linux-kernel - Re: X86 GIT GCC 5 compilation warning

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Message-ID: <20150616135801.GH17786@pd.tnic>
Date:	Tue, 16 Jun 2015 15:58:01 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Enrico Mioso <mrkiko.rs@...il.com>
Cc:	Michael Matz <matz@...e.de>, linux-kernel@...r.kernel.org,
	x86-ml <x86@...nel.org>
Subject: Re: X86 GIT GCC 5 compilation warning

On Tue, Jun 16, 2015 at 02:47:02PM +0200, Michael Matz wrote:
> Yeah, building like so on i686 will produce an assembler that warns on 
> "1<<32".

Enrico, try this.

---
From: Borislav Petkov <bp@...e.de>
Date: Tue, 16 Jun 2015 15:43:27 +0200
Subject: [PATCH] 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-by: Enrico Mioso <mrkiko.rs@...il.com>
Suggested-by: Michael Matz <matz@...e.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/head_32.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 53eeb226657c..c601d1de5ae5 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -63,8 +63,8 @@
 #endif
 
 /* Number of possible pages in the lowmem region */
-LOWMEM_PAGES = (((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT)
-	
+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.
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