x86_64: use correct PAGE_OFFSET

This fixes a bug when using gdb with vmcore
as explained by Dave Anderson:

The kexec/arch/x86_64/crashdump-x86_64.h file contains a
stale PAGE_OFFSET value.  In 2.6.27 it was changed from
0xffff810000000000UL to 0xffff880000000000UL.  This is
only a problem when using gdb with the vmlinux/vmcore
pair, because gdb relies upon the PT_LOAD segment's p_vaddr
values in the ELF header to be correct.

Cc: Dave Anderson <anderson@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

4 files changed, 101 insertions, 11 deletions

diff --git a/kexec/arch/x86_64/Makefile b/kexec/arch/x86_64/Makefile
index 7ca3e7e..e6a8d35 100644
--- a/kexec/arch/x86_64/Makefile
+++ b/kexec/arch/x86_64/Makefile
@@ -13,6 +13,8 @@ x86_64_KEXEC_SRCS += kexec/arch/x86_64/kexec-x86_64.c
 x86_64_KEXEC_SRCS += kexec/arch/x86_64/kexec-elf-x86_64.c
 x86_64_KEXEC_SRCS += kexec/arch/x86_64/kexec-elf-rel-x86_64.c
 
+x86_64_ARCH_INIT = kexec/arch/x86_64/arch_init.c
+
 dist += kexec/arch/x86_64/Makefile $(x86_64_KEXEC_SRCS)			\
 	kexec/arch/x86_64/kexec-x86_64.h kexec/arch/x86_64/crashdump-x86_64.h \
 	kexec/arch/x86_64/include/arch/options.h
diff --git a/kexec/arch/x86_64/arch_init.c b/kexec/arch/x86_64/arch_init.c
new file mode 100644
index 0000000..79fb642
--- /dev/null
+++ b/kexec/arch/x86_64/arch_init.c
@@ -0,0 +1,83 @@
+#include <errno.h>
+#include <string.h>
+#include <sys/utsname.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <stdio.h>
+
+#include "crashdump-x86_64.h"
+
+#define KERNEL_VERSION(major, minor, patch) \
+	(((major) << 16) | ((minor) << 8) | patch)
+
+long kernel_version(void)
+{
+	struct utsname utsname;
+	unsigned long major, minor, patch;
+	char *p;
+
+	if (uname(&utsname) < 0) {
+		fprintf(stderr, "uname failed: %s\n", strerror(errno));
+		return -1;
+	}
+
+	p = utsname.release;
+	major = strtoul(p, &p, 10);
+	if (major == ULONG_MAX) {
+		fprintf(stderr, "strtoul failed: %s\n", strerror(errno));
+		return -1;
+	}
+
+	if (*p++ != '.') {
+		fprintf(stderr, "Unsupported utsname.release: %s\n",
+			utsname.release);
+		return -1;
+	}
+
+	minor = strtoul(p, &p, 10);
+	if (major == ULONG_MAX) {
+		fprintf(stderr, "strtoul failed: %s\n", strerror(errno));
+		return -1;
+	}
+
+	if (*p++ != '.') {
+		fprintf(stderr, "Unsupported utsname.release: %s\n",
+			utsname.release);
+		return -1;
+	}
+
+	patch = strtoul(p, &p, 10);
+	if (major == ULONG_MAX) {
+		fprintf(stderr, "strtoul failed: %s\n", strerror(errno));
+		return -1;
+	}
+
+	if (major >= 256 || minor >= 256 || patch >= 256) {
+		fprintf(stderr, "Unsupported utsname.release: %s\n",
+			utsname.release);
+		return -1;
+	}
+
+	return KERNEL_VERSION(major, minor, patch);
+}
+
+#define PAGE_OFFSET_PRE_2_6_27	0xffff810000000000UL
+#define PAGE_OFFSET		0xffff880000000000UL
+
+unsigned long page_offset;
+
+int arch_init(void)
+{
+	int kv;
+
+	kv = kernel_version();
+	if (kv < 0)
+		return -1;
+
+	if (kv < KERNEL_VERSION(2, 6, 27))
+		page_offset = PAGE_OFFSET_PRE_2_6_27;
+	else
+		page_offset = PAGE_OFFSET;
+
+	return 0;
+}
diff --git a/kexec/arch/x86_64/crashdump-x86_64.c b/kexec/arch/x86_64/crashdump-x86_64.c
index b6b410b..29e9602 100644
--- a/kexec/arch/x86_64/crashdump-x86_64.c
+++ b/kexec/arch/x86_64/crashdump-x86_64.c
@@ -36,15 +36,6 @@
 #include "crashdump-x86_64.h"
 #include <x86/x86-linux.h>
 
-static struct crash_elf_info elf_info =
-{
-	class: ELFCLASS64,
-	data: ELFDATA2LSB,
-	machine: EM_X86_64,
-	backup_src_start: BACKUP_SRC_START,
-	backup_src_end: BACKUP_SRC_END,
-	page_offset: PAGE_OFFSET,
-};
 
 /* Forward Declaration. */
 static int exclude_region(int *nr_ranges, uint64_t start, uint64_t end);
@@ -604,6 +595,16 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
 	int nr_ranges, align = 1024, i;
 	struct memory_range *mem_range, *memmap_p;
 
+	struct crash_elf_info elf_info =
+	{
+		class: ELFCLASS64,
+		data: ELFDATA2LSB,
+		machine: EM_X86_64,
+		backup_src_start: BACKUP_SRC_START,
+		backup_src_end: BACKUP_SRC_END,
+		page_offset: page_offset,
+	};
+
 	if (get_kernel_paddr(info))
 		return -1;
 
diff --git a/kexec/arch/x86_64/crashdump-x86_64.h b/kexec/arch/x86_64/crashdump-x86_64.h
index 0e83527..2129104 100644
--- a/kexec/arch/x86_64/crashdump-x86_64.h
+++ b/kexec/arch/x86_64/crashdump-x86_64.h
@@ -1,12 +1,16 @@
 #ifndef CRASHDUMP_X86_64_H
 #define CRASHDUMP_X86_64_H
 
+#include "../../kexec.h"
+
 int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
 				unsigned long max_addr, unsigned long min_base);
 
 #define __START_KERNEL_map      0xffffffff80000000UL
-#define PAGE_OFFSET		0xffff810000000000UL
-#define __pa(x)                 (((unsigned long)(x)>=__START_KERNEL_map)?(unsigned long)(x) - (unsigned long)__START_KERNEL_map:(unsigned long)(x) - PAGE_OFFSET)
+
+extern unsigned long page_offset;
+
+#define __pa(x)                 (((unsigned long)(x)>=__START_KERNEL_map)?(unsigned long)(x) - (unsigned long)__START_KERNEL_map:(unsigned long)(x) - page_offset)
 
 #define MAXMEM           0x3fffffffffffUL