lldb can't debug string when compiled by clang++

Question

This is the test code.

#include <string>

int main(int argc, char const *argv[]) {
    std::string a = "hello";
    std::string b = "world";
    return 0;
}

I compile it by the command:

clang++ test.cpp -g

Then I try to debug it:

lldb a.out

I add break at 4th line, after the a = "hello" runs. I try to print the a by p a, it show me the following error:

error: incomplete type 'string' (aka 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >') where a complete type is requ
ired

note: forward declaration of 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >'
error: 1 errors parsing expression

I can't figure out.

Though when I try to compile by g++, it's OK.

Hypotenuse

A wild guess - the compiler optimized it away, because it is unused, and then did not include the type definitions (as they are 'no longer needed'). Now the debugger cannot access them. – Formerly

Have you tested on your computer? Is that just happen on me? – Hypotenuse

Answer 1

This is because clang is not emitting debug information for std::string. Make sure that you installed debug info for libstdc++. See this invalid bug for more information:

Looks like you don't have debug information for libstdc++ installed:

Missing separate debuginfos, use: dnf debuginfo-install libgcc-5.1.1-4.fc22.x86_64 libstdc++-5.1.1-4.fc22.x86_64

Clang is not emitting debug information for std::string because it was told that libstdc++ provides it (but in your case, it's not installed); this is a debug size optimization that GCC apparently doesn't perform.

Hertha

Answer 2

I was able to resolve the problem by adding -fstandalone-debug after clang++.

(lldb) r
Process 9391 launched: '/workspaces/cs15/hw4/CalcYouLater' (x86_64)
Process 9391 stopped
* thread #1, name = 'CalcYouLater', stop reason = breakpoint 1.1
    frame #0: 0x0000000000402ab7 CalcYouLater`RPNCalc::processCommand(this=0x00007fffffffd138, cmd="{") at RPNCalc.cpp:92:17
   89    */
   90   void RPNCalc::processCommand(string cmd) {
   91       int value;
-> 92       if (got_int(cmd, &value)) {
   93           processInt(value);
   94       } else if (cmd == "#t" or cmd == "#f") {
   95           processBool(cmd);
(lldb) p cmd
(std::string) $0 = "{"
(lldb) 

My testing environment is 22.04.1-Ubuntu SMP Wed Jan 10 22:57:03 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux.

Danaides

Answer 3

Try compiling with -glldb instead of -g, it compiles with optimized degub information for lldb

Miscarriage