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

Christophe Leroy [off-list ref] writes:

Le 29/11/2021 à 23:55, kernel test robot a écrit :

quoted

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 <redacted>

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:

quoted

quoted

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.

I guess clang can't convince itself of that?

quoted

    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 ?

I think we should drop any stabs annotations / support. AFAICT none of
the toolchains we support produce it anymore.

cheers