode 100644 xen/common/device-tree/fdt-dump.c > > diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug > index d900d926c555..664f50bf8a96 100644 > --- a/xen/Kconfig.debug > +++ b/xen/Kconfig.debug > @@ -95,7 +95,8 @@ config DEVICE_TREE_DEBUG > depends on DEVICE_TREE_PARSE > help > Device tree parsing and DOM0 device tree building messages are > - logged in the Xen ring buffer. > + logged in the Xen ring buffer. The device tree generated for each > + dom0less domU is dumped there as well, in a DTS-like format. I think we could have a separate option DEVICE_TREE_DUMP that depends on DEVICE_TREE_PARSE. Sometimes all we need is just to see how the generated DTB look like without seeing thousands of other DT debug messages. Especially that nothing in fdt-dump.c depends on DEVICE_TREE_DEBUG. > If unsure, say N here. > > config SCRUB_DEBUG > diff --git a/xen/common/device-tree/Makefile b/xen/common/device-tree/Makefile > index 9036e455d66a..959dd2a9fd30 100644 > --- a/xen/common/device-tree/Makefile > +++ b/xen/common/device-tree/Makefile > @@ -6,6 +6,7 @@ obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += domain-build.init.o > obj-$(filter $(CONFIG_DOM0LESS_BOOT),$(CONFIG_HAS_DEVICE_TREE_DISCOVERY)) += dom0less-build.init.o > obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-bindings.init.o > obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o > +obj-$(CONFIG_DEVICE_TREE_DEBUG) += fdt-dump.init.o > obj-$(CONFIG_HAS_DEVICE_TREE_DISCOVERY) += intc.o > obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += kernel.o > obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o > diff --git a/xen/common/device-tree/dom0less-build.c b/xen/common/device-tree/dom0less-build.c > index fcbeb8adbd73..182201384faf 100644 > --- a/xen/common/device-tree/dom0less-build.c > +++ b/xen/common/device-tree/dom0less-build.c > @@ -1,5 +1,6 @@ > /* SPDX-License-Identifier: GPL-2.0-only */ > > +#include > #include > #include > #include > @@ -587,6 +588,9 @@ static int __init prepare_dtb_domU(struct domain *d, struct kernel_info *kinfo) > if ( ret < 0 ) > goto err; > > + dt_dprintk("Device tree for %pd:\n", d); Move this message to device_tree_dump. > + device_tree_dump(kinfo->fdt); > + > return 0; > > err: > diff --git a/xen/common/device-tree/fdt-dump.c b/xen/common/device-tree/fdt-dump.c > new file mode 100644 > index 000000000000..fc3d9eca5891 > --- /dev/null > +++ b/xen/common/device-tree/fdt-dump.c > @@ -0,0 +1,180 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +/* > + * Dump a flattened device tree blob in a DTS-like format. > + * > + * is_printable_string() and print_value() are derived from > + * util_is_printable_string() and utilfdt_print_data() in the device tree > + * compiler (dtc). > + * > + * Copyright 2011 The Chromium Authors, All Rights Reserved. > + * Copyright 2008 Jon Loeliger, Freescale Semiconductor, Inc. > + * util_is_printable_string contributed by > + * Pantelis Antoniou > + */ > + > +#include > +#include > +#include > +#include > +#include > +#include > + > +/* Deeper nodes are still printed, but not indented any further. */ > +#define DUMP_MAX_INDENT_DEPTH 32 > + > +/* Indentation, in characters, of a node at depth @depth. */ > +static int __init indent_of(int depth) > +{ > + return 2 * min(depth, DUMP_MAX_INDENT_DEPTH); > +} > + > +static bool __init is_printable_string(const void *data, unsigned int len) > +{ > + const char *s = data; > + const char *se = s + len; > + > + /* A zero length property, or one which isn't NUL terminated, isn't one. */ > + if ( (len == 0) || (s[len - 1] != '\0') ) > + return false; > + > + while ( s < se ) > + { > + const char *ss = s; > + > + while ( (s < se) && *s && isprint(*s) ) Xen's is_print() behaves differently than what dtc uses. You need to combine it with is_ascii. Otherwise 0xff would be marked as printable. ~Michal