powerpc: Support for relocatable kdump kernel

This adds relocatable kernel support for kdump. With this one can
use the same regular kernel to capture the kdump. A signature (0xfeed1234)
is passed in r6 from panic code to the next kernel through kexec_sequence
and purgatory code. The signature is used to differentiate between
kdump kernel and non-kdump kernels.

The purgatory code compares the signature and sets the __kdump_flag in
head_64.S.  During the boot up, kernel code checks __kdump_flag and if it
is set, the kernel will behave as relocatable kdump kernel. This kernel
will boot at the address where it was loaded by kexec-tools ie. at the
address reserved through crashkernel boot parameter.

CONFIG_CRASH_DUMP depends on CONFIG_RELOCATABLE option to build kdump
kernel as relocatable. So the same kernel can be used as production and
kdump kernel.

This patch incorporates the changes suggested by Paul Mackerras to avoid
GOT use and to avoid two copies of the code.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Mohan Kumar M <mohan@in.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 12 insertions, 5 deletions

diff --git a/arch/powerpc/include/asm/kdump.h b/arch/powerpc/include/asm/kdump.h
index f6c93c716898..a503da9d56f3 100644
--- a/arch/powerpc/include/asm/kdump.h
+++ b/arch/powerpc/include/asm/kdump.h
@@ -9,6 +9,12 @@
  * Reserve to the end of the FWNMI area, see head_64.S */
 #define KDUMP_RESERVE_LIMIT     0x10000 /* 64K */
 
+/*
+ * Used to differentiate between relocatable kdump kernel and other
+ * kernels
+ */
+#define KDUMP_SIGNATURE 0xfeed1234
+
 #ifdef CONFIG_CRASH_DUMP
 
 #define KDUMP_TRAMPOLINE_START  0x0100
@@ -19,17 +25,18 @@
 #endif /* CONFIG_CRASH_DUMP */
 
 #ifndef __ASSEMBLY__
-#ifdef CONFIG_CRASH_DUMP
 
+extern unsigned long __kdump_flag;
+
+#if defined(CONFIG_CRASH_DUMP) && !defined(CONFIG_RELOCATABLE)
 extern void reserve_kdump_trampoline(void);
 extern void setup_kdump_trampoline(void);
-
-#else /* !CONFIG_CRASH_DUMP */
-
+#else
+/* !CRASH_DUMP || RELOCATABLE */
 static inline void reserve_kdump_trampoline(void) { ; }
 static inline void setup_kdump_trampoline(void) { ; }
+#endif
 
-#endif /* CONFIG_CRASH_DUMP */
 #endif /* __ASSEMBLY__ */
 
 #endif /* __PPC64_KDUMP_H */