[PATCH v2 0/4] kexec: add kexec flag to control debug printing

[PATCH v2 0/4] kexec: add kexec flag to control debug printing

[Qiang Ma]

Overview:
=========
The commit cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control
debug printing") added the kexec_file flag to control debug printing.
However, for arm64, after commit 6f8c1da071a4 ("kexec_file, arm64: print
out debugging message if required"), when using the kexec_load interface,
the kexec_image_info function is called to print debug message, but
it uses kexec_dprintk, which is only available under kexec_file,
then when specifying 'kexec -d', kexec_load interface will print nothing.

For riscv, commit eb7622d908a09 ("kexec_file, riscv: print out debugging
message if required") remove kexec_image_info(), because the content has
been printed out in generic code in kexec_file_load, but not in kexec_load.

Therefore, in order to solve the two problems mentioned above, for this
patchset, several things need to be done:

1. Enabling kexec_dprintk is available for kexec_load.
2. Add some debugging message of the deleted kexec_image_info
   to generic code.
3. Remove duplicate debugging prints for arm64.

Since kexec_load and kexec_file_load are not triggered simultaneously,
we can unify the debug flag of kexec and kexec_file as kexec_dbg_print.

In this way, kexec_dprintk is available for kexec_load and kexec_file_load.

Then when specifying 'kexec -d', the debugging message using kexec_dprintk
in kexec_image_info can be printed normally.

The following are the key points of the specific changes:

1. rename kexec_file_dbg_print to kexec_dbg_print
2. Add KEXEC_DEBUG
3. Initialize kexec_dbg_print for kexec
4. Set the reset of kexec_dbg_print to kimage_free

Testing:
=========
I did testing on x86_64, arm64 and loongarch. On x86_64, the printed
messages look like below:

Unset CONFIG_KEXEC_FILE:
[   36.774228] kexec_file: kernel: 0000000066c386c8 kernel_size: 0xd78400
[   36.821814] kexec-bzImage64: Loaded purgatory at 0x23fffb000
[   36.821826] kexec-bzImage64: Loaded boot_param, command line and misc at 0x23fff9000 bufsz=0x12d0 memsz=0x2000
[   36.821829] kexec-bzImage64: Loaded 64bit kernel at 0x23d400000 bufsz=0xd73400 memsz=0x2ab7000
[   36.821918] kexec-bzImage64: Loaded initrd at 0x23bd0b000 bufsz=0x16f40a8 memsz=0x16f40a8
[   36.821920] kexec-bzImage64: Final command line is: root=/dev/mapper/test-root crashkernel=auto rd.lvm.lv=test/root
[   36.821925] kexec-bzImage64: E820 memmap:
[   36.821926] kexec-bzImage64: 0000000000000000-000000000009ffff (1)
[   36.821928] kexec-bzImage64: 0000000000100000-0000000000811fff (1)
[   36.821930] kexec-bzImage64: 0000000000812000-0000000000812fff (2)
[   36.821931] kexec-bzImage64: 0000000000813000-00000000bee38fff (1)
[   36.821933] kexec-bzImage64: 00000000bee39000-00000000beec2fff (2)
[   36.821934] kexec-bzImage64: 00000000beec3000-00000000bf8ecfff (1)
[   36.821935] kexec-bzImage64: 00000000bf8ed000-00000000bfb6cfff (2)
[   36.821936] kexec-bzImage64: 00000000bfb6d000-00000000bfb7efff (3)
[   36.821937] kexec-bzImage64: 00000000bfb7f000-00000000bfbfefff (4)
[   36.821938] kexec-bzImage64: 00000000bfbff000-00000000bff7bfff (1)
[   36.821939] kexec-bzImage64: 00000000bff7c000-00000000bfffffff (2)
[   36.821940] kexec-bzImage64: 00000000feffc000-00000000feffffff (2)
[   36.821941] kexec-bzImage64: 00000000ffc00000-00000000ffffffff (2)
[   36.821942] kexec-bzImage64: 0000000100000000-000000023fffffff (1)
[   36.872348] kexec_file: nr_segments = 4
[   36.872356] kexec_file: segment[0]: buf=0x000000005314ece7 bufsz=0x4000 mem=0x23fffb000 memsz=0x5000
[   36.872370] kexec_file: segment[1]: buf=0x000000006e59b143 bufsz=0x12d0 mem=0x23fff9000 memsz=0x2000
[   36.872374] kexec_file: segment[2]: buf=0x00000000eb7b1fc3 bufsz=0xd73400 mem=0x23d400000 memsz=0x2ab7000
[   36.882172] kexec_file: segment[3]: buf=0x000000006af76441 bufsz=0x16f40a8 mem=0x23bd0b000 memsz=0x16f5000
[   36.889113] kexec_file: kexec_file_load: type:0, start:0x23fffb150 head:0x101a2e002 flags:0x8

