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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>
hifive-unleashed-5.1
Borislav Petkov 2015-06-19 13:49:06 +02:00 committed by Ingo Molnar
parent 0f57d86787
commit 04c17341b4
1 changed files with 10 additions and 3 deletions
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13
arch/x86/kernel/head_32.S
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@ -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