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

[aahrun]

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.

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[llvmbot]

@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.

[da-viper]

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

[aahrun]

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]

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]

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

[da-viper]

Yeah It isn't

[da-viper]

LGTM!
Modulo the #include

[aahrun]

@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]

Thanks

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