El Thu, Jul 13, 2017 at 11:20:04PM +0300 Andrey Rybainin ha dit: > On 07/13/2017 09:47 PM, Matthias Kaehlcke wrote: > > > Thanks for your analysis! > > > >> What happens if you try the below patch instead of the revert? Any > >> chance the offending instruction goes away? > >> > >> diff --git a/arch/x86/include/asm/uaccess.h > >> b/arch/x86/include/asm/uaccess.h > >> index 11433f9..beac907 100644 > >> --- a/arch/x86/include/asm/uaccess.h > >> +++ b/arch/x86/include/asm/uaccess.h > >> @@ -171,7 +171,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > > >> sizeof(0UL), 0ULL, 0UL)) > >> might_fault(); \ > >> asm volatile("call __get_user_%P4" \ > >> : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ > >> - : "0" (ptr), "i" (sizeof(*(ptr)))); \ > >> + : "0" (ptr), "i" (sizeof(*(ptr))), "r" (__sp)); \ > >> (x) = (__force __typeof__(*(ptr))) __val_gu; \ > >> __builtin_expect(__ret_gu, 0); \ > >> }) > > > > The generated code is basically the same, only that now the value from > > the stack is stored in a register and written twice to RSP: > > > > AFAIR clang works much better with global named registers. > Could you check if the patch bellow helps? > > > --- > arch/x86/include/asm/uaccess.h | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > index a059aac9e937..121204387978 100644 > --- a/arch/x86/include/asm/uaccess.h > +++ b/arch/x86/include/asm/uaccess.h > @@ -157,15 +157,18 @@ __typeof__(__builtin_choose_expr(sizeof(x) > > sizeof(0UL), 0ULL, 0UL)) > * Clang/LLVM cares about the size of the register, but still wants > * the base register for something that ends up being a pair. > */ > + > +register unsigned long __current_sp asm(_ASM_SP); > + > #define get_user(x, ptr) \ > ({ \ > int __ret_gu; \ > register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \ > - register void *__sp asm(_ASM_SP); \ > __chk_user_ptr(ptr); \ > might_fault(); \ > asm volatile("call __get_user_%P4" \ > - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ > + : "=a" (__ret_gu), "=r" (__val_gu), \ > + "+r" (__current_sp) \ > : "0" (ptr), "i" (sizeof(*(ptr)))); \ > (x) = (__force __typeof__(*(ptr))) __val_gu; \ > __builtin_expect(__ret_gu, 0); \
Thanks for the suggestion, however it fails to build with both gcc and clang: fs/ioctl.c:585:6: error: use of undeclared identifier '__current_sp' if (get_user(count, &argp->dest_count)) { ^ arch/x86/include/asm/uaccess.h:168:16: note: expanded from macro 'get_user' "+r" (__current_sp) \ The references I found refer to __current_sp as an intrinsic function for ARM32.