drivers/clk/clk-k210.c:717:6: warning: variable 'reg' set but not used
Jisheng Zhang
jszhang3 at mail.ustc.edu.cn
Sat Jun 12 06:18:21 PDT 2021
On Fri, 11 Jun 2021 20:55:41 -0700 (PDT)
Palmer Dabbelt <palmerdabbelt at google.com> wrote:
> On Thu, 03 Jun 2021 03:03:14 PDT (-0700), Damien Le Moal wrote:
> >> On 2021/06/03 18:35, kernel test robot wrote:
> >> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> >> head: 324c92e5e0ee0e993bdb106fac407846ed677f6b
> >> commit: c6ca7616f7d5c2ce166280107ba74db1d528fcb7 clk: Add RISC-V Canaan Kendryte K210 clock driver
> >> date: 3 months ago
> >> config: riscv-randconfig-r033-20210603 (attached as .config)
> >> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project d8e0ae9a76a62bdc6117630d59bf9967ac9bb4ea)
> >> 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 riscv cross compiling tool for clang build
> >> # apt-get install binutils-riscv64-linux-gnu
> >> # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c6ca7616f7d5c2ce166280107ba74db1d528fcb7
> >> git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >> git fetch --no-tags linus master
> >> git checkout c6ca7616f7d5c2ce166280107ba74db1d528fcb7
> >> # save the attached .config to linux build tree
> >> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=riscv
> >>
> >> If you fix the issue, kindly add following tag as appropriate
> >> Reported-by: kernel test robot <lkp at intel.com>
> >>
> >> All warnings (new ones prefixed by >>):
> >>
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:556:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> return inb(addr);
> >> ^~~~~~~~~
> >> arch/riscv/include/asm/io.h:55:76: note: expanded from macro 'inb'
> >> #define inb(c) ({ u8 __v; __io_pbr(); __v = readb_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:87:48: note: expanded from macro 'readb_cpu'
> >> #define readb_cpu(c) ({ u8 __r = __raw_readb(c); __r; })
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:564:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> return inw(addr);
> >> ^~~~~~~~~
> >> arch/riscv/include/asm/io.h:56:76: note: expanded from macro 'inw'
> >> #define inw(c) ({ u16 __v; __io_pbr(); __v = readw_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:88:76: note: expanded from macro 'readw_cpu'
> >> #define readw_cpu(c) ({ u16 __r = le16_to_cpu((__force __le16)__raw_readw(c)); __r; })
> >> ^
> >> include/uapi/linux/byteorder/little_endian.h:36:51: note: expanded from macro '__le16_to_cpu'
> >> #define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:572:9: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> return inl(addr);
> >> ^~~~~~~~~
> >> arch/riscv/include/asm/io.h:57:76: note: expanded from macro 'inl'
> >> #define inl(c) ({ u32 __v; __io_pbr(); __v = readl_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:89:76: note: expanded from macro 'readl_cpu'
> >> #define readl_cpu(c) ({ u32 __r = le32_to_cpu((__force __le32)__raw_readl(c)); __r; })
> >> ^
> >> include/uapi/linux/byteorder/little_endian.h:34:51: note: expanded from macro '__le32_to_cpu'
> >> #define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:580:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> outb(value, addr);
> >> ^~~~~~~~~~~~~~~~~
> >> arch/riscv/include/asm/io.h:59:68: note: expanded from macro 'outb'
> >> #define outb(v,c) ({ __io_pbw(); writeb_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:91:52: note: expanded from macro 'writeb_cpu'
> >> #define writeb_cpu(v, c) ((void)__raw_writeb((v), (c)))
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:588:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> outw(value, addr);
> >> ^~~~~~~~~~~~~~~~~
> >> arch/riscv/include/asm/io.h:60:68: note: expanded from macro 'outw'
> >> #define outw(v,c) ({ __io_pbw(); writew_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:92:76: note: expanded from macro 'writew_cpu'
> >> #define writew_cpu(v, c) ((void)__raw_writew((__force u16)cpu_to_le16(v), (c)))
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:596:2: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> outl(value, addr);
> >> ^~~~~~~~~~~~~~~~~
> >> arch/riscv/include/asm/io.h:61:68: note: expanded from macro 'outl'
> >> #define outl(v,c) ({ __io_pbw(); writel_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
> >> ~~~~~~~~~~ ^
> >> arch/riscv/include/asm/mmio.h:93:76: note: expanded from macro 'writel_cpu'
> >> #define writel_cpu(v, c) ((void)__raw_writel((__force u32)cpu_to_le32(v), (c)))
> >> ^
> >> In file included from drivers/clk/clk-k210.c:8:
> >> In file included from include/linux/io.h:13:
> >> In file included from arch/riscv/include/asm/io.h:149:
> >> include/asm-generic/io.h:1005:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> return (port > MMIO_UPPER_LIMIT) ? NULL : PCI_IOBASE + port;
+ Christoph
This warning can only be reproduced with clang + W=1
The problem is that PCI_IOBASE isn't defined for NOMMU, so clang complains
null pointer arithmetic.
> >> ~~~~~~~~~~ ^
> >>>> drivers/clk/clk-k210.c:717:6: warning: variable 'reg' set but not used [-Wunused-but-set-variable]
> >> u32 reg;
> >> ^
> >> 8 warnings generated.
This warning can't be reproduced even with clang + W=1
> >>
> >>
> >> vim +/reg +717 drivers/clk/clk-k210.c
> >>
> >> 710
> >> 711 static int k210_clk_set_parent(struct clk_hw *hw, u8 index)
> >> 712 {
> >> 713 struct k210_clk *kclk = to_k210_clk(hw);
> >> 714 struct k210_sysclk *ksc = kclk->ksc;
> >> 715 struct k210_clk_cfg *cfg = &k210_clk_cfgs[kclk->id];
> >> 716 unsigned long flags;
> >> > 717 u32 reg;
> >
> > Palmer,
> >
> > I do not think this driver is the real cause of this error. Did something change
> > recently with risc-v mmio readl()/writel() ?
>
> I have no idea what's going on here. When I try to re-build that config
> I don't get any warnings or errors. That said...
>
> >> 718
> >> 719 spin_lock_irqsave(&ksc->clk_lock, flags);
> >> 720 reg = readl(ksc->regs + cfg->mux_reg);
> >> 721 if (index)
> >> 722 reg |= BIT(cfg->mux_bit);
> >> 723 else
> >> 724 reg &= ~BIT(cfg->mux_bit);
> >> 725 spin_unlock_irqrestore(&ksc->clk_lock, flags);
>
> Isn't reg unused here? That's one of the warnings.
>
> The void* casting has been there for a while and looks like a real bug,
> but asm-generic adopted our {in,out}{bwlq} implementation so I'm just
> going to toss ours. I'm not quite sure why the generic ones aren't
> doing arithmetic on void*, but I'm not getting warnings.
>
> >> 726
> >> 727 return 0;
> >> 728 }
> >> 729
> >>
> >> ---
> >> 0-DAY CI Kernel Test Service, Intel Corporation
> >> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
> >>
> >
> >
> >--
> >Damien Le Moal
> >Western Digital Research
> >
>
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