kdb是否支持ARM64硬件断点？使用bph触发内核空指针解引用

与gdb不同，KDB的手册和参考资料十分稀少，可查资料包括：

• kdb(8) 手册页
• ELinux上的KDB相关文档
• 内核官方文档中的kgdb工具说明

在Linux 6.1版本的ARM64开发板上尝试使用bph（硬件断点）命令设置断点时，触发了kernel NULL pointer dereference at virtual address 0000000000000000错误，具体日志如下：

root@root:~# echo g > /proc/sysrq-trigger
[ 2189.865491] sysrq: DEBUG

进入kdb（当前进程=0xffff0003856b5700，PID 314），触发原因：键盘输入（SysRq）
[4]kdb> bph jiffies_read
指令(寄存器)断点 #0 位于 0xffff800008135ee0（jiffies_read）
    已启用   地址为 ffff800008135ee0，硬件类型=1 已安装=0

[4]kdb> go
[ 2220.051476] 无法处理内核空指针解引用，虚拟地址 0000000000000000
[ 2220.051719] 内存中止信息：
[ 2220.051750]   ESR = 0x0000000086000005
[ 2220.051841]   EC = 0x21: IABT（当前异常级别），IL = 32位
[ 2220.051898]   SET = 0，FnV = 0
[ 2220.051934]   EA = 0，S1PTW = 0
[ 2220.051977]   FSC = 0x05：一级页表转换错误
[ 2220.052195] 用户页表：64k页面，48位虚拟地址，pgdp=0000000402e23a00
[ 2220.052254] [0000000000000000] pgd=0000000000000000，p4d=0000000000000000，pud=0000000000000000
[ 2220.052804] 内部错误：Oops: 0000000086000005 [#1] PREEMPT_RT SMP
[ 2220.054226] 已加载模块：无
[ 2220.054509] CPU: 4 PID: 314 进程名: bash 内核未污染 6.1.12-rt7
[ 2220.054566] 硬件名称: ARM64 board
[ 2220.054595] pstate: 004003c9 (nzcv DAIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 2220.054638] pc : 0x0
[ 2220.054811] lr : kdb_bp_install+0x120/0x200
[ 2220.054865] sp : ffff80000a46f870
[ 2220.054879] x29: ffff80000a46f870 x28: ffff8000090b8000 x27: ffff8000090bb1c0
[ 2220.054939] x26: ffff80000a46fb30 x25: ffff8000088dd610 x24: ffff8000088dd5d8
[ 2220.054988] x23: ffff8000090b8ff4 x22: ffff8000090b8cd8 x21: ffff8000090bb1c0
[ 2220.055037] x20: 0000000000000000 x19: 0000000000000000 x18: 0000000000000001
[ 2220.055084] x17: 0000000000000000 x16: 0000000000000000 x15: ffff0003856b5bd0
[ 2220.055131] x14: 0000000000000000 x13: 0000000000000000 x12: ffff8000090b9000
[ 2220.055178] x11: 0000000000000022 x10: ffffffffff9836a8 x9 : 0000000000000010
[ 2220.055226] x8 : 0101010101010101 x7 : 7f7f7f7f7f7f7f7f x6 : 0000000000220400
[ 2220.055274] x5 : 0000000000000000 x4 : ffff8003f6d10000 x3 : 0000000000000000
[ 2220.055320] x2 : 0000000000000001 x1 : 0000000000000001 x0 : ffff800008135ee0
[ 2220.055371] 调用栈：
[ 2220.055392]  0x0
[ 2220.055423]  kdb_stub+0x288/0x428
[ 2220.055455]  kgdb_cpu_enter+0x168/0x740
[ 2220.055493]  kgdb_handle_exception+0xd0/0x128
[ 2220.055531]  kgdb_compiled_brk_fn+0x28/0x38
[ 2220.055567]  call_break_hook+0x6c/0x80
[ 2220.055597]  brk_handler+0x1c/0x60
[ 2220.055623]  do_debug_exception+0x8c/0x118
[ 2220.055655]  el1_dbg+0x38/0x58
[ 2220.055690]  el1h_64_sync_handler+0xc8/0xe8
[ 2220.055718]  el1h_64_sync+0x64/0x68
[ 2220.055741]  kgdb_breakpoint+0x1c/0x80
[ 2220.055773]  __handle_sysrq+0x90/0x1a0
[ 2220.055821]  write_sysrq_trigger+0x74/0x98
[ 2220.055855]  proc_reg_write+0xa4/0xf8
[ 2220.055894]  vfs_write+0xd0/0x388
[ 2220.055934]  ksys_write+0x6c/0x100
[ 2220.055968]  __arm64_sys_write+0x1c/0x28
[ 2220.056007]  invoke_syscall+0x44/0x108
[ 2220.056061]  el0_svc_common.constprop.0+0x44/0xf0
[ 2220.056109]  do_el0_svc+0x2c/0xc8
[ 2220.056150]  el0_svc+0x28/0x98
[ 2220.056174]  el0t_64_sync_handler+0xb8/0xc0
[ 2220.056200]  el0t_64_sync+0x18c/0x190
[ 2220.056592] 代码：无效PC值
[ 2220.083989] ---[ 跟踪结束 0000000000000000 ]---
[ 2220.084622] 内核崩溃 - 无法同步：Oops: 致命异常

内容的提问来源于stack exchange，提问作者alex zhang