[clangd] Parsing error crash

[miEsMar]

Hi all, I've hit a clangd parsing error which resulted in a crash (segfault?).

Here is the error message:

[ERROR][2025-09-10 17:08:24] ...p/_transport.lua:36	"rpc"	"clangd"	"stderr"	"I[17:08:24.078] clangd version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)\nI[17:08:24.078] Features: linux+grpc\nI[17:08:24.078] PID: 115544\nI[17:08:24.078] Working directory: ~/repos/XBSF\nI[17:08:24.078] argv[0]: clangd\nI[17:08:24.078] argv[1]: --background-index\nI[17:08:24.078] argv[2]: --clang-tidy\nI[17:08:24.078] argv[3]: --header-insertion=iwyu\nI[17:08:24.078] argv[4]: --completion-style=detailed\nI[17:08:24.078] argv[5]: --function-arg-placeholders\nI[17:08:24.078] argv[6]: --fallback-style=llvm\nE[17:08:24.078] Value specified by --function-arg-placeholders is invalid. Provide a boolean value or leave unspecified to use ArgumentListsPolicy from config instead.\nI[17:08:24.078] Starting LSP over stdin/stdout\nI[17:08:24.078] <-- initialize(1)\nI[17:08:24.080] --> reply:initialize(1) 1 ms\n"

[...]

[ERROR][2025-09-10 17:08:37] ...p/_transport.lua:36	"rpc"	"clangd"	"stderr"	"PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.\n
    Stack dump:
    0.\t~/repos/XBSF/xbsf/renderer/api.c:68:5 <Spelling=~/repos/XBSF/xbsf/renderer/../util/string.h:34:46>: current parser token ')'
    1.\t~/repos/XBSF/xbsf/renderer/api.c:64:1: parsing function body '_api_create_pipeline'
    2.\t~/repos/XBSF/xbsf/renderer/api.c:64:1: in compound statement ('{}')
    3.\t~/repos/XBSF/xbsf/renderer/api.c:68:5 <Spelling=~/repos/XBSF/xbsf/renderer/../util/string.h:33:8>: in compound statement ('{}')"

A MRE which resembles the lines reported in the error message is of the like:

#include <string.h>

#define STRING_APPEND(strptr, str)                                                                 \
    do {                                                                                           \
        strcpy((strptr + strlen(strptr)), str);                                                    \
        strptr[strlen(strptr)] = '\0';                                                             \
    } while (0)

#define _SHADERS_ROOT_DIR_POSTFIX "/xbsf/renderer/shaders/"

int main(void)
{
    char vert_full_path[256] = {'\0'};
    char frag_full_path[256] = {'\0'};
    STRING_APPEND(vert_full_path, "");
    STRING_APPEND(vert_full_path, _SHADERS_ROOT_DIR_POSTFIX "vert.spv");
    STRING_APPEND(frag_full_path, "");
    STRING_APPEND(frag_full_path, _SHADERS_ROOT_DIR_POSTFIX "frag.spv");

    return 0;
}

Platform: Linux, Ubuntu.
The .clangd file:

CompileFlags:
  Add: [
    -DXBSF_DEBUG,
    -DXBSF_ENABLE_GPU,
    -DXBSFGPU_CUDA,
    -DXBSF_UTIL_STRING_IMPLEMENTATIONS,
    -DXBSF_GRAPHICS_USE_GUI,
    -I./xbsf,
    -I./xbsf/include,
    -I./xbsf/gui/include,
    -isystem,
    ./deps/cuda,
    -isystem,
    ./deps/nvrtc,
    -std=c11
  ]
  Compiler: gcc-12

EDIT:

For conciseness:

• util/string.h:34:46>: current parser token ')' is the closing ) of the strcpy command within the STRING_APPEND macro.
• api.c:64:1: in compound statement ('{}') is the first column char one line down the opening { for the function body, as in the main function in the MRE.
• util/string.h:33:8>: in compound statement ('{}')" is the next char after the { in do { within the STRING_APPEND macro.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: mEm (miEsMar)

Hi all, I've hit a `clangd` parsing error which resulted in a crash (segfault?).

