[lldb-dev] [Bug 22211] New: Can't easily call a function in a binary without debug information, even if I can break on it

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22211

            Bug ID: 22211
           Summary: Can't easily call a function in a binary without debug
                    information, even if I can break on it
           Product: lldb
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: lldb-dev at cs.uiuc.edu
          Reporter: mstange at themasta.com
    Classification: Unclassified

I'd like to easily be able to attach lldb to a Firefox Nightly build and call a
function called mozilla_sampler_save_profile_to_file, like this:

> (lldb) print (void)mozilla_sampler_save_profile_to_file("/Users/mstange/Desktop/profile.txt")

But since this binary doesn't come with debugging information, lldb gives me an
error:
> error: use of undeclared identifier 'mozilla_sampler_save_profile_to_file'

It can, however, break on the  function:
> (lldb) b mozilla_sampler_save_profile_to_file
> Breakpoint 1: where = XUL`mozilla_sampler_save_profile_to_file(char const*), address = 0x000000010253d2a0

As a user of lldb, I can now take that address, cast it to a function pointer,
and call the function through that pointer:
> (lldb) p ((void(*)(const char*))0x000000010253d2a0)("/Users/mstange/Desktop/profile.txt")

Or, instead of copy-pasting the address, I can do a little scripting:
> (lldb) script
> Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
> >>> lldb.debugger.HandleCommand('print ((void(*)(const char*))0x%0x)("/Users/mstange/Desktop/profile.txt")' % lldb.target.FindFunctions("mozilla_sampler_save_profile_to_file").symbols[0].addr.load_addr)

It would be nice if lldb could simplify this process for me. It knows the
address of the function already, and it could theoretically derive the argument
types from the demangled function name.

In https://bugzilla.mozilla.org/show_bug.cgi?id=1118228 I'm adding a user
defined lldb function called 'callfunc' to the lldb helpers that are included
in the Firefox source, which makes this a little easier.

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