Commit 04c17341 authored Jun 19, 2015 by Borislav Petkov Committed by Ingo Molnar Jun 19, 2015

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 <matz@suse.de>
Reported-and-tested-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0f57d867

arch/x86/kernel/head_32.S

+10 −3

Original line number	Diff line number	Diff line
		@@ -62,8 +62,15 @@
		#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

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