Re: [PATCH bpf-next v2 2/6] bpf, x86: Add 64-bit bitops kfuncs support for x86_64

From: Leon Hwang

Date: Fri Feb 20 2026 - 09:14:25 EST

On 2026/2/20 06:05, kernel test robot wrote:
> Hi Leon,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on bpf-next/master]
>
> url: https://github.com/intel-lab-lkp/linux/commits/Leon-Hwang/bpf-Introduce-64-bit-bitops-kfuncs/20260219-223550
> base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> patch link: https://lore.kernel.org/r/20260219142933.13904-3-leon.hwang%40linux.dev
> patch subject: [PATCH bpf-next v2 2/6] bpf, x86: Add 64-bit bitops kfuncs support for x86_64
> config: x86_64-randconfig-073-20260220 (https://download.01.org/0day-ci/archive/20260220/202602200536.JWzGHAc6-lkp@xxxxxxxxx/config)

Ack.

It was caused by the missing CONFIG_BPF_SYSCALL.

$ rg _BPF .config
118:CONFIG_BPF=y
120:CONFIG_ARCH_WANT_DEFAULT_BPF_JIT=y
125:# CONFIG_BPF_SYSCALL is not set
126:CONFIG_BPF_JIT=y
127:CONFIG_BPF_JIT_DEFAULT_ON=y
1339:CONFIG_LWTUNNEL_BPF=y
7449:CONFIG_IO_URING_BPF=y

I'll make those symbols relied on CONFIG_BPF_SYSCALL in the next revision.

