[lldb-dap] Fix segfault in JSONUtils.cpp when GetUUIDString() returns nullptr #169844

aahrun · 2025-11-27T17:53:45Z

When creating a stack frame in JSONUtils.cpp CreateStackFrame() the code constructs a std::string from module.GetUUIDString(), which can return nullptr in some cases (as documented in the implementation of SBModule::GetUUIDString()). This causes a segmentation fault when passed to the std::string constructor.

This fix adds a null check before constructing the UUID string, falling back to an empty string if nullptr is returned. The existing empty check ensures the moduleId field is omitted from the JSON when no UUID exists.

github-actions · 2025-11-27T17:54:07Z

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llvmbot · 2025-11-27T17:54:43Z

@llvm/pr-subscribers-lldb

Author: Aaron (aahrun)

Changes

When creating a stack frame in JSONUtils.cpp CreateStackFrame() the code constructs a std::string from module.GetUUIDString(), which can return nullptr in some cases (as documented in the implementation of SBModule::GetUUIDString()). This causes a segmentation fault when passed to the std::string constructor.

This fix adds a null check before constructing the UUID string, falling back to an empty string if nullptr is returned. The existing empty check ensures the moduleId field is omitted from the JSON when no UUID exists.

Full diff: https://github.com/llvm/llvm-project/pull/169844.diff

1 Files Affected:

(modified) lldb/tools/lldb-dap/JSONUtils.cpp (+2-1)

diff --git a/lldb/tools/lldb-dap/JSONUtils.cpp b/lldb/tools/lldb-dap/JSONUtils.cpp
index 81eadae03bb48..1cc01cd547582 100644
--- a/lldb/tools/lldb-dap/JSONUtils.cpp
+++ b/lldb/tools/lldb-dap/JSONUtils.cpp
@@ -554,7 +554,8 @@ llvm::json::Value CreateStackFrame(DAP &dap, lldb::SBFrame &frame,
 
   lldb::SBModule module = frame.GetModule();
   if (module.IsValid()) {
-    std::string uuid = module.GetUUIDString();
+    const char *uuid_cstr = module.GetUUIDString();
+    std::string uuid = uuid_cstr ? uuid_cstr : "";
     if (!uuid.empty())
       object.try_emplace("moduleId", uuid);
   }

DavidSpickett

Looks fine, only thing is whether it's easy to add a test for this, probably too much effort.

Nominate @da-viper as an lldb-dap expert to decide that.

lldb/tools/lldb-dap/JSONUtils.cpp

da-viper · 2025-11-28T10:48:17Z

we could also update it here. both the module_id type and the call to llvm::StringRef.

llvm-project/lldb/tools/lldb-dap/Handler/CompileUnitsRequestHandler.cpp

Lines 63 to 68 in 6c0d5aa

    
           const std::string module_id = 
        
               GetString(arguments, "moduleId").value_or("").str(); 
        
           int num_modules = dap.target.GetNumModules(); 
        
           for (int i = 0; i < num_modules; i++) { 
        
             auto curr_module = dap.target.GetModuleAtIndex(i); 
        
             if (module_id == curr_module.GetUUIDString()) {

Do you by any chance have a reproducible ? because on linux lldb create one using crc32 even when there is no buildid

lldb/tools/lldb-dap/JSONUtils.cpp

aahrun · 2025-11-28T14:47:14Z

we could also update it here. both the module_id type and the call to llvm::StringRef.

llvm-project/lldb/tools/lldb-dap/Handler/CompileUnitsRequestHandler.cpp

Lines 63 to 68 in 6c0d5aa

const std::string module_id =

GetString(arguments, "moduleId").value_or("").str();

int num_modules = dap.target.GetNumModules();

for (int i = 0; i < num_modules; i++) {

auto curr_module = dap.target.GetModuleAtIndex(i);

if (module_id == curr_module.GetUUIDString()) {

Do you by any chance have a reproducible ? because on linux lldb create one using crc32 even when there is no buildid

I don't have an easy reproducible - but the crash I'm observing comes about when trying to debug JITed code from a custom compiler.

aahrun · 2025-12-01T11:06:30Z

we could also update it here. both the module_id type and the call to llvm::StringRef.

llvm-project/lldb/tools/lldb-dap/Handler/CompileUnitsRequestHandler.cpp

Lines 63 to 68 in 6c0d5aa

const std::string module_id =

GetString(arguments, "moduleId").value_or("").str();

int num_modules = dap.target.GetNumModules();

for (int i = 0; i < num_modules; i++) {

auto curr_module = dap.target.GetModuleAtIndex(i);

if (module_id == curr_module.GetUUIDString()) {

@da-viper I've extended the fix to cover this too. Let me know what you think.

alycm · 2025-12-01T11:08:38Z

lldb/tools/lldb-dap/Handler/CompileUnitsRequestHandler.cpp

 #include "EventHelper.h"
 #include "JSONUtils.h"
 #include "RequestHandler.h"
+#include "llvm/ADT/StringRef.h"


I suspect this line is not required as GetString was already used and returns a StringRef?

Yeah It isn't

da-viper

LGTM!
Modulo the #include

aahrun · 2025-12-01T15:00:20Z

@da-viper Thanks for the save. I am not able to merge, so if you're happy to proceed with the merge then I would appreciate it.

da-viper · 2025-12-01T15:06:59Z

Thanks

github-actions · 2025-12-01T15:07:07Z

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… nullptr (llvm#169844) When creating a stack frame in JSONUtils.cpp CreateStackFrame() the code constructs a std::string from module.GetUUIDString(), which can return nullptr in some cases (as documented in the implementation of SBModule::GetUUIDString()). This causes a segmentation fault when passed to the std::string constructor. This fix adds a null check before constructing the UUID string, falling back to an empty string if nullptr is returned. The existing empty check ensures the moduleId field is omitted from the JSON when no UUID exists. rdar://163811812 --------- Co-authored-by: Ebuka Ezike <[email protected]>

aahrun requested a review from JDevlieghere as a code owner November 27, 2025 17:53

llvmbot added lldb lldb-dap labels Nov 27, 2025

DavidSpickett reviewed Nov 28, 2025

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da-viper reviewed Nov 28, 2025

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aahrun force-pushed the fix-lldb-dap-jit-crash branch from 679089e to e2e10eb Compare November 28, 2025 15:09

alycm reviewed Dec 1, 2025

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da-viper approved these changes Dec 1, 2025

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aahrun force-pushed the fix-lldb-dap-jit-crash branch from 2a86e72 to 8be0106 Compare December 1, 2025 13:58

aahrun requested review from aaronmondal, aaupov, ayermolo, fabianmcg, ftynse, grypp, keith, maksfb, makslevental, paschalis-mpeis, rafaelauler, rolfmorel, rupprecht, stellaraccident, yota9 and yozhu as code owners December 1, 2025 13:58

da-viper merged commit 10ceca8 into llvm:main Dec 1, 2025
12 checks passed

[lldb-dap] Fix segfault in JSONUtils.cpp when GetUUIDString() returns nullptr #169844

[lldb-dap] Fix segfault in JSONUtils.cpp when GetUUIDString() returns nullptr #169844

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