[PATCH] s390: enable detection of kernel version from bzImage

[Vasily Gorbik]

Extend "parmarea" to include an offset of the version string, which is
stored as 8-byte big endian value.

To retrieve version string from bzImage reliably, one should check the
presence of "S390EP" ascii string at 0x10008 (available since v3.2),
then read the version string offset from 0x10428 (which has been 0
since v3.2 up to now). The string is null terminated.

Could be retrieved with the following "file" command magic (requires
file v5.34):
8 string \x02\x00\x00\x18\x60\x00\x00\x50\x02\x00\x00\x68\x60\x00\x00\x50\x40\x40\x40\x40\x40\x40\x40\x40 Linux S390
>0x10008       string          S390EP
>>0x10428      bequad          >0
>>>(0x10428.Q) string          >\0             \b, version %s

Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
---
 arch/s390/boot/Makefile       | 2 +-
 arch/s390/boot/head.S         | 1 +
 arch/s390/boot/version.c      | 6 ++++++
 arch/s390/include/asm/setup.h | 4 +++-
 4 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 arch/s390/boot/version.c

diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
index 7cba96e7587b..4cf0bddb7d92 100644
--- a/arch/s390/boot/Makefile
+++ b/arch/s390/boot/Makefile
@@ -36,7 +36,7 @@ CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char
 
 obj-y	:= head.o als.o startup.o mem_detect.o ipl_parm.o ipl_report.o
 obj-y	+= string.o ebcdic.o sclp_early_core.o mem.o ipl_vmparm.o cmdline.o
-obj-y	+= ctype.o text_dma.o
+obj-y	+= version.o ctype.o text_dma.o
 obj-$(CONFIG_PROTECTED_VIRTUALIZATION_GUEST)	+= uv.o
 obj-$(CONFIG_RELOCATABLE)	+= machine_kexec_reloc.o
 obj-$(CONFIG_RANDOMIZE_BASE)	+= kaslr.o
diff --git a/arch/s390/boot/head.S b/arch/s390/boot/head.S
index 028aab03a9e7..2087bed6e60f 100644
--- a/arch/s390/boot/head.S
+++ b/arch/s390/boot/head.S
@@ -361,6 +361,7 @@ ENTRY(startup_kdump)
 	.quad	0			# INITRD_SIZE
 	.quad	0			# OLDMEM_BASE
 	.quad	0			# OLDMEM_SIZE
+	.quad	kernel_version		# points to kernel version string
 
 	.org	COMMAND_LINE
 	.byte	"root=/dev/ram0 ro"
diff --git a/arch/s390/boot/version.c b/arch/s390/boot/version.c
new file mode 100644
index 000000000000..ea5e49651931
--- /dev/null
+++ b/arch/s390/boot/version.c
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <generated/utsrelease.h>
+#include <generated/compile.h>
+
+const char kernel_version[] = UTS_RELEASE
+	" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ") " UTS_VERSION;
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 925889d360c1..e5d28a475f76 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -54,6 +54,7 @@
 #define INITRD_SIZE_OFFSET	0x10410
 #define OLDMEM_BASE_OFFSET	0x10418
 #define OLDMEM_SIZE_OFFSET	0x10420
+#define KERNEL_VERSION_OFFSET	0x10428
 #define COMMAND_LINE_OFFSET	0x10480
 
 #ifndef __ASSEMBLY__
@@ -74,7 +75,8 @@ struct parmarea {
 	unsigned long initrd_size;			/* 0x10410 */
 	unsigned long oldmem_base;			/* 0x10418 */
 	unsigned long oldmem_size;			/* 0x10420 */
-	char pad1[0x10480 - 0x10428];			/* 0x10428 - 0x10480 */
+	unsigned long kernel_version;			/* 0x10428 */
+	char pad1[0x10480 - 0x10430];			/* 0x10430 - 0x10480 */
 	char command_line[ARCH_COMMAND_LINE_SIZE];	/* 0x10480 */
 };
 
-- 
2.21.0