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bh=HZnBOeFGVZQcm4BscBgc1OFT4EXInuKSpyT4vCMq6Hk=; b=cQzbYHLRyVJpZUc7HgX2jfghcHo6y4RglJZGI8qjgtz6Da+inypuCg5XNDab++I0pzakh5 Q7jTVeA+S1gG+VrCESCKwt2l4L0/vmlB/uKty/sNBEssR7CCYuHnj/XY5Z1TjWjQztfr5F 5eVBTt/GQssH0rltz+VMGiPZy9mMXV0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1773690484; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=HZnBOeFGVZQcm4BscBgc1OFT4EXInuKSpyT4vCMq6Hk=; b=6A/x/RbjFU8+yM1Ph5aMLz7LP0AWvVXvw+q9rAO5d9TIZZFwEM5lfLVjaEhu3AwRITW3+o V38P0sGonnCk5PBA== From: Fabiano Rosas To: qemu-devel@nongnu.org Cc: Peter Xu , Zhao Liu , Paolo Bonzini , Roman Kiryanov , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Peter Maydell Subject: [PATCH v1] migration/savevm: Allow stub VMSDs Date: Mon, 16 Mar 2026 16:47:59 -0300 Message-ID: <20260316194759.22672-1-farosas@suse.de> X-Mailer: git-send-email 2.51.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Spamd-Result: default: False [-2.80 / 50.00]; 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charset="utf-8" After the referenced commit, empty VMStateDescription objects declared as part of stubs have started reaching the vmstate code. A valid VMStateDescription must at minimum have a name and either the .fields or .unmigratable fields set. Stubs, being empty, have none. Code that assumes a non-NULL name field will now cause a crash. E.g. $ ./build/mips/qemu-system-mipsel -nographic -drive if=3Dnone,format=3Dqcow= 2,file=3Ddummy.qcow2 [Type "C-a c" to get the "(qemu)" monitor prompt)] (qemu) savevm foo Backtrace from doing this under gdb: #0 0x0000555555df7d4d in vmsd_can_compress (field=3D0x5555564f78a0 <__compound_literal.3>) at ../../migration/vmstate.c:339 #1 0x0000555555df7dbb in vmsd_desc_field_start (vmsd=3D0x555556431ba0 , vmdesc=3D0x55555691= 8690, field=3D0x5555564f78a0 <__compound_literal.3>, i=3D0, max=3D1) at ../../migration/vmstate.c:362 #2 0x0000555555df85a7 in vmstate_save_state_v (f=3D0x555556b5a0c0, vmsd=3D0x555556431ba0 , opaque=3D0x555556c9aac0, vmdesc=3D0x555556918690, version_id=3D1, errp=3D0x7fffffffc948) at ../../migration/vmstate.c:528 #3 0x0000555555df8032 in vmstate_save_state (f=3D0x555556b5a0c0, vmsd=3D0x555556431ba0 , opaque=3D0x555556c9aac0, vmdesc_id=3D0x555556918690, errp=3D0x7ffffff= fc948) at ../../migration/vmstate.c:427 #4 0x0000555555df8f83 in vmstate_subsection_save (f=3D0x555556b5a0c0, vmsd=3D0x555556431c40 , opaque=3D0x555556c9aac0, vmdesc=3D0x555556918690, errp=3D0x7fffffffc9= 48) at ../../migration/vmstate.c:695 Due to their very nature, it's better to allow stubs to be completely empty instead of forcing any rules. Teach the code to skip them. Fixes: 7aa563630b ("pc: Start with modern CPU hotplug interface by default") Reported-by: Peter Maydell Signed-off-by: Fabiano Rosas --- migration/savevm.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/migration/savevm.c b/migration/savevm.c index dd58f2a705..e8d3360877 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -861,6 +861,10 @@ static void vmstate_check(const VMStateDescription *vm= sd) const VMStateField *field =3D vmsd->fields; const VMStateDescription * const *subsection =3D vmsd->subsections; =20 + if (!vmsd->name) { + return; + } + if (field) { while (field->name) { if (field->flags & (VMS_STRUCT | VMS_VSTRUCT)) { @@ -897,6 +901,11 @@ int vmstate_register_with_alias_id(VMStateIf *obj, uin= t32_t instance_id, { SaveStateEntry *se; =20 + if (!vmsd->name) { + /* assume it's a stub and ignore */ + return 0; + } + /* If this triggers, alias support can be dropped for the vmsd. */ assert(alias_id =3D=3D -1 || required_for_version >=3D vmsd->minimum_v= ersion_id); =20 --=20 2.51.0