Andrew,
A few pieces of information... you probably already know most of this...
* Debugging -g -O code has it's limitations, I assume that is
understood. Sometimes local variable information is not included,
sometimes the source line to instruction mapping is a bit hectic
or missing. It can be very valuable at times, just strange.
* Using javac -g will just add information about local variables,
source line information is always there by default.
And you can't easily 'strip' debug information from class files that I
am aware of. I'm a bit puzzled how you can remove the debug
information from the classfiles and put that in a separate package.
* It has been my experience that the resulting gcc object code (machine
instructions in the .text and data in the .data sections) from
building with and without -g can be different.
An a.out built with 'cc -g -O' and then stripped, is not the same
thing as an a.out built with just 'cc -O' in all cases.
Or at least that has been my experience.
If people are willing to accept any loss of optimization that
'-g -O' might cause, that is fine, just making the observation.
* A "debug" build sometimes means that the native code includes
the assert() coding, valuable runtime checking, but potentially
a major performance problem and does increase the code size.
Did you mean to include assert() code? I assume not.
Our JDK "fastdebug" builds are built with -g -O and include the
assert checking code, so it's a bit of a compromise debug build
runs reasonably fast, can be debugged to some degree, asserts
can catch problems at runtime, etc.
Having said those things, I have always been a supporter of the -g
option just adding information to a .o or binary and not letting the
desire to debug a program influence the optimizations you asked for.
And an ability to just carry the debug information in a sidecar like
package is a great concept.
So if you come up with some kind of setting for this, I would support
adding it, just not sure you will get exactly what you want at first,
may need to play with it.
-kto
Andrew Haley wrote:
In GNU/Linux/BSD/etc systems we normally want to be able to debug
installed packages. So, in many distributions there is a rule that
all packages must be built with full debug information. This isn't
quite as bloated as it might sound, as we extract all such debug
information files and put it into separate debug packages. So, when
someone has a problem that we need to debug we can download the debug
package to their computer and attach a debugger without needing to
recompile anything.
As far as I've been able to determine there is no simple way to turn
on debug information in OpenJDK builds. So, in IcedTea we have a
number of patches that turn on debugging in various makefiles and
build.xml files, but of course we miss things. I recently tried to
debug javac but discovered that it wasn't possible because it hadn't
been compiled with full debug info:
<javac srcdir="${src.classes}" destdir="${build.bootclasses}"
source="${compiler.source.level}" debug="true"
debuglevel="source,lines"
Note that there's no way to override the debuglevel without editing
build.xml.
I think we need a single overriding option when building OpenJDK that
enables debug information everywhere, no matter what the build target.
Note that I'm not talking here about any of OpenJDK's internal
debugging aids, just the -g options passed to javac and the various C
and C++ compilers.
While I could write this as an IcedTea patch, I believe that it's
something that should go into OpenJDK proper. Would that be
acceptable?
Thanks,
Andrew.
