Re: [PATCH v5 5/5] powerpc/inst: Optimise copy_inst_from_kernel_nofault()

Christophe Leroy
2021-11-30T05:58:31Z

Le 29/11/2021 à 23:55, kernel test robot a écrit :
> Hi Christophe,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on powerpc/next]
> [also build test WARNING on v5.16-rc3 next-20211129]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
>
> url: https://github.com/0day-ci/linux/commits/Christophe-Leroy/powerpc-inst-Refactor-___get_user_instr/20211130-015346
> base: https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
> config: powerpc-randconfig-r023-20211129 (https://download.01.org/0day-ci/archive/20211130/202111300652.0yDBNvyJ-lkp@intel.com/config)
> compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project df08b2fe8b35cb63dfb3b49738a3494b9b4e6f8e)
> reproduce (this is a W=1 build):
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # install powerpc cross compiling tool for clang build
> # apt-get install binutils-powerpc-linux-gnu
> # https://github.com/0day-ci/linux/commit/fb7bff30cc0efc7e4df1b48bb69de1f325eee826
> git remote add linux-review https://github.com/0day-ci/linux
> git fetch --no-tags linux-review Christophe-Leroy/powerpc-inst-Refactor-___get_user_instr/20211130-015346
> git checkout fb7bff30cc0efc7e4df1b48bb69de1f325eee826
> # save the config file to linux build tree
> mkdir build_dir
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc prepare
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
> In file included from arch/powerpc/kernel/asm-offsets.c:71:
> In file included from arch/powerpc/kernel/../xmon/xmon_bpts.h:7:
>>> arch/powerpc/include/asm/inst.h:165:20: warning: variable 'val' is uninitialized when used here [-Wuninitialized]
> *inst = ppc_inst(val);
> ^~~
> arch/powerpc/include/asm/inst.h:53:22: note: expanded from macro 'ppc_inst'
> #define ppc_inst(x) (x)
> ^
> arch/powerpc/include/asm/inst.h:155:18: note: initialize the variable 'val' to silence this warning
> unsigned int val, suffix;
> ^
> = 0

I can't understand what's wrong here.

We have

__get_kernel_nofault(&val, src, u32, Efault);
if (IS_ENABLED(CONFIG_PPC64) && get_op(val) == OP_PREFIX) {
__get_kernel_nofault(&suffix, src + 1, u32, Efault);
*inst = ppc_inst_prefix(val, suffix);
} else {
*inst = ppc_inst(val);
}

With

#define __get_kernel_nofault(dst, src, type, err_label) \
__get_user_size_goto(*((type *)(dst)), \
(__force type __user *)(src), sizeof(type), err_label)

And

#define __get_user_size_goto(x, ptr, size, label) \
do { \
BUILD_BUG_ON(size > sizeof(x)); \
switch (size) { \
case 1: __get_user_asm_goto(x, (u8 __user *)ptr, label, "lbz"); break; \
case 2: __get_user_asm_goto(x, (u16 __user *)ptr, label, "lhz"); break; \
case 4: __get_user_asm_goto(x, (u32 __user *)ptr, label, "lwz"); break; \
case 8: __get_user_asm2_goto(x, (u64 __user *)ptr, label); break; \
default: x = 0; BUILD_BUG(); \
} \
} while (0)

And

#define __get_user_asm_goto(x, addr, label, op) \
asm_volatile_goto( \
"1: "op"%U1%X1 %0, %1 # get_user\n" \
EX_TABLE(1b, %l2) \
: "=r" (x) \
: "m<>" (*addr) \
: \
: label)

I see no possibility, no alternative path where val wouldn't be set. The
asm clearly has *addr as an output param so it is always set.

> 1 warning generated.
> <stdin>:1559:2: warning: syscall futex_waitv not implemented [-W#warnings]
> #warning syscall futex_waitv not implemented
> ^
> 1 warning generated.
> arch/powerpc/kernel/vdso32/gettimeofday.S:72:8: error: unsupported directive '.stabs'
> .stabs "_restgpr_31_x:F-1",36,0,0,_restgpr_31_x; .globl _restgpr_31_x; _restgpr_31_x:
> ^
> arch/powerpc/kernel/vdso32/gettimeofday.S:73:8: error: unsupported directive '.stabs'
> .stabs "_rest32gpr_31_x:F-1",36,0,0,_rest32gpr_31_x; .globl _rest32gpr_31_x; _rest32gpr_31_x:

How should we fix that ? Will clang support .stabs in the future ?

> ^
> make[2]: *** [arch/powerpc/kernel/vdso32/Makefile:55: arch/powerpc/kernel/vdso32/gettimeofday.o] Error 1
> make[2]: Target 'include/generated/vdso32-offsets.h' not remade because of errors.
> make[1]: *** [arch/powerpc/Makefile:421: vdso_prepare] Error 2
> make[1]: Target 'prepare' not remade because of errors.
> make: *** [Makefile:219: __sub-make] Error 2
> make: Target 'prepare' not remade because of errors.
>
>
> vim +/val +165 arch/powerpc/include/asm/inst.h
>
> 152
> 153 static inline int copy_inst_from_kernel_nofault(ppc_inst_t *inst, u32 *src)
> 154 {
> 155 unsigned int val, suffix;
> 156
> 157 if (unlikely(!is_kernel_addr((unsigned long)src)))
> 158 return -ERANGE;
> 159
> 160 __get_kernel_nofault(&val, src, u32, Efault);
> 161 if (IS_ENABLED(CONFIG_PPC64) && get_op(val) == OP_PREFIX) {
> 162 __get_kernel_nofault(&suffix, src + 1, u32, Efault);
> 163 *inst = ppc_inst_prefix(val, suffix);
> 164 } else {
> > 165 *inst = ppc_inst(val);
> 166 }
> 167 return 0;
> 168 Efault:
> 169 return -EFAULT;
> 170 }
> 171
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>