This section provides some examples of setting event handlers.
This example shows how to set a data change breakpoint on array[99]:
(dbx) stop access w &array[99] (2) stop access w &array[99], 4 (dbx) run Running: watch.x2 watchpoint array[99] (0x2ca88[4]) at line 22 in file "watch.c" 22 array[i] = i;
This example shows how to implement a simple trace:
(dbx) when step { echo at line $lineno; }
The following example shows how to enable a handler while within a function:
<dbx> trace step -in foo
This command is equivalent to the following:
# create handler in disabled state when step -disable { echo Stepped to $line; } t=$newhandlerid # remember handler id when in foo { # when entered foo enable the trace handler -enable "$t" # arrange so that upon returning from foo, # the trace is disabled. when returns { handler -disable "$t"; }; }
This example shows how to see how many lines have been executed in a small program, type:
(dbx) stop step -count infinity # step and stop when count=inf (2) stop step -count 0/infinity (dbx) run ... (dbx) status (2) stop step -count 133/infinity
The program never stops, and then the program terminates. The number of lines executed is 133. This process is very slow. It is most useful with breakpoints on functions that are called many times.
This example shows how to count how many instructions a line of code executes:
(dbx) ... # get to the line in question (dbx) stop step -instr -count infinity (dbx) step ... (dbx) status (3) stop step -count 48/infinity # 48 instructions were executed
If the line you are stepping over makes a function call, the lines in the function are counted as well. You can use the next event instead of step to count instructions, excluding called functions.
Enable a breakpoint only after another event has occurred. For example, you would use the following breakpoint if your program begins to execute incorrectly in function hash, but only after the 1300th symbol lookup.
(dbx) when in lookup -count 1300 { stop in hash hash_bpt=$newhandlerid when proc_gone -temp { delete $hash_bpt; } }
In this example, if your application processes files that need to be reset during a replay, you can write a handler to do that each time you run the program.
(dbx) when sync { sh regen ./database; } (dbx) run < ./database... # during which database gets clobbered (dbx) save ... # implies a RUN, which implies the SYNC event which (dbx) restore # causes regen to run
This example shows how to see quickly where the program is while it is running, type:
(dbx) ignore sigint (dbx) when sig sigint { where; cancel; }
You would then issue ^C to see a stack trace of the program without stopping it.
This example is basically what the collector hand sample mode does (and more). Use SIGQUIT (^\) to interrupt the program because ^C is now used.
The following example shows how to catch only specific floating-point exceptions, for example, IEEE underflow:
(dbx) ignore FPE # disable default handler (dbx) help signals | grep FPE # can’t remember the subcode name ... (dbx) stop sig fpe FPE_FLTUND ...
For more information about enabling ieee handlers, see Trapping the FPE Signal (Oracle Solaris Only).