From:	Keith Owens <kaos@ocs.com.au>
To:	linux-kernel@vger.rutgers.edu
Subject: Announce: modutils 2.3.11 is available - the debugger's helper
Date:	Fri, 21 Apr 2000 22:24:35 +1000

Fastest download from kernel.org.
Mirror at ftp://ftp.**.kernel.org/pub/linux/utils/kernel/modutils/v2.3
           replace '**' with your favourite local kernel.org mirror.
Mirror at ftp://oss.sgi.com/pub/mirror/modutils/v2.3.
Master at ftp://ftp.ocs.com.au/pub/modutils/v2.3.  (slow)

patch-modutils-2.3.11.gz        Patch from modutils 2.3.10 to 2.3.11
modutils-2.3.11.tar.gz          Source tarball, includes RPM spec file
modutils-2.3.11-1.src.rpm       As above, in SRPM format
modutils-2.3.11-1.i386.rpm      Compiled with egcs-2.91.66, glibc 2.1.2

Changelog extract

	* Add ieee1394 directory, requested by Andreas Bombe.
	* Documentation and options updates.  Add long options, clean
	  up missing or incorrect usage entries.  Callum <no last name>.
	* White space cleanup.
	* Do meta expansion on "include" and "if" parameters.
	* Ignore genksyms suffix when reading map from -F.
	* Add support for kallsyms to assist kernel debugging.
	* Hint message for -EBUSY.
	* Sanity check on number of local symbols.

The meta expansion on "include" and "if" parameters means that you can
include the kernel version (`uname -r` or `kernelversion`) in tests for
filenames, "if -f /lib/modules/`uname -r`/ide/ide-probe.o".

The "Add support for kallsyms to assist kernel debugging" change is the
interesting one.  If your kernel is compiled with CONFIG_KALLSYMS[1]
then the kernel and all loaded modules automatically contain a complete
list of all non-stack kernel symbols.  No longer does each debugger
have to hunt around for symbols or include its own code to handle
symbol tables as modules are loaded or unloaded, it is now a standard
feature[1].

Loading a complete non-stack symbol table is relatively expensive, it
adds 10-20% to the size of the kernel and modules.  The CONFIG_KALLSYMS
option should only be used when debugging.  The kallsyms data contains
a lot of data, for the kernel and for each module it lists

* The section names, start and end addresses.
* The symbol names, start and end addresses and the section each symbol
  belongs to.

Why this much data?  Because if you have the start address of the
section and the start and end of a symbol, you can get a clean
disassemble of a module with addresses that match your system by

  objdump -S -j <section_name> --adjust-vma=<section_start> \
  	--start-address=<symbol_start> --stop-address=<symbol_end> \
	module.o

A similar command for the kernel, omit --adjust-vma because the kernel
is executable, not relocatable.

  objdump -S -j <section_name> \
  	--start-address=<symbol_start> --stop-address=<symbol_end> \
	vmlinux

-S disassembles the section.  If you compiled the kernel with -g you
even get source and binary interleaved in the objdump listing.

As proof of concept, modutils/v2.3/patch-2.2.15pre19-kallsyms-kdb-v0.6.gz
is the SGI kdb patch for 2.2 kernels reworked to use kallsyms.

* It uses kallsyms for its symbol table instead of the SGI symbol
  table.
* No fixed size for the symbol table and no need to ask the user for a
  size at compile time.
* Using the section data accurately verifies that an address falls
  within a kernel or module section instead of using the less reliable
  test on _[se]text and vmalloc areas.
* Every symbol printed is followed by the module name, the section
  start, the symbol start and end addresses.  Feed these addresses into
  objdump -S for a nice disassemble.

[1] CONFIG_KALLSYMS support is not currently integrated into the
    kernel.  See patch*kallsyms* in modutils/v2.3 for patches against
    2.2.15pre19 for kallsyms alone and for kallsyms+kdb.  Versions for
    other kernels and SGI kdb to follow.


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