LLDB (debugger)

LLDB

Developer(s)	LLVM Developer Group
Repository	github.com/llvm/llvm-project
Written in	C++
Operating system	macOS i386 and x86-64, Linux, FreeBSD, Windows
Type	Debugger
License	UIUC (BSD-style) Apache License 2.0 with LLVM Exceptions (v9.0.0 or later)
Website	lldb.llvm.org

The LLDB Debugger (LLDB) is the debugger component of the LLVM project. It is built as a set of reusable components which extensively use existing libraries from LLVM, such as the Clang expression parser and LLVM disassembler. LLDB is free and open-source software under the University of Illinois/NCSA Open Source License, a BSD-style permissive software license. Since v9.0.0, it was relicensed to the Apache License 2.0 with LLVM Exceptions.

Current state

LLDB supports debugging of programs written in C, Objective-C, and C++. The Swift community maintains a version which adds support for the language. It is known to work on macOS, Linux, FreeBSD, and Windows, and supports i386, x86-64, and ARM instruction sets. LLDB is the default debugger for Xcode 5 and later. It can be used from other IDEs, including Visual Studio Code, Eclipse, and CLion.

Features matrix

Feature	FreeBSD	Linux	macOS	Windows
Backtracing
Breakpoints
C++11:				?
Command-line lldb tool
Core file debugging
Debugserver (remote debugging)	Not ported	Not ported		Not ported
Disassembly
Expression evaluation	?	Works with some bugs		Works with some bugs
JIT debugging	?	Symbolic debugging only	Untested
Objective-C 2.0:	?	—		—

An example session

Consider the following source-code written in C:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

size_t foo_len( const char *s )
{
  return strlen( s );
}

int main( int argc, char *argv[] )
{
  const char *a = NULL;

  printf( "size of a = %lu\n", foo_len(a) );

  exit( 0 );
}

Using the Clang compiler on Linux, the code above must be compiled using the -g flag in order to include appropriate debug information on the binary generated, thus making it possible to inspect it using LLDB. Assuming that the file containing the code above is named example.c, the command for the compilation could be:

$ clang example.c -Og -g -o example

And the binary can now be run:

$ ./example
Segmentation fault

Since the example code, when executed, generates a segmentation fault, LLDB can be used to inspect the problem.

$ lldb ./example
(lldb) target create "./example"
Current executable set to './example' (x86_64).
(lldb) run
Process 7652 launched: '/path/example' (x86_64)
Process 7652 stopped
* thread #1, stop reason = Exception 0xc0000005 encountered at address 0x7ff75da1b801
    frame #0: 0x00007ff75da1b801 example
->  0x7ff75da1b801: movq   (%rax), %rdx
    0x7ff75da1b804: movq   %r8, %r9
    0x7ff75da1b807: addq   $0x8, %rax
    0x7ff75da1b80b: addq   %rdx, %r9

The problem is occurs when calling the function strlen (because its argument, s, is NULL). Depending on the implementation of strlen (inline or not), the output can be different.

See also

• GNU Debugger
• Microsoft Visual Studio Debugger
• VOGL

External links

• Official website
• Supported LLDB Versions in Qt Creator