On Tue, Feb 01, 2022, kernel test robot wrote:
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>
> All errors (new ones prefixed by >>):
>
> In file included from arch/x86/kvm/mmu/mmu.c:4246:
> >> arch/x86/kvm/mmu/paging_tmpl.h:244:9: error: invalid output size for constraint '+a'
> ret = __try_cmpxchg_user(ptep_user, &orig_pte, pte, fault);
> ^
> arch/x86/include/asm/uaccess.h:629:11: note: expanded from macro '__try_cmpxchg_user'
> __ret = !unsafe_try_cmpxchg_user(_ptr, _oldp, _nval, _label); \
> ^
> arch/x86/include/asm/uaccess.h:606:18: note: expanded from macro 'unsafe_try_cmpxchg_user'
> case 1: __ret = __try_cmpxchg_user_asm("b", "q", \
> ^
> arch/x86/include/asm/uaccess.h:467:22: note: expanded from macro '__try_cmpxchg_user_asm'
> [old] "+a" (__old) \
#$*&(#$ clang.
clang isn't smart enough to avoid compiling the impossible conditions it will
throw away in the end, i.e. it compiles all cases given:
switch (8) {
case 1:
case 2:
case 4:
case 8:
}
I can fudge around that by casting the pointer, which I don't think can go sideways
if the pointer value is a signed type?
@@ -604,15 +602,15 @@ extern void __try_cmpxchg_user_wrong_size(void);
bool __ret; \
switch (sizeof(*(_ptr))) { \
case 1: __ret = __try_cmpxchg_user_asm("b", "q", \
- (_ptr), (_oldp), \
+ (u8 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 2: __ret = __try_cmpxchg_user_asm("w", "r", \
- (_ptr), (_oldp), \
+ (u16 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 4: __ret = __try_cmpxchg_user_asm("l", "r", \
- (_ptr), (_oldp), \
+ (u32 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 8: __ret = __try_cmpxchg64_user_asm((_ptr), (_oldp), \
clang also lacks the intelligence to realize that it can/should use a single
register for encoding the memory operand and consumes both ESI and EDI, leaving
no register for the __err "+r" param in __try_cmpxchg64_user_asm(). That can be
avoided by open coding CC_SET and using a single output register for both the
result and the -EFAULT error path.