Thanks,
Leon

> compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260220/202602200536.JWzGHAc6-lkp@xxxxxxxxx/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202602200536.JWzGHAc6-lkp@xxxxxxxxx/
>
> All errors (new ones prefixed by >>):
>
> ld: arch/x86/net/bpf_jit_comp.o: in function `bpf_inlines_func_call':
>>> arch/x86/net/bpf_jit_comp.c:1621:(.text+0xe70b): undefined reference to `bpf_clz64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1647:(.text+0xe718): undefined reference to `bpf_ctz64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1673:(.text+0xe725): undefined reference to `bpf_ffs64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1677:(.text+0xe732): undefined reference to `bpf_fls64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1683:(.text+0xe743): undefined reference to `bpf_popcnt64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1707:(.text+0xe758): undefined reference to `bpf_rol64'
>>> ld: arch/x86/net/bpf_jit_comp.c:1714:(.text+0xe765): undefined reference to `bpf_ror64'
> ld: arch/x86/net/bpf_jit_comp.c:1647:(.text+0x10e85): undefined reference to `bpf_ctz64'
> ld: arch/x86/net/bpf_jit_comp.c:1673:(.text+0x10e92): undefined reference to `bpf_ffs64'
> ld: arch/x86/net/bpf_jit_comp.o: in function `bpf_jit_inlines_kfunc_call':
>>> arch/x86/net/bpf_jit_comp.c:4247:(.text+0x177c8): undefined reference to `bpf_ffs64'
> ld: arch/x86/net/bpf_jit_comp.c:4247:(.text+0x177d1): undefined reference to `bpf_ctz64'
> ld: arch/x86/net/bpf_jit_comp.c:4250:(.text+0x177da): undefined reference to `bpf_fls64'
>>> ld: arch/x86/net/bpf_jit_comp.c:4250:(.text+0x177e3): undefined reference to `bpf_clz64'
> ld: arch/x86/net/bpf_jit_comp.c:4253:(.text+0x177ec): undefined reference to `bpf_popcnt64'
> ld: arch/x86/net/bpf_jit_comp.c:4256:(.text+0x177f5): undefined reference to `bpf_ror64'
> ld: arch/x86/net/bpf_jit_comp.c:4256:(.text+0x177ff): undefined reference to `bpf_rol64'
>
>
> vim +1621 arch/x86/net/bpf_jit_comp.c
>
> 1607
> 1608 static bool bpf_inlines_func_call(u8 **pprog, void *func)
> 1609 {
> 1610 bool has_popcnt = boot_cpu_has(X86_FEATURE_POPCNT);
> 1611 bool has_bmi1 = boot_cpu_has(X86_FEATURE_BMI1);
> 1612 bool has_abm = boot_cpu_has(X86_FEATURE_ABM);
> 1613 bool inlined = true;
> 1614 u8 *prog = *pprog;
> 1615
> 1616 /*
> 1617 * x86 Bit manipulation instruction set
> 1618 * https://en.wikipedia.org/wiki/X86_Bit_manipulation_instruction_set
> 1619 */
> 1620
>> 1621 if (func == bpf_clz64 && has_abm) {
> 1622 /*
> 1623 * Intel® 64 and IA-32 Architectures Software Developer's Manual (June 2023)
> 1624 *
> 1625 * LZCNT - Count the Number of Leading Zero Bits
> 1626 *
> 1627 * Opcode/Instruction
> 1628 * F3 REX.W 0F BD /r
> 1629 * LZCNT r64, r/m64
> 1630 *
> 1631 * Op/En
> 1632 * RVM
> 1633 *
> 1634 * 64/32-bit Mode
> 1635 * V/N.E.
> 1636 *
> 1637 * CPUID Feature Flag
> 1638 * LZCNT
> 1639 *
> 1640 * Description
> 1641 * Count the number of leading zero bits in r/m64, return
> 1642 * result in r64.
> 1643 */
> 1644 /* emit: x ? 64 - fls64(x) : 64 */
> 1645 /* lzcnt rax, rdi */
> 1646 EMIT5(0xF3, 0x48, 0x0F, 0xBD, 0xC7);
>> 1647 } else if (func == bpf_ctz64 && has_bmi1) {
> 1648 /*
> 1649 * Intel® 64 and IA-32 Architectures Software Developer's Manual (June 2023)
> 1650 *
> 1651 * TZCNT - Count the Number of Trailing Zero Bits
> 1652 *
> 1653 * Opcode/Instruction
> 1654 * F3 REX.W 0F BC /r
> 1655 * TZCNT r64, r/m64
> 1656 *
> 1657 * Op/En
> 1658 * RVM
> 1659 *
> 1660 * 64/32-bit Mode
> 1661 * V/N.E.
> 1662 *
> 1663 * CPUID Feature Flag
> 1664 * BMI1
> 1665 *
> 1666 * Description
> 1667 * Count the number of trailing zero bits in r/m64, return
> 1668 * result in r64.
> 1669 */
> 1670 /* emit: x ? __ffs64(x) : 64 */
> 1671 /* tzcnt rax, rdi */
> 1672 EMIT5(0xF3, 0x48, 0x0F, 0xBC, 0xC7);
>> 1673 } else if (func == bpf_ffs64 && has_bmi1) {
> 1674 /* emit: __ffs64(x); x == 0 has been handled in verifier */
> 1675 /* tzcnt rax, rdi */
> 1676 EMIT5(0xF3, 0x48, 0x0F, 0xBC, 0xC7);
>> 1677 } else if (func == bpf_fls64 && has_abm) {
> 1678 /* emit: fls64(x) */
> 1679 /* lzcnt rax, rdi */
> 1680 EMIT5(0xF3, 0x48, 0x0F, 0xBD, 0xC7);
> 1681 EMIT3(0x48, 0xF7, 0xD8); /* neg rax */
> 1682 EMIT4(0x48, 0x83, 0xC0, 0x40); /* add rax, 64 */
>> 1683 } else if (func == bpf_popcnt64 && has_popcnt) {
> 1684 /*
> 1685 * Intel® 64 and IA-32 Architectures Software Developer's Manual (June 2023)
> 1686 *
> 1687 * POPCNT - Return the Count of Number of Bits Set to 1
> 1688 *
> 1689 * Opcode/Instruction
> 1690 * F3 REX.W 0F B8 /r
> 1691 * POPCNT r64, r/m64
> 1692 *
> 1693 * Op/En
> 1694 * RM
> 1695 *
> 1696 * 64 Mode
> 1697 * Valid
> 1698 *
> 1699 * Compat/Leg Mode
> 1700 * N.E.
> 1701 *
> 1702 * Description
> 1703 * POPCNT on r/m64
> 1704 */
> 1705 /* popcnt rax, rdi */
> 1706 EMIT5(0xF3, 0x48, 0x0F, 0xB8, 0xC7);
>> 1707 } else if (func == bpf_rol64) {
> 1708 EMIT1(0x51); /* push rcx */
> 1709 /* emit: rol64(x, s) */
> 1710 EMIT3(0x48, 0x89, 0xF1); /* mov rcx, rsi */
> 1711 EMIT3(0x48, 0x89, 0xF8); /* mov rax, rdi */
> 1712 EMIT3(0x48, 0xD3, 0xC0); /* rol rax, cl */
> 1713 EMIT1(0x59); /* pop rcx */
>> 1714 } else if (func == bpf_ror64) {
> 1715 EMIT1(0x51); /* push rcx */
> 1716 /* emit: ror64(x, s) */
> 1717 EMIT3(0x48, 0x89, 0xF1); /* mov rcx, rsi */
> 1718 EMIT3(0x48, 0x89, 0xF8); /* mov rax, rdi */
> 1719 EMIT3(0x48, 0xD3, 0xC8); /* ror rax, cl */
> 1720 EMIT1(0x59); /* pop rcx */
> 1721 } else {
> 1722 inlined = false;
> 1723 }
> 1724
> 1725 *pprog = prog;
> 1726 return inlined;
> 1727 }
> 1728
>