[lldb] Avoid a crash after selecting an unknown platform

[igorkudrin]

PlatformList::Create() added an item in the list even if Platform::Create() returned nullptr. Other methods use items of the list without checking, which can lead to a crash. For example:

> lldb
(lldb) platform select unknown
error: unable to find a plug-in for the platform named "unknown"
(lldb) file a.out-arm64
PLEASE submit a bug report to...
Stack dump:
0.      Program arguments: lldb
1.      HandleCommand(command = "file a.out-arm64 ")
...

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Igor Kudrin (igorkudrin)

Changes

PlatformList::Create() added an item in the list even if Platform::Create() returned nullptr. Other methods use items of the list without checking, which can lead to a crash. For example:

> lldb
(lldb) platform select unknown
error: unable to find a plug-in for the platform named "unknown"
(lldb) file a.out-arm64
PLEASE submit a bug report to...
Stack dump:
0.      Program arguments: lldb
1.      HandleCommand(command = "file a.out-arm64 ")
...

---

Full diff: https://github.com/llvm/llvm-project/pull/151803.diff

2 Files Affected:

• (modified) lldb/source/Target/Platform.cpp (+2-1)
• (modified) lldb/unittests/Platform/PlatformTest.cpp (+6)

diff --git a/lldb/source/Target/Platform.cpp b/lldb/source/Target/Platform.cpp
index e9d9c8f0976b6..8681adaf5ea76 100644
--- a/lldb/source/Target/Platform.cpp
+++ b/lldb/source/Target/Platform.cpp
@@ -2234,7 +2234,8 @@ PlatformSP PlatformList::GetOrCreate(llvm::ArrayRef<ArchSpec> archs,
 PlatformSP PlatformList::Create(llvm::StringRef name) {
   std::lock_guard<std::recursive_mutex> guard(m_mutex);
   PlatformSP platform_sp = Platform::Create(name);
-  m_platforms.push_back(platform_sp);
+  if (platform_sp)
+    m_platforms.push_back(platform_sp);
   return platform_sp;
 }
 
diff --git a/lldb/unittests/Platform/PlatformTest.cpp b/lldb/unittests/Platform/PlatformTest.cpp
index 8ab223ea2cd57..6299197791fc4 100644
--- a/lldb/unittests/Platform/PlatformTest.cpp
+++ b/lldb/unittests/Platform/PlatformTest.cpp
@@ -157,3 +157,9 @@ TEST_F(PlatformTest, GetPlatformForArchitecturesCandidates) {
 
   PlatformThumb::Terminate();
 }
+
+TEST_F(PlatformTest, CreateUnknown) {
+  SetHostPlatform(std::make_shared<PlatformIntel>());
+  ASSERT_EQ(list.Create("unknown-platform-name"), nullptr);
+  ASSERT_EQ(list.GetOrCreate("dummy"), nullptr);
+}