jm + gdb   7

poor man's profiler
'Sampling tools like oprofile or dtrace's profile provider don't really provide methods to see what [multithreaded] programs are blocking on - only where they spend CPU time. Though there exist advanced techniques (such as systemtap and dtrace call level probes), it is overkill to build upon that. Poor man doesn't have time. Poor man needs food.'

Basically periodically grabbing stack traces from running processes using gdb.
gdb  profiling  linux  unix  mark-callaghan  stack-traces  performance 
11 days ago by jm
8 gdb tricks you should know (Ksplice Blog)
These are very good -- bookmarking for the next time I'm using gdb, probably about 3 years from now
c  debugging  gdb  c++  tips  coding 
january 2015 by jm
rr
A cool-looking new debugging tool for C/C++ from Mozilla.
Many, many people have noticed that if we had a way to reliably record program execution and replay it later, with the ability to debug the replay, we could largely tame the nondeterminism problem. This would also allow us to deliberately introduce nondeterminism so tests can explore more of the possible execution space, without impacting debuggability. Many record and replay systems have been built in pursuit of this vision. (I built one myself.) For various reasons these systems have not seen wide adoption. So, a few years ago we at Mozilla started a project to create a new record-and-replay tool that would overcome the obstacles blocking adoption. We call this tool rr.


Low runtime overhead; easy deployability; targeted at 32-bit (?!) Linux; OSS. (via Bryan O'Sullivan)
via:bos  mozilla  debugging  coding  firefox  rr  record  replay  gdb  c++  linux 
march 2014 by jm
dumping a JVM heap using gdb
now this is a neat trick -- having been stuck having to flip to spares and do other antics while a long-running heap dump took place, this is a winner.
Dumping a JVM’s heap is an extremely useful tool for debugging problems with a J2EE application. Unfortunately, when a JVM explodes, using the standard jmap tool can take an inordinate amount of time to execute for lots of different reasons. This leads to extended downtime when a heap dump is attempted and even then, jmap regularly fails.
This blog post is intended to outline an alternate method using [gdb] to achieve a heap dump that only requires mere seconds of additional downtime allowing the slow jmap process to happen once the application is back in service.
heap-dump  gdb  heap  jvm  java  via:peakscale  gcore  core  core-dump  debugging 
march 2013 by jm
Peek and poke in the age of Linux
Neat demo of using ptrace to inject into a running process, just like the good old days ;)
Some time ago I ran into a production issue where the init process (upstart) stopped behaving properly. Specifically, instead of spawning new processes, it deadlocked in a transitional state. [...] What’s worse, upstart doesn’t allow forcing a state transition and trying to manually create and send DBus events didn’t help either. That meant the sane options we were left with were:
restart the host (not desirable at all in that scenario);
start the process manually and hope auto-respawn will not be needed.
Of course there are also some insane options. Why not cheat like in the old times and just PEEK and POKE the process in the right places? The solution used at the time involved a very ugly script driving gdb which probably summoned satan in some edge cases. But edge cases were not hit and majority of hosts recovered without issues.
debugging  memory  linux  upstart  peek  poke  ptrace  gdb  processes  hacks 
march 2013 by jm
gist: 782263 - How to redirect a running process' output to a file and logout
a nifty gdb hack; essentially dup()s a couple of files in /tmp in place of fd 1 and 2, then uses the bashism "detach" to nohup the running process
gdb  hacks  linux  process  shell  unix  via:hn  nifty  dup  detach  bash  from delicious
january 2011 by jm
Hijack: Get A Live IRB Prompt For Any Existing Ruby Process
injects via gdb. pretty cool, if it works; one comment notes that they couldn't use it on a Rails app
gdb  hijack  ruby  debugging  irb  live  coding  rubygems  debugger 
august 2009 by jm

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