On MacOSX lldb needs to be code signed. The Debug, DebugClang and Release builds are set to code sign using a code signing certificate named lldb_codesign. If you have re-installed a new OS, please delete all old lldb_codesign items from your keychain. There will be 3: a code signing certification and a public and private key. Reboot after deleting them. You will also need to delete and build folders that contained old signed items. The darwin kernel will cache code sigining using the executable's file system node, so you will need to delete the file so the kernel clears its cache. If you don't have one yet you will need to: - Launch /Applications/Utilities/Keychain Access.app - In Keychain Access select the "login" keychain in the "Keychains" list in the upper left hand corner of the window. - Select the following menu item: Keychain Access->Certificate Assistant->Create a Certificate... - Set the following settings Name = lldb_codesign Identity Type = Self Signed Root Certificate Type = Code Signing - Click Create - Click Continue - Click Done - Click on the "My Certificates" - Double click on your new lldb_codesign certificate - Turn down the "Trust" disclosure triangle Change: When using this certificate: Always Trust - Enter your login password to confirm and make it trusted The next steps are necessary on SnowLeopard, but are probably because of a bug how Keychain Access makes certificates. [Note: These also apply for Lion and Mountain Lion.] - Drag the new lldb_codesign certificate from the login keychain to the System keychain in the Keychains pane of the main Keychain Access window to make a copy of this certificate in the System keychain. You'll have to authorize a few more times, set it to be "Always trusted" when asked. - Make sure there is no "~/Desktop/lldb_codesign.cer" file on your desktop, if there is one, delete it first, otherwise when you drag a copy of the lldb_codesign certificate to your desktop it will get renamed as "lldb_codesign_1.cer" and the security command you run below will trust the old incorrect certificate. - Switch to the System keychain, and drag the copy of lldb_codesign you just made there onto the desktop. - Switch to Terminal, and run the following: sudo security add-trust -d -r trustRoot -p basic -p codeSign -k /Library/Keychains/System.keychain ~/Desktop/lldb_codesign.cer rm -f ~/Desktop/lldb_codesign.cer - Right click on the "lldb_codesign" certificate in the "System" keychain (NOT "login", but the one in "System"), and select "Delete" to delete it from the "System" keychain. - Reboot - Clean by removing all previously creating code signed binarires and rebuild lldb and you should be able to debug. That should do it.