[PATCH v4 01/19] liveupdate, kho: Remove __packed from KHO, LUO and memfd ABI structures
From: Tarun Sahu
Date: Tue Nov 10 2026 - 00:06:51 EST
All structures in include/linux/kho/abi/block.h (struct
kho_block_header_ser), include/linux/kho/abi/luo.h (struct luo_ser,
struct luo_file_ser, struct luo_file_set_ser, struct luo_session_ser,
struct luo_flb_header_ser, struct luo_flb_ser) and
include/linux/kho/abi/memfd.h (struct memfd_luo_folio_ser, struct
memfd_luo_ser) have naturally aligned fields on 64-bit architectures,
with no padding holes between fields or tail padding. Assert both the
structure size and 8-byte alignment under CONFIG_64BIT at compile time.
Any future unaligned field addition should come with reserved field to
keep the structure aligned.
Signed-off-by: Tarun Sahu <tarunsahu@xxxxxxxxxx>
---
include/linux/kho/abi/block.h | 10 +++++++--
include/linux/kho/abi/luo.h | 38 +++++++++++++++++++++++++++++------
include/linux/kho/abi/memfd.h | 16 ++++++++++++---
3 files changed, 53 insertions(+), 11 deletions(-)
diff --git a/include/linux/kho/abi/block.h b/include/linux/kho/abi/block.h
index d06d64b963be..36bdbaf9b3b8 100644
--- a/include/linux/kho/abi/block.h
+++ b/include/linux/kho/abi/block.h
@@ -12,7 +12,7 @@
* pre-update kernel to a post-update kernel.
*
* This interface is a contract. Any modification to the structure fields,
- * compatible strings, or the layout of the `__packed` serialization
+ * compatible strings, or the layout of the serialization
* structures defined here constitutes a breaking change. Such changes require
* incrementing the version number in the `KHO_FDT_COMPATIBLE` string to
* prevent a new kernel from misinterpreting data from an old kernel.
@@ -26,6 +26,8 @@
#define _LINUX_KHO_ABI_BLOCK_H
#include <asm/page.h>
+#include <linux/build_bug.h>
+#include <linux/kconfig.h>
#include <linux/types.h>
/**
@@ -49,6 +51,10 @@
struct kho_block_header_ser {
u64 next;
u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct kho_block_header_ser) == 16);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct kho_block_header_ser) == 8);
#endif /* _LINUX_KHO_ABI_BLOCK_H */
diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 288076de6d4a..721949374fa1 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -58,6 +58,8 @@
#define _LINUX_KHO_ABI_LUO_H
#include <linux/align.h>
+#include <linux/build_bug.h>
+#include <linux/kconfig.h>
#include <linux/kho/abi/block.h>
#include <uapi/linux/liveupdate.h>
@@ -82,7 +84,11 @@ struct luo_ser {
u64 liveupdate_num;
u64 sessions_pa;
u64 flbs_pa;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_ser) == 32);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_ser) == 8);
#define LIVEUPDATE_HNDL_COMPAT_LENGTH 48
@@ -98,7 +104,11 @@ struct luo_file_ser {
char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
u64 data;
u64 token;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_file_ser) == 64);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_file_ser) == 8);
/**
* struct luo_file_set_ser - Represents the serialized metadata for file set
@@ -113,7 +123,11 @@ struct luo_file_ser {
struct luo_file_set_ser {
u64 files;
u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_file_set_ser) == 16);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_file_set_ser) == 8);
/**
* struct luo_session_ser - Represents the serialized metadata for a LUO session.
@@ -131,7 +145,11 @@ struct luo_file_set_ser {
struct luo_session_ser {
char name[LIVEUPDATE_SESSION_NAME_LENGTH];
struct luo_file_set_ser file_set_ser;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_session_ser) == 80);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_session_ser) == 8);
/* The max size is set so it can be reliably used during in serialization */
#define LIVEUPDATE_FLB_COMPAT_LENGTH 48
@@ -152,7 +170,11 @@ struct luo_session_ser {
struct luo_flb_header_ser {
u64 pgcnt;
u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_flb_header_ser) == 16);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_flb_header_ser) == 8);
/**
* struct luo_flb_ser - Represents the serialized state of a single FLB object.
@@ -175,7 +197,11 @@ struct luo_flb_ser {
char name[LIVEUPDATE_FLB_COMPAT_LENGTH];
u64 data;
u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_flb_ser) == 64);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct luo_flb_ser) == 8);
/* Kernel Live Update Test ABI */
#ifdef CONFIG_LIVEUPDATE_TEST
diff --git a/include/linux/kho/abi/memfd.h b/include/linux/kho/abi/memfd.h
index 08b10fea2afc..376a724a1d8c 100644
--- a/include/linux/kho/abi/memfd.h
+++ b/include/linux/kho/abi/memfd.h
@@ -11,6 +11,8 @@
#ifndef _LINUX_KHO_ABI_MEMFD_H
#define _LINUX_KHO_ABI_MEMFD_H
+#include <linux/build_bug.h>
+#include <linux/kconfig.h>
#include <linux/types.h>
#include <linux/kho/abi/kexec_handover.h>
@@ -20,7 +22,7 @@
* memfd uses the ABI defined below for preserving its state across a kexec
* reboot using the LUO.
*
- * The state is serialized into a packed structure `struct memfd_luo_ser`
+ * The state is serialized into `struct memfd_luo_ser`
* which is handed over to the next kernel via the KHO mechanism.
*
* This interface is a contract. Any modification to the structure layout
@@ -54,7 +56,11 @@ struct memfd_luo_folio_ser {
u64 pfn:52;
u64 flags:12;
u64 index;
-} __packed;
+};
+
+static_assert(sizeof(struct memfd_luo_folio_ser) == 16);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct memfd_luo_folio_ser) == 8);
/*
* The set of seals this version supports preserving. If support for any new
@@ -85,7 +91,11 @@ struct memfd_luo_ser {
u32 flags;
u64 nr_folios;
struct kho_vmalloc folios;
-} __packed;
+};
+
+static_assert(sizeof(struct memfd_luo_ser) == 48);
+static_assert(!IS_ENABLED(CONFIG_64BIT) ||
+ __alignof__(struct memfd_luo_ser) == 8);
/* The compatibility string for memfd file handler */
#define MEMFD_LUO_FH_COMPATIBLE "memfd-v2"
--
2.56.0.506.g506a7eabc5-goog