1. Washington University
Smart Port Card
Tutorial
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SPC Utilities
Edward Spitznagel
Washington University

2. Utilities - Overview Purpose of SPC Utilities:
glue between various software components
simplify other parts of the system
solve miscellaneous problems encountered
There aren’t as many as there used to be.
Utilities that are still useful:
mkimg - make image
mknl - make namelist

3. mkimg - overview
Creates a kernel image suitable for downloading to the SPC
Removes some of the burden from the bootloader

4. Kernel Image
On Disk:
This is what the NetBSD kernel in a.out format looks like on the disk
e.g. the file /netbsd on most systems
exec header
text segment
initialized data
symbol table
(optional)
string table
(optional)

5. Kernel Image
On Disk:
(e.g. the file /netbsd)
In Memory:
(as loaded by bootloader)
This is what the kernel image looks like when loaded into memory.
What’s different?
BSS segment has been inserted in the middle.
exec header
exec header
text segment
text segment
initialized data
initialized data
symbol table
(optional)
BSS segment
(uninitialized data)
string table
(optional)
symbol table
(optional)
string table
(optional)

6. mkimg - summary Kernel requires BSS segment for execution.
Normal PC: done at boot time (by the bootloader)
SPC: done by mkimg, after kernel build
mkimg creates a copy of the kernel file with the BSS segment included.
mkimg is invoked by “make” from the mk.3 script

7. mknl - purpose Certain system tools need a kernel namelist:
ps, netstat, top, uptime, etc.
Normally, this is read from kernel file (/netbsd)
Problem: kernel too large to fit on filesystem
Solution:
create a file that we can put on the filesystem, to hold the namelist information
file should look as much like the real kernel as possible

8. Kernel Image mknl utility: input: kernel in a.out format
On Disk:
(e.g. the file /netbsd)
mknl utility:
input: kernel in a.out format
output: the “symbols only” file
approach:
open input and output files
copy exec header
lseek past text and data segments
copy symbol table and string table
close files
exec header
text segment
initialized data
symbol table
(optional)
string table
(optional)

9. a file with a hole mknl creates a file with a hole
unneeded blocks are not allocated
Example of a file with a hole:
block array for the file:
disk block
disk block
null
null
null
null
disk block
disk block
. . .

10. 152 -rw-r--r-- 1 root wheel 24624114 /netbsd
output from mknl
Output file
from mknl:
This is what the symbols-only netbsd file looks like
This is what we put into our filesystem as /netbsd
Doesn’t require much space
typically around 150kB
Example: from a 24MB kernel:
exec header
hole
(used to be
text segment)
hole
(used to be
initialized data)
152 -rw-r--r-- 1 root wheel /netbsd
symbol table
string table

11. mknl - implications Implication of a files with holes:
Copying can produce undesirable results: holes look like blocks full of zeroes...
new file will be as large as the original kernel
defeats purpose of mknl
Need to mknl directly into the filesystem.
Need to mknl after any changes are made to the kernel.
mknl is invoked by mk.2 script

12. Conclusion Utilities The End
mkimg - make a kernel image suitable for downloading to SPC
mknl - makes a “symbols-only” file to reside on the SPC filesystem
The End