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Date:   Mon, 25 Jun 2018 17:09:19 +0200
From:   Vasily Gorbik <gor@linux.ibm.com>
To:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc:     Heiko Carstens <heiko.carstens@de.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Guenter Roeck <linux@roeck-us.net>, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org, qemu-s390x <qemu-s390x@nongnu.org>,
        qemu-devel <qemu-devel@nongnu.org>,
        Thomas Huth <thuth@redhat.com>
Subject: [PATCH] s390/boot: block uncompressed vmlinux booting attempts
References: <64bcba64-b88f-3594-da6e-7c2118482c20@roeck-us.net>
 <cover.thread-8b0da3.your-ad-here.call-01529937119-ext-3705@work.hours>
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Sender: linux-kernel-owner@vger.kernel.org
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Since uncompressed kernel image "vmlinux" elf file is not bootable under
qemu anymore, add a check which would report that.

Qemu users are encouraged to use bzImage or
arch/s390/boot/compressed/vmlinux instead.

The check relies on s390 linux entry point ABI definition, which is only
present in bzImage and arch/s390/boot/compressed/vmlinux.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
 arch/s390/boot/head.S         |  4 ++--
 arch/s390/include/asm/setup.h |  3 ++-
 arch/s390/kernel/early.c      | 12 ++++++++++++
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/s390/boot/head.S b/arch/s390/boot/head.S
index f09e792df495..f721913b73f1 100644
--- a/arch/s390/boot/head.S
+++ b/arch/s390/boot/head.S
@@ -272,14 +272,14 @@ iplstart:
 	.org	0x10000
 ENTRY(startup)
 	j	.Lep_startup_normal
-	.org	0x10008
+	.org	EP_OFFSET
 #
 # This is a list of s390 kernel entry points. At address 0x1000f the number of
 # valid entry points is stored.
 #
 # IMPORTANT: Do not change this table, it is s390 kernel ABI!
 #
-	.ascii	"S390EP"
+	.ascii	EP_STRING
 	.byte	0x00,0x01
 #
 # kdump startup-code at 0x10010, running in 64 bit absolute addressing mode
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index be02f0558048..1d66016f4170 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -9,7 +9,8 @@
 #include <linux/const.h>
 #include <uapi/asm/setup.h>
 
-
+#define EP_OFFSET		0x10008
+#define EP_STRING		"S390EP"
 #define PARMAREA		0x10400
 #define PARMAREA_END		0x11000
 
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 827699eb48fa..45c5be3d8777 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -331,8 +331,20 @@ static void __init setup_boot_command_line(void)
 	append_to_cmdline(append_ipl_scpdata);
 }
 
+static void __init check_image_bootable(void)
+{
+	if (!memcmp(EP_STRING, (void *)EP_OFFSET, strlen(EP_STRING)))
+		return;
+
+	sclp_early_printk("The linux kernel boot failure: the image is corrupted or not bootable.\n");
+	sclp_early_printk("Please check that you are using bootable kernel image \"bzImage\".\n");
+	sclp_early_printk("(or alternatively \"arch/s390/boot/compressed/vmlinux\" image for qemu)\n");
+	disabled_wait(0xbadb007);
+}
+
 void __init startup_init(void)
 {
+	check_image_bootable();
 	time_early_init();
 	init_kernel_storage_key();
 	lockdep_off();
-- 
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