* Kirill A. Shutemov kirill.shutemov@linux.intel.com wrote:

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.

s/is used by special_insns.h asm code /is used by the special_insns.h asm code

It doesn't actually referenced from the code, but GCC < 5 with -fPIE would still generate undefined symbol.

s/It doesn't actually referenced from the code /It isn't actually referenced from the code

s/would still generate undefined symbol. /would still generate an 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@linux.intel.com Fixes: 10c9a5346f72 ("x86/boot/compressed/64: Detect and handle 5-level paging at boot-time") Cc: stable@vger.kernel.org

---

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.

s/is used by special_insns.h asm code /is used by the special_insns.h asm code

• • It doesn't actually referenced from the code, but GCC < 5 with -fPIE
• • would still generate undefined symbol.

s/It doesn't actually referenced from the code /It isn't actually referenced from the code

s/would still generate undefined symbol. /would still generate an undefined symbol.

• • Let's workaround this by defining the variable.

s/Let's workaround /Let's work around

Also, for the title:

s/Fix build with GCC < 5 /Fix the build with GCC < 5

Thanks,

Ingo