On aarch64, the printed messages look like below:

Set CONFIG_KEXEC_FILE
[   39.033203] kexec_file: kernel: 0000000073414684 kernel_size: 0x3123a00
[   39.047010] kexec_file: Loaded initrd at 0x43cf0000 bufsz=0x17e0e19 memsz=0x17e1000
[   39.047054] kexec_file: Loaded dtb at 0x23ec00000 bufsz=0x386 memsz=0x1000
[   39.047056] kexec_file(Image): Loaded kernel at 0x40000000 bufsz=0x3123a00 memsz=0x3cf0000
[   39.047063] kexec_file: nr_segments = 3
[   39.047064] kexec_file: segment[0]: buf=0x0000000073414684 bufsz=0x3123a00 mem=0x40000000 memsz=0x3cf0000
[   39.073612] kexec_file: segment[1]: buf=0x000000005cd5746b bufsz=0x17e0e19 mem=0x43cf0000 memsz=0x17e1000
[   39.085309] kexec_file: segment[2]: buf=0x0000000084c4a0f1 bufsz=0x386 mem=0x23ec00000 memsz=0x1000
[   39.085459] machine_kexec_post_load:155:
[   39.085463]   kexec kimage info:
[   39.085467]     kern_reloc: 0x00000001620e2000
[   39.085468]     el2_vectors: 0x0000000000000000
[   39.085470] kexec_file: kexec_file_load: type:0, start:0x40000000 head:0x1620e4002 flags:0x8

Unset CONFIG_KEXEC_FILE:

With this patch:
[   35.156088] machine_kexec_post_load:155:
[   35.156097]   kexec kimage info:
[   35.156101]     kern_reloc: 0x000000011c134000
[   35.156102]     el2_vectors: 0x0000000000000000
[   35.156104] kexec: kexec_load: type:0, start:0x454d26b0 head:0x105c14002 flags:0xb70010

Without this patch:
There is no kexec print in dmesg.

Previous posts:
Link: https://lore.kernel.org/all/aTdxEvqY6Bcy7Wa1@MiWiFi-R3L-srv/

Changes in v2:
==========
- Remove the Reported-by record of patch "kexec: print out debugging
  message if required for kexec_load"
- Move patch "kexec: Replace the goto out_unlock with out" to this patchset

Qiang Ma (4):
  kexec: Replace the goto out_unlock with out
  kexec: add kexec flag to control debug printing
  kexec: print out debugging message if required for kexec_load
  arm64: kexec: Adjust the debug print of kexec_image_info

 arch/arm64/kernel/machine_kexec.c | 2 --
 include/linux/kexec.h             | 9 +++++----
 include/uapi/linux/kexec.h        | 1 +
 kernel/kexec.c                    | 8 +++++++-
 kernel/kexec_core.c               | 4 +++-
 kernel/kexec_file.c               | 4 +---
 6 files changed, 17 insertions(+), 11 deletions(-)

-- 
2.20.1

[PATCH v2 1/4] kexec: Replace the goto out_unlock with out

[Qiang Ma]

The image is initialized to NULL. Then, after calling kimage_alloc_init,
we can directly goto 'out' because at this time, the kimage_free will
determine whether image is a NULL pointer.

