[lldb-dev] Breakpoint + callback performance ... Can it be faster?

[Pavel Labath via lldb-dev]

Every time you use the "expr" command, we compile a tiny c++ code
snippet inject it into the target process and execute it. If you type
"log enable lldb expr" you should be able to follow how exactly that
works. You can use pretty much any c++ construct in the expression
including declaring variables/types:
(lldb) expr -- char s[]="qwerty"; for(int i=0; i < sizeof s; ++i)
printf("%d: %c\n", i, s[i]);
0: q
1: w
2: e
3: r
4: t
5: y
6:


So, if your question is "do we support compiling code and running it
in the debugged process", then the answer is yes. If you want
something that would automatically intercept some function to execute
your code while the process is running (some kind of dynamic
instrumentation), then the answer is no. (But I don't see any mention
of that on the gdb page you quoted either).

cheers,
pavel

On 12 February 2017 at 18:34, Roman Popov via lldb-dev
<lldb-dev at lists.llvm.org> wrote:
> Hello Benjamin , all
>
>>>I recently started using lldb to write a basic instrumentation tool for
>>>tracking the values of variables at various code-points in a program.
>
> I have the same problem of tracing some variables and debugging application
> post-mortem. Without knowing about your experience I've started walking same
> path and encountered same problem. In my case inserting an empty callback
> slows-down application by 100x. This is not acceptable for me, because
> instead of minutes I got hours of runtime.
>
> Did you found any faster solution?
>
> My current plan is to solve it with code injection: I plan to find pointers
> to interesting values using debugger scripting and then inject code to trace
> them.
>
> Does LLDB supports code injection ? I've found information only about gdb
> https://sourceware.org/gdb/onlinedocs/gdb/Compiling-and-Injecting-Code.html
> but not about lldb
>
>
> -Roman
>
>
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