On Fri, Jun 19, 2015 at 12:46:28PM +0200, Ingo Molnar wrote: > Grumble. I guess the workaround is OK then because I cannot think > of any cleaner solution - but I'd suggest to put a comment there at > minimum, to explain what it's about. > > ... and chances are that GAS might start warning about 2<<31 in the > future as well.
Reportedly it won't because it'll wrap around to 0 and that is fine... Anyway, here's v2: --- From: Borislav Petkov <[email protected]> Subject: [PATCH -v2] x86/head_32: 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. Reported-and-tested-by: Enrico Mioso <[email protected]> Suggested-by: Michael Matz <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> --- arch/x86/kernel/head_32.S | 13 ++++++++++--- 1 file 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 -- 2.3.5 -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