This will prepare for the subsequent patch to reset the variable in
kimage_free.

Signed-off-by: Qiang Ma <maqianga@uniontech.com>
---
 kernel/kexec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 28008e3d462e..9bb1f2b6b268 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -95,6 +95,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 	unsigned long i;
 	int ret;
 
+	image = NULL;
+
 	/*
 	 * Because we write directly to the reserved memory region when loading
 	 * crash kernels we need a serialization here to prevent multiple crash
@@ -129,7 +131,7 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 
 	ret = kimage_alloc_init(&image, entry, nr_segments, segments, flags);
 	if (ret)
-		goto out_unlock;
+		goto out;
 
 	if (flags & KEXEC_PRESERVE_CONTEXT)
 		image->preserve_context = 1;
-- 
2.20.1

[PATCH v2 2/4] kexec: add kexec flag to control debug printing

[Qiang Ma]

The commit cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control
debug printing") added the kexec_file flag to control debug printing.
However, for arm64, after commit 6f8c1da071a4 ("kexec_file, arm64: print
out debugging message if required"), when using the kexec_load interface,
the kexec_image_info function is called to print debug message, but
it uses kexec_dprintk, which is only available under kexec_file,
then when specifying 'kexec -d', kexec_load interface will print nothing.

For riscv, commit eb7622d908a09 ("kexec_file, riscv: print out debugging
message if required") remove kexec_image_info(), because the content has
been printed out in generic code in kexec_file_load, but not in kexec_load.

Therefore, in order to solve the two problems mentioned above, for this
patchset, several things need to be done:

1. Enabling kexec_dprintk is available for kexec_load.
2. Add some debugging message of the deleted kexec_image_info
   to generic code.
3. Remove duplicate debugging prints for arm64

Since kexec_load and kexec_file_load are not triggered simultaneously,
we can unify the debug flag of kexec and kexec_file as kexec_dbg_print.

In this way, kexec_dprintk is available for kexec_load and kexec_file_load.

The following are the key points of the specific changes:

1. rename kexec_file_dbg_print to kexec_dbg_print
2. Add KEXEC_DEBUG
3. Initialize kexec_dbg_print for kexec
4. Set the reset of kexec_dbg_print to kimage_free

Signed-off-by: Qiang Ma <maqianga@uniontech.com>
---
 include/linux/kexec.h      | 9 +++++----
 include/uapi/linux/kexec.h | 1 +
 kernel/kexec.c             | 1 +
 kernel/kexec_core.c        | 4 +++-
 kernel/kexec_file.c        | 4 +---
 5 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index ff7e231b0485..23f10aec0b34 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -455,10 +455,11 @@ bool kexec_load_permitted(int kexec_image_type);
 
 /* List of defined/legal kexec flags */
 #ifndef CONFIG_KEXEC_JUMP
-#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR | KEXEC_CRASH_HOTPLUG_SUPPORT)
+#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR | KEXEC_CRASH_HOTPLUG_SUPPORT | \
+			KEXEC_DEBUG)
 #else
 #define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR | \
-			KEXEC_CRASH_HOTPLUG_SUPPORT)
+			KEXEC_CRASH_HOTPLUG_SUPPORT | KEXEC_DEBUG)
 #endif
 
 /* List of defined/legal kexec file flags */
@@ -525,10 +526,10 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
 static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
 #endif
 
-extern bool kexec_file_dbg_print;
+extern bool kexec_dbg_print;
 
 #define kexec_dprintk(fmt, arg...) \
-        do { if (kexec_file_dbg_print) pr_info(fmt, ##arg); } while (0)
+	do { if (kexec_dbg_print) pr_info(fmt, ##arg); } while (0)
 
 extern void *kimage_map_segment(struct kimage *image, unsigned long addr, unsigned long size);
 extern void kimage_unmap_segment(void *buffer);
diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
index 55749cb0b81d..819c600af125 100644
--- a/include/uapi/linux/kexec.h
+++ b/include/uapi/linux/kexec.h
@@ -14,6 +14,7 @@
 #define KEXEC_PRESERVE_CONTEXT	0x00000002
 #define KEXEC_UPDATE_ELFCOREHDR	0x00000004
 #define KEXEC_CRASH_HOTPLUG_SUPPORT 0x00000008
+#define KEXEC_DEBUG		0x00000010
 #define KEXEC_ARCH_MASK		0xffff0000
 
