kern/54322: strange kdump output

[martin%NetBSD.org@localhost]

>Number:         54322
>Category:       kern
>Synopsis:       strange kdump output
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 24 09:15:00 +0000 2019
>Originator:     Martin Husemann
>Release:        NetBSD 8.99.47
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD martins.aprisoft.de 8.99.47 NetBSD 8.99.47 (GENERIC) #0: Fri Jun 21 16:57:12 UTC 2019 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:

While ktracing a threaded application I noticed strange output in kdump:

  6851      1 gxemul   CALL  read(4,0x7d05e3f9e000,0x1000)
  6851      1 gxemul   GIO   fd 4 read 4088 bytes
[... data content stripped ...]
  6851      1 gxemul   GIO   fd 4 read 8 bytes
       "%\M^@\M^@\0\^D\0@\^P"
  6851      1 gxemul   RET   read 4096/0x1000

I expected a request of 0x1000 to just trigger the transfer of upto
4096/0x1000 bytes. Why is GIO accounting for additional stuff?

>How-To-Repeat:
Not sure, seems to be reproducable for me.

>Fix:
n/a