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charset=utf-8 Content-Transfer-Encoding: quoted-printable tree: https://github.com/intel-lab-lkp/linux/commits/Eduard-Zingerman/bpf= -track-may_write-flags-in-liveness/20260926-071959 head: 588faaac20422c91861700e863668674da9cc06f commit: 280ac823486cf3ef2a002b680a99c1e162a16204 bpf: use SCEV to widen bou= nded loops date: 5 days ago config: i386-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20261= 001/202610011731.DcYbvUbx-lkp@intel.com/config) compiler: gcc-14 (Debian 14.2.0-19) 14.2.0 reproduce (this is a W=3D1 build): (https://download.01.org/0day-ci/archive= /20261001/202610011731.DcYbvUbx-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new versio= n of the same patch/commit), kindly add following tags | Reported-by: kernel test robot | Closes: https://lore.kernel.org/oe-kbuild-all/202610011731.DcYbvUbx-lkp@i= ntel.com/ All errors (new ones prefixed by >>): ld: kernel/bpf/verifier.o: in function `scalar_step_lsh': kernel/bpf/verifier.c:15665:(.text+0x149c2): undefined reference to `__u= moddi3' ld: kernel/bpf/verifier.o: in function `scalar_step_mul': kernel/bpf/verifier.c:15654:(.text+0x15c36): undefined reference to `__u= moddi3' ld: kernel/bpf/scev.o: in function `compute_max_iters': >> kernel/bpf/scev.c:1736:(.text+0xf7b): undefined reference to `__udivmodd= i4' vim +1736 kernel/bpf/scev.c 1681=09 1682 /* 1683 * Loop with post-condition: 1684 * 1685 * r0 =3D 0 1686 * l: ... r0 =E2=88=88 [0,1,2] header executed 3 times 1687 * r0 +=3D 1 r0 =E2=88=88 [0,1,2] 1688 * ... r0 =E2=88=88 [1,2,3] 1689 * if r0 !=3D 3 goto l r0 =E2=88=88 [1,2,3] backedge taken 2 tim= es 1690 * ... r0 =E2=88=88 [3] 1691 * 1692 * SCEV at header: r0 =3D k 1693 * SCEV at latch: r0 =3D 1 + k 1694 * 1695 * Loop with pre-condition: 1696 * 1697 * r0 =3D 0 1698 * l: ... r0 =E2=88=88 [0,1,2,3] header executed 4 ti= mes 1699 * if r0 =3D=3D 3 goto e r0 =E2=88=88 [0,1,2,3] backedge taken 3= times 1700 * r0 +=3D 1 r0 =E2=88=88 [0,1,2] 1701 * ... r0 =E2=88=88 [1,2,3] 1702 * goto l r0 =E2=88=88 [1,2,3] 1703 * e: ... r0 =E2=88=88 [3] 1704 * 1705 * SCEV at header: r0 =3D k 1706 * SCEV at latch: r0 =3D k 1707 */ 1708 static bool compute_max_iters(struct bpf_verifier_env *env, 1709 struct bpf_func_state *st, 1710 struct linear_latch *latch, 1711 struct bpf_loop_iters *iters) 1712 { 1713 u64 base, step, diff, bound, initial, max_iters; 1714 struct bpf_insn_aux_data *aux =3D env->insn_aux_data; 1715 struct bpf_loop *loop =3D aux[bpf_loop_at_index(env, latch->insn_id= x)].loop; 1716 struct scev *scev =3D env->scev; 1717 u8 op =3D latch->op; 1718=09 1719 if (!eval_expr(env, scev, st, latch->base_expr, &base) || 1720 !eval_expr(env, scev, st, latch->step_expr, &step) || 1721 !eval_expr(env, scev, st, latch->bound_expr, &bound) || 1722 !eval_expr(env, scev, st, latch->reg_expr, &initial)) 1723 return false; 1724=09 1725 if (step =3D=3D 0) 1726 return false; 1727 if ((s64)step =3D=3D S64_MIN) 1728 return false; 1729 if ((s64)step < 0) { 1730 /* Multiply both sides of the equation by -1, e.g. -2*i > -3 becom= es 2*i < 3 */ 1731 op =3D bpf_flip_opcode(op); 1732 step =3D -step; 1733 swap(bound, initial); 1734 } 1735 diff =3D bound - initial; > 1736 if (diff / step =3D=3D U64_MAX) 1737 return false; 1738 switch (op) { 1739 case BPF_JLT: 1740 max_iters =3D (u64)initial >=3D (u64)bound ? 0 : div_round_up(diff= , step); 1741 break; 1742 case BPF_JLE: 1743 max_iters =3D (u64)initial > (u64)bound ? 0 : diff / step + 1; 1744 break; 1745 case BPF_JSLT: 1746 max_iters =3D (s64)initial >=3D (s64)bound ? 0 : div_round_up(diff= , step); 1747 break; 1748 case BPF_JSLE: 1749 max_iters =3D (s64)initial > (s64)bound ? 0 : diff / step + 1; 1750 break; 1751 case BPF_JNE: 1752 max_iters =3D diff % step ? U32_MAX : div_round_up(diff, step); 1753 break; 1754 default: 1755 return false; 1756 } 1757=09 1758 if (max_iters > U32_MAX) 1759 return false; 1760=09 1761 /* 1762 * The latch is a conditional jump with one jump target exiting the= loop. 1763 * Linear latch is matched only if the loop has a single backedge. 1764 * The loop still, however can have multiple exits. 1765 * In such case, conservatively assume that non-latch exit can happ= en 1766 * at any iteration, thus setting minimal number of iterations as 0. 1767 */ 1768 iters->max_header_count =3D max_iters + (base =3D=3D 0 ? 1 : 0); 1769 iters->min_header_count =3D loop->exits_cnt =3D=3D 1 ? iters->max_h= eader_count : 0; 1770 iters->pre_cond =3D base =3D=3D 0; 1771 return true; 1772 } 1773=09 -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki