so I know that my current block is between epb and esp
is there a way to print my stack the following way:
lets says that len=ebp-esp
I would like a command on gdb that would look like this
x/lenx $esp
so I'm priting what's on the stack for the current function being executed?
can I do this using display like:
display/lenx $esp ?
is it possible to have a variable that will change each time
Seems display doesn't allow this. So you can define your own command and simply call it when you need to see a function stack:
define display_stack
eval "x /%dbx $esp", $ebp-$esp
end
And then while debugging your program:
(gdb) display_stack
If you need to see your function stack on each step you can 1) define another command nn and use it when you debug your functions 2) use hook for the pseudo-command, ‘stop’ :
define nn
n
display_stack
end
define hook-stop
echo "hook-stop, display_stack:\n"
display_stack
end
Useful links:
http://sourceware.org/gdb/onlinedocs/gdb/Define.html
http://sourceware.org/gdb/onlinedocs/gdb/Output.html#index-eval-1736
http://sourceware.org/gdb/onlinedocs/gdb/Hooks.html
Related
GDB allows registering a set of commands to a specific breakpoint via commands NUM syntax. I need to register the set of commands for a specific breakpoint via an external file, by using a syntax something like the following:
commands ./main.c:18
silent
print buffer[0]
cont
end
commands ./io.c:29
silent
printf "Hello world %i\n", myvar1
cont
end
The commands path/to/file:XX syntax is made up by me. Because the NUM in commands NUM syntax requires exactly the breakpoint's runtime ID number (assigned by GDB), I can not use a deterministic syntax for that purpose.
I'm currently registering breakpoints via a text file with such a content:
break ./main.c:18
break ./io.c:29
and then issuing source breakpoints.txt command inside GDB. It seems that there is no way to register commands at the same time while registering a breakpoint:
(gdb) help break
Set breakpoint at specified line or function.
break [PROBE_MODIFIER] [LOCATION] [thread THREADNUM] [if CONDITION]
PROBE_MODIFIER shall be present if the command is to be placed in a
probe point. Accepted values are -probe' (for a generic, automatically guessed probe type), -probe-stap' (for a SystemTap probe) or
`-probe-dtrace' (for a DTrace probe).
LOCATION may be a line number, function name, or "*" and an address.
If a line number is specified, break at start of code for that line.
If a function is specified, break at start of code for that function.
If an address is specified, break at that exact address.
With no LOCATION, uses current execution address of the selected
stack frame. This is useful for breaking on return to a stack frame.
THREADNUM is the number from "info threads".
CONDITION is a boolean expression.
Multiple breakpoints at one place are permitted, and useful if their
conditions are different.
Question
Is there any easy way to set some predetermined commands for a predetermined breakpoint from within a file?
If not, is there any equivalent way to pass the (gdb) info breakpoints output to a file or a program while pipe is not available in GDB (version 5.3)? Currently I'm trying a workaround by using logging feature for that purpose:
set logging file /tmp/breakpoints
set logging on
info breakpoints
set logging off
Is there any easy way to set some predetermined commands for a predetermined breakpoint from within a file?
Yes: if you use commands without NUM, the commands will apply to the last breakpoint set. So you want something like:
break main.c:18
commands
silent
print buffer[0]
cont
end
I am looking for a program to observe the execution stack of a c/c++ program. Currently I am using gdb for this purpose.
The following command shows the content of the stack:
x/12xg $rsp
to execute instruction after instruction I am using
stepi
Is it possible to combine these to commands so that I would be able to stept through the assembly code and observing the stack? If you have another possible solution/program I am looking forward to hear that as well.
You can combine commands using define, like:
(gdb) define mystep
> stepi
> x/whatever $rsp
> end
Now mystep should step and then dump some memory.
I am using Lauterbach to debug a PowerPC embedded C software. I want to execute the below ALGO from a .cmm(PRACTICE) script. Pleas let me know if it is possible:
Set Breakpoint
When Breakpoint is hit, execute a .cmm file. This .cmm file will rewrite the values of an array.
Continue execution of program
I don't want to stub the whole function. The code has to be untouched.
Set the breakpoint with
Break.Set <addr> /Program /CMD "DO myScript.cmm"
To continue the execution of the target program, add the command Go to the end of the called PRACTICE script.
If you can't add the command Go to the end of the called PRACTICE script, you'll need a veneer-script like this:
// Content of myScript.cmm
DO myAlgorithm.cmm
Go
ENDDO
The Break.Set command knows also an option /RESUME, but this is not suitable for your case, since it won't wait until the called PRACTICE script has finished.
As you have mentioned !
I don't want to stub the whole function. The code has to be untouched.
You can try this;
;set a breakpoint on function
BREAK.SET <function_name/addr>\<LINE NUMBER>
;store address of current program counter(PC)
&pc=r(pc)
&call=address.offset(<function_name/addr>\<LINE NUMBER>) ;This will give the address of a function where breakpoint is set.
;Compare the address if it hit on correct function
IF (&pc==&call)
Do call_meonceHIT.cmm ;your desired .cmm script.
Break.Delete /ALL ; to delete all the set breakpoint.
This will make sure that breakpoint is hitting correct function or runnable.
I have read the following SO question:
Do specific action when certain breakpoint hits in gdb
Here, we use 'command' to decide what to do when the SPECIFIED Breakboint Gets Hit.
My Question is:
Suppose I put Breakpoints on ALL the Functions matching a given pattern:
gdb$rbreak func_
=> 100 Breakpoints (say)
When I execute this Code, I want to do the SAME Action - on hitting Each of these functions.
Hence, I cannot define something like:
command break_point_number
// since I don't know how many breakpoints will be there
Can somebody please suggest me:
How can I do a specific action-set when ANY Breakpoint gets Hit in GDB?
Thanks.
With a new enough version of gdb you can use a range:
(gdb) rbreak whatever
... gdb creates breakpoints N, N+1, ..., M
(gdb) commands N-M
> stuff
> end
I forget exactly when this feature went in.
With an older version of gdb, I'm not sure it can easily be done.
It can be done with difficulty: use set logging to write output to a file, then "info break", then "shell" to run scripts to edit the file into gdb commands, then "source". This is very painful.
If I set a watchpoint for a variable local to the current scope, it will be auto deleted when going out of the scope. Is there any way to set it once and keep it auto alive whenever entering the same scope?
Is there anyway to set conditional watchpoint, like watch var1 if var1==0? In my case, the condition does't work. gdb stops whenever var1's value is changed, instead of untill var1 == 0 is true. My gdb is GNU gdb 6.8-debian.
I agree with Dave that a conditional breakpoint is the way to go.
However, to do what you asked, you can use GDB's commands command to set a list of GDB commands to execute whenever a breakpoint is hit. I find this incredibly useful.
I suggest writing your GDB commands into a file so that they are easy to edit and easy to reload with the source command. Or you can specify command files to load on the GDB command line or use .gdbinit to make them load automatically.
An example of a good use of commands:
Suppose that I have a function format that is called by a lot of other functions. I want to break on it, but only after function do_step_3 has been called.
break do_step_3
commands
break format
continue
end
You could use this for your problem with something like:
break func
commands
watch var
continue
end
You can set conditions on watchpoints in the same way that you do with breakpoints. This is in the documentation but admittedly it hardly calls attention to itself.
So watch my_var if my_var > 3 works just fine, as does the condition command.
To recreate the watchpoint if the variable it is watching goes out of scope, have gdb do this automatically using a breakpoint at the start of the function as Zan has described.
You can set a watchpoint that does not go out of scope by setting it to the memory address.
(gdb) p &var1
$1 = (int *) 0x41523c0
(gdb) watch *(int *)0x41523c0
Hardware watchpoint 1: *(int *)0x41523c0
This also works for other data types and pointers.
I'm not sure which language us are using, so the exact answer will vary, but could you change the variable to either be static, global, or dynamically allocated (and don't free it when the function returns?). This way it's raw address won't change, and gdb will be able breakpoint on it.
Instead of watching the value whe it equals a specific value; you should set a conditional break point on the line where you want to check the value of var1. This should effectively have the same effect
e.g.
(gdb) break main.c:123 if (var1 == 0)