Regions start identifier is missing when printing verbose element output with backtrace metadata

[fidgetingbits]

The following example is from me printing the contents of a cache using --show-region -v -M backtrace. Note that the entry 0xffff8881039ec000 would normally be marked as (region start), which is missing in this output. It may be something we want to re-add.

  struct kmem_cache_cpu @ 0xffff88813bc36120 (cpu 0) {
    freelist = 0xffff8881039ecb00 (2 elements)
    page     = struct page @ 0xffffea00040e7b00 {
      objects  = 32
      inuse    = 21 (real = 19)
      frozen   = 1
      freelist = 0xffff8881039ed200 (11 elements)
      region   @ 0xffff8881039ec000-0xffff8881039ee000 (32 elements)
        0xffff8881039ec000 M
        #0  0xffffffff8133a6e1 in kmem_cache_free (s=0xffff8881001f2700, x=0xffff88810a02b300) at /build/linux-HMZHpV/linux-5.15.0
/mm/slub.c:3509
#1  0xffffffff81a819ee in kfree_skbmem (skb=skb@entry=0xffff88810a02b300) at /build/linux-HMZHpV/linux-5.15.0/net/core/skbuff.c:70
0
#2  0xffffffff81a85243 in __kfree_skb (skb=0xffff88810a02b300) at /build/linux-HMZHpV/linux-5.15.0/net/core/skbuff.c:757
#3  consume_skb (skb=0xffff88810a02b300) at /build/linux-HMZHpV/linux-5.15.0/net/core/skbuff.c:912
#4  consume_skb (skb=0xffff88810a02b300) at /build/linux-HMZHpV/linux-5.15.0/net/core/skbuff.c:906
#5  0xffffffff81a8b506 in skb_free_datagram (sk=sk@entry=0xffff888109038000, skb=<optimized out>) at /build/linux-HMZHpV/linux-5.1
5.0/net/core/datagram.c:325
#6  0xffffffff81beaa54 in __unix_dgram_recvmsg (sk=0xffff888109038000, msg=<optimized out>, size=<optimized out>, flags=<optimized
 out>) at /build/linux-HMZHpV/linux-5.15.0/net/unix/af_unix.c:2383
#7  0xffffffff81bead46 in unix_dgram_recvmsg (sock=<optimized out>, msg=<optimized out>, size=<optimized out>, flags=<optimized ou
t>) at /build/linux-HMZHpV/linux-5.15.0/net/unix/af_unix.c:2401
#8  0xffffffff81a743a0 in sock_recvmsg_nosec (flags=64, msg=0xffffc90000c67e40, sock=0xffff8881032f9d40) at /build/linux-HMZHpV/li
nux-5.15.0/net/socket.c:947
#9  sock_recvmsg (sock=sock@entry=0xffff8881032f9d40, msg=msg@entry=0xffffc90000c67e40, flags=flags@entry=64) at /build/linux-HMZH
pV/linux-5.15.0/net/socket.c:965
#10 0xffffffff81a74578 in ____sys_recvmsg (sock=sock@entry=0xffff8881032f9d40, msg_sys=msg_sys@entry=0xffffc90000c67e40, msg=msg@e
ntry=0x7f9630ae6260, uaddr=0x0 <fixed_percpu_data>, flags=<optimized out>, flags@entry=64, nosec=nosec@entry=0) at /build/linux-HM
ZHpV/linux-5.15.0/net/socket.c:2631
#11 0xffffffff81a7708c in ___sys_recvmsg (sock=sock@entry=0xffff8881032f9d40, msg=msg@entry=0x7f9630ae6260, msg_sys=msg_sys@entry=
0xffffc90000c67e40, flags=flags@entry=64, nosec=nosec@entry=0) at /build/linux-HMZHpV/linux-5.15.0/net/socket.c:2673
#12 0xffffffff81a77cef in __sys_recvmsg (fd=<optimized out>, msg=0x7f9630ae6260, flags=64, forbid_cmsg_compat=forbid_cmsg_compat@e
ntry=true) at /build/linux-HMZHpV/linux-5.15.0/net/socket.c:2703
#13 0xffffffff81a77d5d in __do_sys_recvmsg (flags=<optimized out>, msg=<optimized out>, fd=<optimized out>) at /build/linux-HMZHpV
/linux-5.15.0/net/socket.c:2713
#14 __se_sys_recvmsg (flags=<optimized out>, msg=<optimized out>, fd=<optimized out>) at /build/linux-HMZHpV/linux-5.15.0/net/sock
et.c:2710
#15 __x64_sys_recvmsg (regs=<optimized out>) at /build/linux-HMZHpV/linux-5.15.0/net/socket.c:2710
#16 0xffffffff81d4521c in do_syscall_x64 (nr=<optimized out>, regs=0xffffc90000c67f58) at /build/linux-HMZHpV/linux-5.15.0/arch/x8
6/entry/common.c:50
#17 do_syscall_64 (regs=0xffffc90000c67f58, nr=<optimized out>) at /build/linux-HMZHpV/linux-5.15.0/arch/x86/entry/common.c:80
#18 0xffffffff81e0007c in entry_SYSCALL_64 () at /build/linux-HMZHpV/linux-5.15.0/arch/x86/entry/entry_64.S:113
#19 0x00007f962c000bb0 in ?? ()
Backtrace stopped: Cannot access memory at address 0x1000
        --
        0xffff8881039ec100 F
        chunk address not found in metadata database
        --