[lldb] `error: unknown error` while starting lldb's clang repl

[anutosh491]

Hi,

I've been educating myself with the lldb REPL. So I thought of going through this example TestClangRepl.py

So 1 create a simple a.out (main returning 0) -> set breakpoint on main and run -> followed by expression --repl -l c -- to see this

anutosh491@Anutoshs-MacBook-Air SDKs % lldb /Users/anutosh491/work/xeus-cpp/a.out
(lldb) target create "/Users/anutosh491/work/xeus-cpp/a.out"
Current executable set to '/Users/anutosh491/work/xeus-cpp/a.out' (arm64).
(lldb) breakpoint set -n main
Breakpoint 1: where = a.out`main + 24 at main.c:2:3, address = 0x0000000100003fa0
(lldb) run
Process 91181 launched: '/Users/anutosh491/work/xeus-cpp/a.out' (arm64)
Process 91181 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100003fa0 a.out`main(argc=1, argv=0x000000016fdff638) at main.c:2:3
   1       int main(int argc, char **argv) {
-> 2         return 0;
   3       }
Target 0: (a.out) stopped.
(lldb) expression --repl -l c -- 
error: unknown error
  1> 1  + 1
(int) $0 = 2

Now I see this thing error: unknown error which is probably showing up cause a return is missing here and we continue (expr is empty! So EvaluateExpression fails and prints this)

And I also see this

(lldb) expression --repl -l c -- 3 + 3
(int) $1 = 6
  2> 

Curious if this should even happen (I am guessing not cause expressions should only be evaluated inside the repl when we use --repl) . Probably can use return as I said with something like

if (!expr.empty()) {
    result.GetOutputStream().Printf(
        "[LOG] Warning: trailing input is ignored in --repl mode\n");
}

Tagging @JDevlieghere as I'm not sure who maintains the lldb repl code.

I could push a patch with the above solution I proposed if that makes sense. Thanks !

[llvmbot]

@llvm/issue-subscribers-lldb

Author: Anutosh Bhat (anutosh491)

Hi,

I've been educating myself with the lldb REPL. So I thought of going through this example TestClangRepl.py

So 1 create a simple a.out (main returning 0) -> set breakpoint on main and run -> followed by expression --repl -l c -- to see this

anutosh491@<!-- -->Anutoshs-MacBook-Air SDKs % lldb /Users/anutosh491/work/xeus-cpp/a.out
(lldb) target create "/Users/anutosh491/work/xeus-cpp/a.out"
Current executable set to '/Users/anutosh491/work/xeus-cpp/a.out' (arm64).
(lldb) breakpoint set -n main
Breakpoint 1: where = a.out`main + 24 at main.c:2:3, address = 0x0000000100003fa0
(lldb) run
Process 91181 launched: '/Users/anutosh491/work/xeus-cpp/a.out' (arm64)
Process 91181 stopped
* thread #<!-- -->1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #<!-- -->0: 0x0000000100003fa0 a.out`main(argc=1, argv=0x000000016fdff638) at main.c:2:3
   1       int main(int argc, char **argv) {
-&gt; 2         return 0;
   3       }
Target 0: (a.out) stopped.
(lldb) expression --repl -l c -- 
error: unknown error
  1&gt; 1  + 1
(int) $0 = 2

Now I see this thing error: unknown error which is probably showing up cause a return is missing here and we continue (expr is empty! So EvaluateExpression fails and prints this)

And I also see this

(lldb) expression --repl -l c -- 3 + 3
(int) $1 = 6
  2> 

Curious if this should even happen (I am guessing not cause expressions should only be evaluated inside the repl when we use --repl) . Probably can use return as I said with something like

if (!expr.empty()) {
    result.GetOutputStream().Printf(
        "[LOG] Warning: trailing input is ignored in --repl mode\n");
}

Tagging @JDevlieghere as I'm not sure who maintains the lldb repl code.

I could push a patch with the above solution I proposed if that makes sense. Thanks !

[jimingham]

I don't think the C-based REPL has been made to work yet. For instance:

(lldb) expr --repl -l c --
error: unknown error
  1> int a_var = 100
  2> printf("%d\n", a_var)
                    ˄
                    ╰─ error: use of undeclared identifier 'a_var'

That shows the error you saw, but more importantly the point of the repl is that you are adding defines to the repl environment, and they will be looked up there, without having to make "persistent expression variables" by using an initial $ for all your identifiers.

Also:

  2> int a_func (int input) { return input * 1000; }
                            ˄
                            ╰─ error: function definition is not allowed here

The REPL is supposed to be implicitly --top-level but for C it clearly isn't.