0-day reported this build error:
arch/x86/boot/compressed/pgtable_64.o: In function `l5_paging_required':
pgtable_64.c:(.text+0x22): undefined reference to `__force_order'
The issue is only with GCC < 5 and when KASLR is disabled. Newer GCC
works fine.
__force_order is used by special_insns.h asm code to force instruction
serialization.
It doesn't actually referenced from the code, but GCC < 5 with -fPIE
would still generate undefined symbol.
I didn't noticed this before and failed to move __force_order definition
from pagetable.c (which compiles only with KASLR enabled) to
pgtable_64.c.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Fixes: 10c9a5346f72 ("x86/boot/compressed/64: Detect and handle 5-level paging at boot-time")
Cc: stable@xxxxxxxxxxxxxxx
---
arch/x86/boot/compressed/pagetable.c | 3 ---
arch/x86/boot/compressed/pgtable_64.c | 11 +++++++++++
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
index 6bd51de4475c..250826ac216e 100644
--- a/arch/x86/boot/compressed/pagetable.c
+++ b/arch/x86/boot/compressed/pagetable.c
@@ -38,9 +38,6 @@
#define __PAGE_OFFSET __PAGE_OFFSET_BASE
#include "../../mm/ident_map.c"
-/* Used by pgtable.h asm code to force instruction serialization. */
-unsigned long __force_order;
-
/* Used to track our page table allocation area. */
struct alloc_pgt_data {
unsigned char *pgt_buf;
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 7bcf03b376da..491fa2d08bca 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -1,5 +1,16 @@
#include <asm/processor.h>
+/*
+ * __force_order is used by special_insns.h asm code to force instruction
+ * serialization.
+ *
+ * It doesn't actually referenced from the code, but GCC < 5 with -fPIE
+ * would still generate undefined symbol.
+ *
+ * Let's workaround this by defining the variable.
+ */
+unsigned long __force_order;
+
int l5_paging_required(void)
{
/* Check if leaf 7 is supported. */
--
2.15.0