On Mon, 25 Sep 2006, Vivek Goyal wrote:
One thing I like *very much* in gdb is its ability to display function
params and local variables in any stack frame, and I haven't found out how
to do it with crash.
Agreed. AFAIK, crash does not display the function params and local
variables. gdb has got this advantage, though last time I looked
at local variables dispalyed by gdb, they seemed to be junk. Not very
sure why it was so?
Most probably this is due to compiler optimizations, eg. the register is
reused for another purpose. Recently I was pleased to discover that gdb
6.5 is smart enough to tell the user that a variable has been optimized
out (certainly with help from debug info produced by gcc).
I agree that gdb is sometimes very slow, but maybe it's easier to
optimize gdb than to make crash smarter?
I beg to differ here. Not sure why it is easier to optimize gdb. If we
try to optimize gdb by writing scripts, then IMHO, writing C program is
easier and faster. If the idea is to optimize gdb by modifying gdb code
then its no different than crash. In fact, why to reinvent the wheel if
crash already does so many things for us. Yes, but probably we need to
modify crash to be able to obtain function parameters and local
variables.
Oh I only meant that *maybe* gdb deserved some optimizations that would be
suitable for general use, but this is pure speculation. I agree that a
custom modified gdb is in a way akin to crash.
For this particular problem (listing threads), the real fix would be to
add the PT_NOTE entry that each thread deserves, then gdb would let you
do "info threads" instead, and dump nice backtraces of each.
Displaying even the currently non executing threads using "info threads"
and their backtraces is interesting. Crash can already do that. I am
apprehensive about traversing through the task list and dumping every
thread's register state after a crash. There is no gurantee that list is
in a sane state. And in general, we are trying to make crash handler as
small as possible to improve the reliability of dumping operation.
Register state of every non-executing thread is already present in the
vmcore and IMHO, we should write scripts to get info about other
threads then doing it in kernel.
This is exactly what I had in mind, for the very reasons you mentioned.
:-)
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