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

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Date:   Tue, 16 Jul 2019 10:30:14 +0000
From:   Petr Tesarik <PTesarik@...e.com>
To:     Vasily Gorbik <gor@...ux.ibm.com>
CC:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philipp Rudo <prudo@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Laura Abbott" <labbott@...hat.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Raymund Will <rw@...e.com>
Subject: Re: [PATCH] s390: enable detection of kernel version from bzImage

On Tue, 16 Jul 2019 00:12:19 +0200
Vasily Gorbik <gor@...ux.ibm.com> wrote:

> 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@...ux.ibm.com>

This looks great! Much cleaner than the original approach.

Thank you,
Petr T

> ---
>  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 */
>  };
>