Here is the error message:

[ERROR][2025-09-10 17:08:24] ...p/_transport.lua:36	"rpc"	"clangd"	"stderr"	"I[17:08:24.078] clangd version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)\nI[17:08:24.078] Features: linux+grpc\nI[17:08:24.078] PID: 115544\nI[17:08:24.078] Working directory: ~/repos/XBSF\nI[17:08:24.078] argv[0]: clangd\nI[17:08:24.078] argv[1]: --background-index\nI[17:08:24.078] argv[2]: --clang-tidy\nI[17:08:24.078] argv[3]: --header-insertion=iwyu\nI[17:08:24.078] argv[4]: --completion-style=detailed\nI[17:08:24.078] argv[5]: --function-arg-placeholders\nI[17:08:24.078] argv[6]: --fallback-style=llvm\nE[17:08:24.078] Value specified by --function-arg-placeholders is invalid. Provide a boolean value or leave unspecified to use ArgumentListsPolicy from config instead.\nI[17:08:24.078] Starting LSP over stdin/stdout\nI[17:08:24.078] <-- initialize(1)\nI[17:08:24.080] --> reply:initialize(1) 1 ms\n"

[...]

[ERROR][2025-09-10 17:08:37] ...p/_transport.lua:36	"rpc"	"clangd"	"stderr"	"PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.\n
    Stack dump:
    0.\t~/repos/XBSF/xbsf/renderer/api.c:68:5 <Spelling=~/repos/XBSF/xbsf/renderer/../util/string.h:34:46>: current parser token ')'
    1.\t~/repos/XBSF/xbsf/renderer/api.c:64:1: parsing function body '_api_create_pipeline'
    2.\t~/repos/XBSF/xbsf/renderer/api.c:64:1: in compound statement ('{}')
    3.\t~/repos/XBSF/xbsf/renderer/api.c:68:5 <Spelling=~/repos/XBSF/xbsf/renderer/../util/string.h:33:8>: in compound statement ('{}')"

A MRE which resembles the lines reported in the error message is of the like:

#include <string.h>

#define STRING_APPEND(strptr, str)                                                                 \
    do {                                                                                           \
        strcpy((strptr + strlen(strptr)), str);                                                    \
        strptr[strlen(strptr)] = '\0';                                                             \
    } while (0)

#define _SHADERS_ROOT_DIR_POSTFIX "/xbsf/renderer/shaders/"

int main(void)
{
    char vert_full_path[256] = {'\0'};
    char frag_full_path[256] = {'\0'};
    STRING_APPEND(vert_full_path, "");
    STRING_APPEND(vert_full_path, _SHADERS_ROOT_DIR_POSTFIX "vert.spv");
    STRING_APPEND(frag_full_path, "");
    STRING_APPEND(frag_full_path, _SHADERS_ROOT_DIR_POSTFIX "frag.spv");

    return 0;
}

Platform: Linux, Ubuntu.
The .clangd file:

CompileFlags:
  Add: [
    -DXBSF_DEBUG,
    -DXBSF_ENABLE_GPU,
    -DXBSFGPU_CUDA,
    -DXBSF_UTIL_STRING_IMPLEMENTATIONS,
    -DXBSF_GRAPHICS_USE_GUI,
    -I./xbsf,
    -I./xbsf/include,
    -I./xbsf/gui/include,
    -isystem,
    ./deps/cuda,
    -isystem,
    ./deps/nvrtc,
    -std=c11
  ]
  Compiler: gcc-12

EDIT:

For conciseness:

• util/string.h:34:46>: current parser token ')' is the closing ) of the strcpy command within the STRING_APPEND macro.
• api.c:64:1: in compound statement ('{}') is the first column char one line down the opening { for the function body, as in the main function in the MRE.
• util/string.h:33:8>: in compound statement ('{}')" is the next char after the { in do { within the STRING_APPEND macro.

[HighCommander4]

A MRE which resembles the lines reported in the error message is of the like:

Just to clarify, does this minimal example trigger the crash for you? Or it just resembles code in a larger file that triggers the crash?

[miEsMar]

A MRE which resembles the lines reported in the error message is of the like:

Just to clarify, does this minimal example trigger the crash for you? Or it just resembles code in a larger file that triggers the crash?

It resembles the code that triggered the crash in a larger file. Moreover, the crash is not deterministic, as it does not happen every time I open that file. However, since the MRE code is 100% as the one that seems to have caused the crash, maybe it might be useful for executing iterative runs under a debugger, until something happens.

[HighCommander4]

Could you post the full stack trace from the crash (see https://clangd.llvm.org/troubleshooting#getting-stacktraces-from-crashes for how to symbolize it if needed)?