 /*
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 9bb1f2b6b268..f6c58c767eb0 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -42,6 +42,7 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
 	if (!image)
 		return -ENOMEM;
 
+	kexec_dbg_print = !!(flags & KEXEC_DEBUG);
 	image->start = entry;
 	image->nr_segments = nr_segments;
 	memcpy(image->segment, segments, nr_segments * sizeof(*segments));
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 0f92acdd354d..d7c2a2b79214 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -55,7 +55,7 @@ atomic_t __kexec_lock = ATOMIC_INIT(0);
 /* Flag to indicate we are going to kexec a new kernel */
 bool kexec_in_progress = false;
 
-bool kexec_file_dbg_print;
+bool kexec_dbg_print;
 
 /*
  * When kexec transitions to the new kernel there is a one-to-one
@@ -578,6 +578,8 @@ void kimage_free(struct kimage *image)
 	kimage_entry_t *ptr, entry;
 	kimage_entry_t ind = 0;
 
+	kexec_dbg_print = false;
+
 	if (!image)
 		return;
 
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index eb62a9794242..3f1d6c4e8ff2 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -138,8 +138,6 @@ void kimage_file_post_load_cleanup(struct kimage *image)
 	 */
 	kfree(image->image_loader_data);
 	image->image_loader_data = NULL;
-
-	kexec_file_dbg_print = false;
 }
 
 #ifdef CONFIG_KEXEC_SIG
@@ -314,7 +312,7 @@ kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
 	if (!image)
 		return -ENOMEM;
 
-	kexec_file_dbg_print = !!(flags & KEXEC_FILE_DEBUG);
+	kexec_dbg_print = !!(flags & KEXEC_FILE_DEBUG);
 	image->file_mode = 1;
 
 #ifdef CONFIG_CRASH_DUMP
-- 
2.20.1

[PATCH v2 3/4] kexec: print out debugging message if required for kexec_load

[Qiang Ma]

The commit a85ee18c7900 ("kexec_file: print out debugging message
if required") has added general code printing in kexec_file_load(),
but not in kexec_load().

As a result, when using '-d' for the kexec_load interface,
print nothing in the kernel space.

Since the segments debugging message has already been printed by the
user-space tool kexec-tools, it will not be printed here in the
kernel space.

And print out type/start/head of kimage and flags to help debug.

Signed-off-by: Qiang Ma <maqianga@uniontech.com>
---
 kernel/kexec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index f6c58c767eb0..37e4ac8af9f3 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -166,6 +166,9 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 	if (ret)
 		goto out;
 
+	kexec_dprintk("kexec_load: type:%u, start:0x%lx head:0x%lx flags:0x%lx\n",
+		      image->type, image->start, image->head, flags);
+
 	/* Install the new kernel and uninstall the old */
 	image = xchg(dest_image, image);
 
-- 
2.20.1

[PATCH v2 4/4] arm64: kexec: Adjust the debug print of kexec_image_info

[Qiang Ma]

In the previous patch, we move start/head of kimage to the
generic code, so, we remove them to avoid duplicate printing.

Signed-off-by: Qiang Ma <maqianga@uniontech.com>
---
 arch/arm64/kernel/machine_kexec.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 239c16e3d02f..0896e3e6a811 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -34,8 +34,6 @@ static void _kexec_image_info(const char *func, int line,
 {
 	kexec_dprintk("%s:%d:\n", func, line);
 	kexec_dprintk("  kexec kimage info:\n");
-	kexec_dprintk("    type:        %d\n", kimage->type);
-	kexec_dprintk("    head:        %lx\n", kimage->head);
 	kexec_dprintk("    kern_reloc: %pa\n", &kimage->arch.kern_reloc);
 	kexec_dprintk("    el2_vectors: %pa\n", &kimage->arch.el2_vectors);
 }
-- 
2.20.1

