Hi Akira, Thank you for the patch! Perhaps something to improve: [auto build test WARNING on linus/master] [also build test WARNING on v5.15 next-20211111] [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/Akira-Tsukamoto/__asm_copy_to-fr... base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git debe436e77c72fcee804fb867f275e6d31aa999c config: riscv-allyesconfig (attached as .config) compiler: riscv64-linux-gcc (GCC) 11.2.0 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 # https://github.com/0day-ci/linux/commit/cf2e8e9c4e9dc65552ca5ac0c85c19878... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Akira-Tsukamoto/__asm_copy_to-from_user-Reduce-more-byte_copy/20211111-161445 git checkout cf2e8e9c4e9dc65552ca5ac0c85c198785f5d91c # save the attached .config to linux build tree mkdir build_dir COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=riscv SHELL=/bin/bash If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): arch/riscv/lib/uaccess.S: Assembler messages: arch/riscv/lib/uaccess.S:94: Warning: zero assumed for missing expression vim +92 arch/riscv/lib/uaccess.S 17 18 /* Enable access to user memory */ 19 li t6, SR_SUM 20 csrs CSR_STATUS, t6 21 22 /* Save for return value */ 23 mv t5, a2 24 25 /* 26 * Register allocation for code below: 27 * a0 - start of uncopied dst 28 * a1 - start of uncopied src 29 * a2 - size 30 * t0 - end of uncopied dst 31 */ 32 add t0, a0, a2 33 34 /* 35 * Use byte copy only if too small. 36 * SZREG holds 4 for RV32 and 8 for RV64 37 * a3 - 2*SZREG is minimum size for word_copy 38 * 1*SZREG for aligning dst + 1*SZREG for word_copy 39 */ 40 li a3, 2*SZREG 41 bltu a2, a3, .Lbyte_copy_tail 42 43 /* 44 * Copy first bytes until dst is aligned to word boundary. 45 * a0 - start of dst 46 * t1 - start of aligned dst 47 */ 48 addi t1, a0, SZREG-1 49 andi t1, t1, ~(SZREG-1) 50 /* dst is already aligned, skip */ 51 beq a0, t1, .Lskip_align_dst 52 1: 53 /* a5 - one byte for copying data */ 54 fixup lb a5, 0(a1), 10f 55 addi a1, a1, 1 /* src */ 56 fixup sb a5, 0(a0), 10f 57 addi a0, a0, 1 /* dst */ 58 bltu a0, t1, 1b /* t1 - start of aligned dst */ 59 60 .Lskip_align_dst: 61 /* 62 * Now dst is aligned. 63 * Use shift-copy if src is misaligned. 64 * Use word-copy if both src and dst are aligned because 65 * can not use shift-copy which do not require shifting 66 */ 67 /* a1 - start of src */ 68 andi a3, a1, SZREG-1 69 bnez a3, .Lshift_copy 70 71 .Lcheck_size_bulk: 72 /* 73 * Evaluate the size if possible to use unrolled. 74 * The word_copy_unlrolled requires larger than 8*SZREG 75 */ 76 li a3, 8*SZREG 77 add a4, a0, a3 78 bltu a4, t0, .Lword_copy_unlrolled 79 80 .Lword_copy: 81 /* 82 * Both src and dst are aligned 83 * Not unrolled word copy with every 1*SZREG iteration 84 * 85 * a0 - start of aligned dst 86 * a1 - start of aligned src 87 * t0 - end of aligned dst 88 */ 89 bgeu a0, t0, .Lbyte_copy_tail /* check if end of copy */ 90 addi t0, t0, -(SZREG) /* not to over run */ 91 1: 93 addi a1, a1, SZREG 94 fixup REG_S a5, 0(a0) 95 addi a0, a0, SZREG 96 bltu a0, t0, 1b 97 98 addi t0, t0, SZREG /* revert to original value */ 99 j .Lbyte_copy_tail 100 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org