[miEsMar]

Unfortunately, I did not have llvm-symbolizer installed at the time of the crash.
All I see is:

[ERROR][2025-09-10 17:08:37] ...p/_transport.lua:36	"rpc"	"clangd"	"stderr"	"Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  clangd    0x00000000005556e7
1  clangd    0x00000000005535ae
2  clangd    0x000000000055602f
3  libc.so.6 0x00007da3e1242520
4  clangd    0x0000000000ba0d1d
5  clangd    0x00000000010d2468
6  clangd    0x00000000044a32d3
7  clangd    0x00000000044983a8
8  clangd    0x0000000004493069
9  clangd    0x00000000044a1f7a
10 clangd    0x0000000004495068
11 clangd    0x0000000004496ef4
12 clangd    0x0000000004493069
13 clangd    0x0000000004492f69
14 clangd    0x00000000044ebb25
15 clangd    0x00000000044ea190
16 clangd    0x00000000044e9a88
17 clangd    0x00000000044f1a93
18 clangd    0x00000000044ea44f
19 clangd    0x00000000044e9a88
20 clangd    0x00000000044edc6f
21 clangd    0x00000000044ea564
22 clangd    0x00000000044e9a88
23 clangd    0x00000000044f1a93
24 clangd    0x00000000044f2a80
25 clangd    0x000000000444afc0
26 clangd    0x0000000004467d94
27 clangd    0x000000000444a286
28 clangd    0x0000000004449c19
29 clangd    0x00000000044491f8
30 clangd    0x0000000004447569
31 clangd    0x0000000004443bfe
32 clangd    0x00000000040aaefd
33 clangd    0x00000000015ba9a4
34 clangd    0x0000000001639edf
35 clangd    0x000000000163da4b
36 clangd    0x0000000001636343
37 clangd    0x000000000163531d
38 clangd    0x00000000017ade06
39 libc.so.6 0x00007da3e1294ac3
40 libc.so.6 0x00007da3e1326850
Signalled during AST worker action: Update
Filename: ~/repos/XBSF/xbsf/renderer/api.c
Directory: ~/repos/XBSF
Command Line: /usr/bin/gcc-12 -DXBSF_DEBUG -DXBSF_ENABLE_GPU -DXBSFGPU_CUDA -DXBSF_UTIL_STRING_IMPLEMENTATIONS -DXBSF_GRAPHICS_USE_GUI -I./xbsf -I./xbsf/include -I./xbsf/gui/include -isystem ./deps/cuda -isystem ./deps/nvrtc -std=c11 -isystem /usr/include/c++/11 -isystem /usr/include/c++/11/backward -isystem /usr/local/include -isystem /usr/include -isystem /usr/include/x86_64-linux-gnu/c++/11 -isystem ~/openmpi-5.0.3/install/include -resource-dir=~/.local/share/nvim/mason/packages/clangd/clangd_20.1.8/lib/clang/20 -- ~/repos/XBSF/xbsf/renderer/api.c
Version: 11\n"

As you might see, the clangd binary is installed through the Mason Nvim package, which only ships the binary likely linked to statically compiled LLVM libraries.

However, with that MRE, someone should be able to run debug tests. I hope there is enough information to at least have an idea of where the issue might come from.
What bothers me is that I do not have the crash everytime I open that file. So, I wonder if I did a specific action (which I honestly don't remember) that triggered the crash.

[HighCommander4]

Sorry, I have no idea what additional diagnostic steps to take in the absence of a reproducer or even a stack trace.

Maybe others have ideas, or maybe in time you can update the issue with this information.

[miEsMar]

I've hit the same issue once again (on a different file, but same issue structure, with compund literal {}).
Can you please recommend how to properly install the llvm-symbolizer considered that I am using clangd through the default Nvim LSP package provider (Mason)?
Shall I install clangd locally to have it?
I really want to shine a light onto this crash.

[HighCommander4]

Can you please recommend how to properly install the llvm-symbolizer

Since you're on Ubuntu, I would recommend installing packages from https://apt.llvm.org/. Install the packages clangd-20 and llvm-20 (the latter includes llvm-symbolizer), and then configure your editor to use clangd-20 (which should now be in the PATH) as its language server binary.

[HighCommander4]

Install the packages clangd-20 and llvm-20

Actually, now that version 21 is out, you might as well install clangd-21 and llvm-21. Maybe the crash is fixed already :)