[Crash-utility] Fix loading qemu's dump-guest-image

[OGAWA Hirofumi]

qemu can make elf vmcore without kdump in kernel. So kernel may not
have "kexec_crash_image" symbol.

Without this patch, kdump_backup_region_init() stops main_loop with
error.

---

 netdump.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff -puN netdump.c~check-kexec_crash_image netdump.c
--- crash-64/netdump.c~check-kexec_crash_image	2016-03-29 19:38:08.556253626 +0900
+++ crash-64-hirofumi/netdump.c	2016-03-29 19:38:08.557253630 +0900
@@ -4458,11 +4458,14 @@ kdump_backup_region_init(void)
 	} else
 		return;
 
-	if (!readmem(symbol_value("kexec_crash_image"), KVADDR,
-		     &kexec_crash_image_p, sizeof(ulong),
-		     "kexec backup region: kexec_crash_image",
-		     QUIET|RETURN_ON_ERROR))
-		goto error;
+	if (symbol_exists("kexec_crash_image")) {
+		if (!readmem(symbol_value("kexec_crash_image"), KVADDR,
+			     &kexec_crash_image_p, sizeof(ulong),
+			     "kexec backup region: kexec_crash_image",
+			     QUIET|RETURN_ON_ERROR))
+			goto error;
+	} else
+		kexec_crash_image_p = 0;
 
 	if (!kexec_crash_image_p) {
 		if (CRASHDEBUG(1))
_

-- 
OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>