"error: summary string parsing error" on Fedora 30

Subprojects LLDB
1

With Clang 8.0.0 and libstd++ 9.1.1 on Fedora 30 x86_64, I get this
error from LLDB when trying to see the value of a string:

"error: summary string parsing error"

The code is simply:

std::string msg{"foo bar baz"};

With libcxx 8.0.0, instead of the above error, I simply see "??" when
inspecting the msg variable.

All of the above works fine for me in Ubuntu 19.04. I only have the
problem with Fedora 30. Tried in both CLion and VS Code.

How should I troubleshoot this? Could I be missing a package?

2

We have a summary provider for std::string that is built into LLDB that must not be working with the C++ runtime you are using. The current summary string that is used is in source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp in LoadLibStdcppFormatters:

lldb::TypeSummaryImplSP std_string_summary_sp(
new StringSummaryFormat(stl_summary_flags, “${var._M_dataplus._M_p}”));

So do a “frame var --raw msg” and see what the members of your std::string look like. I am guessing you won’t see “_M_dataplus” or “_M_p” in there. The “${var” means your std::string variable, and we are trying to access “msg._M_dataplus._M_p” to see what the string looks like.

3

Thanks for the info. "frame var --raw msg" is empty on my Fedora 30
system, but populated correctly on Ubuntu 19.04. E.g., on Fedora 30:

(lldb) frame var --raw msg
(std::string) msg = {}

I compiled with "clang++ -g main.cpp". Nothing fancy. Installed
Clang with "dnf install clang". Again, nothing fancy.

I'm a LLVM newb. Can you point me in the right direction?

4

Sounds like the compiler omitted the type info for std::string. Try "-glldb" in your compiler flags. This tunes debug info for LLDB. A lot of compilers will try to omit types from debug info if the type doesn't originate in the current executable. std::string would be one of those classes. If that flag doesn't work, then you might try -fno-limit-debug-info.

Let me know if that helps!

5

Thanks, Greg. Using "-g -fno-limit-debug-info" did the trick. All
works as expected now. Apparently the versions which ship with Ubuntu
19.04 and Fedora 30 differ with respect to this flag.

6

Sounds like the compiler omitted the type info for std::string. Try "-glldb" in your compiler flags. This tunes debug info for LLDB. A lot of compilers will try to omit types from debug info if the type doesn't originate in the current executable. std::string would be one of those classes. If that flag doesn't work, then you might try -fno-limit-debug-info.

Thanks, Greg. Using "-g -fno-limit-debug-info" did the trick. All works as expected now.

Great! Glad I could help.

Apparently the versions which ship with Ubuntu 19.04 and Fedora 30 differ with respect to this flag.

So are you saying "-glldb" is wrong on Fedora but "-fno-limit-debug-info" works?

7

On Fedora 30:

-g: no debug info
-glldb: no debug info
-g -glldb: no debug info
-g -fno-limit-debug-info: debug info present

I'm trying to determine if "-fno-limit-debug-info" is enabled by
default on Fedora 30, but don't have it it figured out yet.

8

Seems like you should fix "-g" so it emits debug info and then try to figure this out after that.

9

Behavior of the -g variants is probably better discussed on llvm-dev.
--paulr