[Makedumpfile PATCH v2 2/2] x86_64: calculate page_offset in case of re-filtering

[Pratyush Anand]

we do not call get_elf_info() in case of refiltering. Therefore, we will
not have any pt_load in that case, and so we get:

get_page_offset_x86_64: Can't get any pt_load to calculate page offset.

However, we will have vmcoreinfo and vmlinux information in case of
re-filtering. So, we are able to find kaslr offset and we can get
page_offset_base address. Thus we can read the page offset as well.
However, if kaslr is not enabled then use old method to find fixed page
offset.

Signed-off-by: Pratyush Anand <panand at redhat.com>
---
 arch/x86_64.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86_64.c b/arch/x86_64.c
index 3116811d7563..8a50998aa470 100644
--- a/arch/x86_64.c
+++ b/arch/x86_64.c
@@ -75,6 +75,7 @@ get_page_offset_x86_64(void)
 	int i;
 	unsigned long long phys_start;
 	unsigned long long virt_start;
+	unsigned long page_offset_base;
 
 	for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) {
 		if (virt_start < __START_KERNEL_map
@@ -84,8 +85,25 @@ get_page_offset_x86_64(void)
 		}
 	}
 
-	ERRMSG("Can't get any pt_load to calculate page offset.\n");
-	return FALSE;
+	if (!info->flag_refiltering) {
+		ERRMSG("Can't get any pt_load to calculate page offset.\n");
+		return FALSE;
+	}
+	if (info->kaslr_offset) {
+		page_offset_base = get_symbol_addr("page_offset_base");
+		page_offset_base += info->kaslr_offset;
+		if (!readmem(VADDR, page_offset_base, &info->page_offset,
+					sizeof(info->page_offset))) {
+			 ERRMSG("Can't read page_offset_base.\n");
+			 return FALSE;
+		}
+	} else if (info->kernel_version < KERNEL_VERSION(2, 6, 27)) {
+		info->page_offset = __PAGE_OFFSET_ORIG;
+	} else {
+		info->page_offset = __PAGE_OFFSET_2_6_27;
+	}
+
+	return TRUE;
 }
 
 int
-- 
2.9.3