On 04/30/2018 12:57 PM, Roger Pau Monné wrote:
On Mon, Apr 30, 2018 at 12:23:36PM -0400, Boris Ostrovsky wrote:
Latest binutils release (2.29.1) will no longer allow proper computation of GDT entries on 32-bits, with warning:
arch/x86/xen/xen-pvh.S: Assembler messages: arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (32 is not between 0 and 31) arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (40 is not between 0 and 31) arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (32 is not between 0 and 31) arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (32 is not between 0 and 31) arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (40 is not between 0 and 31) arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (32 is not between 0 and 31)
Use explicit value of the entry instead of using GDT_ENTRY() macro.
Signed-off-by: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: stable@vger.kernel.org
arch/x86/xen/xen-pvh.S | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S index e1a5fbe..934f7d4 100644 --- a/arch/x86/xen/xen-pvh.S +++ b/arch/x86/xen/xen-pvh.S @@ -145,11 +145,11 @@ gdt_start: .quad 0x0000000000000000 /* NULL descriptor */ .quad 0x0000000000000000 /* reserved */ #ifdef CONFIG_X86_64
- .quad GDT_ENTRY(0xa09a, 0, 0xfffff) /* __KERNEL_CS */
- .quad 0x00af9a000000ffff /* __BOOT_CS */
#else
- .quad GDT_ENTRY(0xc09a, 0, 0xfffff) /* __KERNEL_CS */
- .quad 0x00cf9a000000ffff /* __BOOT_CS */
Maybe it would be cleaner to use something like:
I actually considered all of these and ended up with a raw number because it seems to be a convention in kernel (and Xen too, apparently) to use raw values in .S files.
Kernel is using now GDT_ENTRY_INIT() which is a C macro. There is one other location where GDT_INIT() is used (arch/x86/boot/pm.c) and, incidentally, it also generates this warning IIRC.
I really don't want to move definition to C code just to use a macro --- I don't think C code needs to be exposed to this GDT.
.word 0xffff /* limit */ .word 0 /* base */ .byte 0 /* base */ .byte 0x9a /* access */ #ifdef CONFIG_X86_64 .byte 0xaf /* flags plus limit */ #else .byte 0xcf /* flags plus limit */ #endif .byte 0 /* base */
I, in fact, started with something like this. But if you repeat this 4 times you will probably see why I decided against it ;-)
-boris
Or try to fix the GDT_ENTRY macro, maybe if you prepend extra 0's to make the values 64bit that would prevent the warnings?
Or declare the GDT in enlighten_pvh in C and use it here?
Also, IIRC the base/limit values are ignored in long mode.
Thanks, Roger.