Re: [PATCH v2 4/4] arm64: kexec: Adjust the debug print of kexec_image_info

[Will Deacon]

On Fri, Dec 19, 2025 at 05:31:34PM +0800, Qiang Ma wrote:
> In the previous patch, we move start/head of kimage to the
> generic code, so, we remove them to avoid duplicate printing.
> 
> Signed-off-by: Qiang Ma <maqianga@uniontech.com>
> ---
>  arch/arm64/kernel/machine_kexec.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index 239c16e3d02f..0896e3e6a811 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -34,8 +34,6 @@ static void _kexec_image_info(const char *func, int line,
>  {
>  	kexec_dprintk("%s:%d:\n", func, line);
>  	kexec_dprintk("  kexec kimage info:\n");
> -	kexec_dprintk("    type:        %d\n", kimage->type);
> -	kexec_dprintk("    head:        %lx\n", kimage->head);
>  	kexec_dprintk("    kern_reloc: %pa\n", &kimage->arch.kern_reloc);
>  	kexec_dprintk("    el2_vectors: %pa\n", &kimage->arch.el2_vectors);
>  }
> -- 
> 2.20.1

Acked-by: Will Deacon <will@kernel.org>

Will

Re: [PATCH v2 0/4] kexec: add kexec flag to control debug printing

[Andrew Morton]

On Fri, 19 Dec 2025 17:31:30 +0800 Qiang Ma <maqianga@uniontech.com> wrote:

> The commit cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control
> debug printing") added the kexec_file flag to control debug printing.
> However, for arm64, after commit 6f8c1da071a4 ("kexec_file, arm64: print
> out debugging message if required"), when using the kexec_load interface,
> the kexec_image_info function is called to print debug message, but
> it uses kexec_dprintk, which is only available under kexec_file,
> then when specifying 'kexec -d', kexec_load interface will print nothing.
> 
> For riscv, commit eb7622d908a09 ("kexec_file, riscv: print out debugging
> message if required") remove kexec_image_info(), because the content has
> been printed out in generic code in kexec_file_load, but not in kexec_load.
> 
> Therefore, in order to solve the two problems mentioned above, for this
> patchset, several things need to be done:
> 
> 1. Enabling kexec_dprintk is available for kexec_load.
> 2. Add some debugging message of the deleted kexec_image_info
>    to generic code.
> 3. Remove duplicate debugging prints for arm64.

Some additional review input on this series would be good, if someone
has the time.

Re: [PATCH v2 0/4] kexec: add kexec flag to control debug printing

[Baoquan He]

On 01/19/26 at 03:49pm, Andrew Morton wrote:
> On Fri, 19 Dec 2025 17:31:30 +0800 Qiang Ma <maqianga@uniontech.com> wrote:
> 
> > The commit cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control
> > debug printing") added the kexec_file flag to control debug printing.
> > However, for arm64, after commit 6f8c1da071a4 ("kexec_file, arm64: print
> > out debugging message if required"), when using the kexec_load interface,
> > the kexec_image_info function is called to print debug message, but
> > it uses kexec_dprintk, which is only available under kexec_file,
> > then when specifying 'kexec -d', kexec_load interface will print nothing.
> > 
> > For riscv, commit eb7622d908a09 ("kexec_file, riscv: print out debugging
> > message if required") remove kexec_image_info(), because the content has
> > been printed out in generic code in kexec_file_load, but not in kexec_load.
> > 
> > Therefore, in order to solve the two problems mentioned above, for this
> > patchset, several things need to be done:
> > 
> > 1. Enabling kexec_dprintk is available for kexec_load.
> > 2. Add some debugging message of the deleted kexec_image_info
> >    to generic code.
> > 3. Remove duplicate debugging prints for arm64.
> 
> Some additional review input on this series would be good, if someone
> has the time.

As I have said before, I am not fan of this patchset becuase I think
it's not necessary, even though it has no much harm except of adding code.
Leave this to those who like it.