[Xen-devel] [PATCH] x86: fix LOWMEM_PAGES constant

[Arnd Bergmann <arnd@xxxxxxxx>]

clang points out that the computation of LOWMEM_PAGES causes
a signed integer overflow on 32-bit x86:

arch/x86/kernel/head32.c:83:20: error: signed shift result (0x100000000) 
requires 34 bits to represent, but 'int' only has 32 bits 
[-Werror,-Wshift-overflow]
                (PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT);
                                 ^~~~~~~~~~~~
arch/x86/include/asm/pgtable_32.h:109:27: note: expanded from macro 
'LOWMEM_PAGES'
 #define LOWMEM_PAGES ((((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
                         ~^ ~~
arch/x86/include/asm/pgtable_32.h:98:34: note: expanded from macro 
'PAGE_TABLE_SIZE'
 #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)

Use the _ULL() macro to make it a 64-bit constant.

Fixes: 1e620f9b23e5 ("x86/boot/32: Convert the 32-bit pgtable setup code from 
assembly to C")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 arch/x86/include/asm/pgtable_32.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable_32.h 
b/arch/x86/include/asm/pgtable_32.h
index 4fe9e7fc74d3..c78da8eda8f2 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -106,6 +106,6 @@ do {                                                \
  * with only a host target support using a 32-bit type for internal
  * representation.
  */
-#define LOWMEM_PAGES ((((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
+#define LOWMEM_PAGES ((((_ULL(2)<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
 
 #endif /* _ASM_X86_PGTABLE_32_H */
-- 
2.20.0


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