x86/boot: Fix overflow warning with 32-bit binutils

When building the kernel with 32-bit binutils built with support
only for the i386 target, we get the following warning:

  arch/x86/kernel/head_32.S:66: Warning: shift count out of range (32 is not between 0 and 31)

The problem is that in that case, binutils' internal type
representation is 32-bit wide and the shift range overflows.

In order to fix this, manipulate the shift expression which
creates the 4GiB constant to not overflow the shift count.

Suggested-by: Michael Matz <[email protected]>
Reported-and-tested-by: Enrico Mioso <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 10 insertions, 3 deletions

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 53eeb226657c..7e429c99c728 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -62,9 +62,16 @@
 #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
 #endif
 
-/* Number of possible pages in the lowmem region */
-LOWMEM_PAGES = (((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT)
-	
+/*
+ * Number of possible pages in the lowmem region.
+ *
+ * We shift 2 by 31 instead of 1 by 32 to the left in order to avoid a
+ * gas warning about overflowing shift count when gas has been compiled
+ * with only a host target support using a 32-bit type for internal
+ * representation.
+ */
+LOWMEM_PAGES = (((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT)
+
 /* Enough space to fit pagetables for the low memory linear map */
 MAPPING_BEYOND_END = PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT