[lldb] Avoid duplicate vdso modules when opening core files

[labath]

Summary

When opening core files (and also in some other situations) we could end
up with two vdso modules. This could happen because the vdso module is
very special, and over the years, we have accumulated various ways to
load it.

In D10800, we added one mechanism for loading it, which took the form of
a generic load-from-memory capability. Unfortunately loading an elf file
from memory is not possible (because the loader never loads the entire
file), and our attempts to do so were causing crashes. So, in D34352, we
partially reverted D10800 and implemented a custom mechanism specific to
the vdso.

Unfortunately, enough of D10800 remained such that, under the right
circumstances, it could end up loading a second (non-functional) copy of
the vdso module. This happened when the process plugin did not support
the extended MemoryRegionInfo query (added in D22219, to workaround a
different bug), which meant that the loader plugin was not able to
recognise that the linux-vdso.so.1 module (this is how the loader calls
it) is in fact the same as the [vdso] module (the name used in
/proc/$PID/maps) we loaded before. This typically happened in a core
file, as they don't store this kind of information.

This patch fixes the issue by completing the revert of D10800 -- the
memory loading code is removed completely. It also reduces the scope of
the hackaround introduced in D22219 -- it isn't completely sound and is
only relevant for fairly old (but still supported) versions of android.

I added the memory loading logic to the wasm dynamic loader, which has
since appeared and is relying on this feature (it even has a test). As
far as I can tell loading wasm modules from memory is possible and
reliable. MachO memory loading is not affected by this patch, as it uses
a completely different code path.

Since the scenarios/patches I described came without test cases, I have
created two new gdb-client tests cases for them. They're not
particularly readable, but right now, this is the best way we can
simulate the behavior (bugs) of a particular dynamic linker.

[mgorny]

Well, I don't see anything wrong with it and it doesn't seem to cause any regressions on FreeBSD. I wouldn't call myself an expert on this though.

[clayborg]

We have seen this issue as well in linux, so thanks for fixing it. I never did any of the work on the posix dyld loader so I had been avoiding trying to fix this.

lldb/include/lldb/Target/DynamicLoader.h

public:
   /// On some systems (e.g. Darwin based systems), lldb will get notified by
   /// the dynamic loader before it itself finished initializing and it's not
   /// safe to call certain APIs or SPIs.
   virtual bool IsFullyInitialized() { return true; }
 
 protected:
   // Utility methods for derived classes
 
+  lldb::ModuleSP FindModuleViaTarget(const FileSpec &file);
+
   /// Checks to see if the target module has changed, updates the target
   /// accordingly and returns the target executable module.
   lldb::ModuleSP GetTargetExecutable();
 
   /// Updates the load address of every allocatable section in \p module.
   ///
   /// \param module The module to traverse.
   ///

lldb/packages/Python/lldbsuite/test/gdbclientutils.py

 
 def hex_decode_bytes(hex_bytes):
     """
     Decode the hex string into a binary message by converting each two-character
     hex string into a single output byte.
     """
     out = ""
     hex_len = len(hex_bytes)
+    i = 0
     while i < hex_len - 1:
-        out += chr(int(hex_bytes[i:i + 2]), 16)
+        out += chr(int(hex_bytes[i:i + 2], 16))
         i += 2
     return out
 
 
 class MockGDBServerResponder:
     """
     A base class for handling client packets and issuing server responses for
     GDB tests.
def respond(self, packet):
         if packet == "qQueryGDBServer":
             return self.qQueryGDBServer()
         if packet == "qHostInfo":
             return self.qHostInfo()
         if packet == "qGetWorkingDir":
             return self.qGetWorkingDir()
         if packet == "qOffsets":
             return self.qOffsets();
+        if packet == "qProcessInfo":
+            return self.qProcessInfo()
         if packet == "qsProcessInfo":
             return self.qsProcessInfo()
         if packet.startswith("qfProcessInfo"):
             return self.qfProcessInfo(packet)
         if packet.startswith("qPathComplete:"):
             return self.qPathComplete()
         if packet.startswith("vFile:"):
             return self.vFile(packet)
def qfProcessInfo(self, packet):
         return "E04"
 
     def qGetWorkingDir(self):
         return "2f"
 
     def qOffsets(self):
         return ""
 
+    def qProcessInfo(self):
+        return ""
+
     def qHostInfo(self):
         return "ptrsize:8;endian:little;"
 
     def qQueryGDBServer(self):
         return "E04"
 
     def interrupt(self):
         raise self.UnexpectedPacketException()

lldb/source/Core/DynamicLoader.cpp

if (module) {
     ObjectFile *obj_file = module->GetObjectFile();
     if (obj_file != nullptr) {
       sections = obj_file->GetSectionList();
     }
   }
   return sections;
 }
 
-ModuleSP DynamicLoader::LoadModuleAtAddress(const FileSpec &file,
-                                            addr_t link_map_addr,
-                                            addr_t base_addr,
-                                            bool base_addr_is_offset) {
+ModuleSP DynamicLoader::FindModuleViaTarget(const FileSpec &file) {
   Target &target = m_process->GetTarget();
-  ModuleList &modules = target.GetImages();
   ModuleSpec module_spec(file, target.GetArchitecture());
-  ModuleSP module_sp;
 
-  if ((module_sp = modules.FindFirstModule(module_spec))) {
-    UpdateLoadedSections(module_sp, link_map_addr, base_addr,
-                         base_addr_is_offset);
+  if (ModuleSP module_sp = target.GetImages().FindFirstModule(module_spec))
     return module_sp;
-  }
 
-  if ((module_sp = target.GetOrCreateModule(module_spec, 
-                                            true /* notify */))) {
-    UpdateLoadedSections(module_sp, link_map_addr, base_addr,
-                         base_addr_is_offset);
+  if (ModuleSP module_sp = target.GetOrCreateModule(module_spec,
+                                                    /*notify=*/true))
     return module_sp;
-  }
-
-  bool check_alternative_file_name = true;
-  if (base_addr_is_offset) {
-    // Try to fetch the load address of the file from the process as we need
-    // absolute load address to read the file out of the memory instead of a
-    // load bias.
-    bool is_loaded = false;
-    lldb::addr_t load_addr;
-    Status error = m_process->GetFileLoadAddress(file, is_loaded, load_addr);
-    if (error.Success() && is_loaded) {
-      check_alternative_file_name = false;
-      base_addr = load_addr;
-    }
-  }
-
-  // We failed to find the module based on its name. Lets try to check if we
-  // can find a different name based on the memory region info.
-  if (check_alternative_file_name) {
-    MemoryRegionInfo memory_info;
-    Status error = m_process->GetMemoryRegionInfo(base_addr, memory_info);
-    if (error.Success() && memory_info.GetMapped() &&
-        memory_info.GetRange().GetRangeBase() == base_addr && 
-        !(memory_info.GetName().IsEmpty())) {
-      ModuleSpec new_module_spec(FileSpec(memory_info.GetName().GetStringRef()),
-                                 target.GetArchitecture());
 
-      if ((module_sp = modules.FindFirstModule(new_module_spec))) {
-        UpdateLoadedSections(module_sp, link_map_addr, base_addr, false);
-        return module_sp;
-      }
+  return nullptr;
 
-      if ((module_sp = target.GetOrCreateModule(new_module_spec, 
-                                                true /* notify */))) {
-        UpdateLoadedSections(module_sp, link_map_addr, base_addr, false);
-        return module_sp;
-      }
-    }
-  }
+ModuleSP DynamicLoader::LoadModuleAtAddress(const FileSpec &file,
+                                            addr_t link_map_addr,
+                                            addr_t base_addr,
+                                            bool base_addr_is_offset) {
+  if (ModuleSP module_sp = FindModuleViaTarget(file)) {
+    UpdateLoadedSections(module_sp, link_map_addr, base_addr,
+                         base_addr_is_offset);
 
-  if ((module_sp = m_process->ReadModuleFromMemory(file, base_addr))) {
-    UpdateLoadedSections(module_sp, link_map_addr, base_addr, false);
-    target.GetImages().AppendIfNeeded(module_sp);
-  }
-
-  return module_sp;
+  return nullptr;
 }
 
 int64_t DynamicLoader::ReadUnsignedIntWithSizeInBytes(addr_t addr,
                                                       int size_in_bytes) {
   Status error;
   uint64_t value =
       m_process->ReadUnsignedIntegerFromMemory(addr, size_in_bytes, 0, error);
   if (error.Fail())

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h

public:
 
   lldb::addr_t GetThreadLocalData(const lldb::ModuleSP module,
                                   const lldb::ThreadSP thread,
                                   lldb::addr_t tls_file_addr) override;
 
   // PluginInterface protocol
   llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }
 
+  lldb::ModuleSP LoadModuleAtAddress(const lldb_private::FileSpec &file,
+                                     lldb::addr_t link_map_addr,
+                                     lldb::addr_t base_addr,
+                                     bool base_addr_is_offset) override;
+
 protected:
   /// Runtime linker rendezvous structure.
   DYLDRendezvous m_rendezvous;
 
   /// Virtual load address of the inferior process.
   lldb::addr_t m_load_offset;
 
   /// Virtual entry address of the inferior process.

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp

if (ModuleSP module_sp = target.GetOrCreateModule(module_spec,
     UpdateLoadedSections(module_sp, LLDB_INVALID_ADDRESS, m_interpreter_base,
                          false);
     m_interpreter_module = module_sp;
     return module_sp;
   }
   return nullptr;
 }
 
+ModuleSP DynamicLoaderPOSIXDYLD::LoadModuleAtAddress(const FileSpec &file,
+                                                     addr_t link_map_addr,
+                                                     addr_t base_addr,
+                                                     bool base_addr_is_offset) {
+  if (ModuleSP module_sp = DynamicLoader::LoadModuleAtAddress(
+          file, link_map_addr, base_addr, base_addr_is_offset))
+    return module_sp;
+
+  // This works around an dynamic linker "bug" on android <= 23, where the
+  // dynamic linker would report the application name
+  // (e.g. com.example.myapplication) instead of the main process binary
+  // (/system/bin/app_process(32)). The logic is not sound in general (it
+  // assumes base_addr is the real address, even though it actually is a load
+  // bias), but it happens to work on adroid because app_process has a file
+  // address of zero.
+  // This should be removed after we drop support for android-23.
+  if (m_process->GetTarget().GetArchitecture().GetTriple().isAndroid()) {
+    MemoryRegionInfo memory_info;
+    Status error = m_process->GetMemoryRegionInfo(base_addr, memory_info);
+    if (error.Success() && memory_info.GetMapped() &&
+        memory_info.GetRange().GetRangeBase() == base_addr &&
+        !(memory_info.GetName().IsEmpty())) {
+      if (ModuleSP module_sp = DynamicLoader::LoadModuleAtAddress(
+              FileSpec(memory_info.GetName().GetStringRef()), link_map_addr,
+              base_addr, base_addr_is_offset))
+        return module_sp;
+    }
+  }
+
+  return nullptr;
+}
+
 void DynamicLoaderPOSIXDYLD::LoadAllCurrentModules() {
   DYLDRendezvous::iterator I;
   DYLDRendezvous::iterator E;
   ModuleList module_list;
   Log *log = GetLog(LLDBLog::DynamicLoader);
 
   LoadVDSO();
 

lldb/source/Plugins/DynamicLoader/wasm-DYLD/DynamicLoaderWasmDYLD.h

public:
 
   /// DynamicLoader
   /// \{
   void DidAttach() override;
   void DidLaunch() override {}
   Status CanLoadImage() override { return Status(); }
   lldb::ThreadPlanSP GetStepThroughTrampolinePlan(Thread &thread,
                                                   bool stop) override;
+  lldb::ModuleSP LoadModuleAtAddress(const lldb_private::FileSpec &file,
+                                     lldb::addr_t link_map_addr,
+                                     lldb::addr_t base_addr,
+                                     bool base_addr_is_offset) override;
+
   /// \}
 
   /// PluginInterface protocol.
   /// \{
   llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }
   /// \}
 };
 
 } // namespace wasm
 } // namespace lldb_private
 
 #endif // liblldb_Plugins_DynamicLoaderWasmDYLD_h_

lldb/source/Plugins/DynamicLoader/wasm-DYLD/DynamicLoaderWasmDYLD.cpp

void DynamicLoaderWasmDYLD::DidAttach() {
   auto error = m_process->LoadModules();
   LLDB_LOG_ERROR(log, std::move(error), "Couldn't load modules: {0}");
 }
 
 ThreadPlanSP DynamicLoaderWasmDYLD::GetStepThroughTrampolinePlan(Thread &thread,
                                                                  bool stop) {
   return ThreadPlanSP();
 }
+
+lldb::ModuleSP DynamicLoaderWasmDYLD::LoadModuleAtAddress(
+    const lldb_private::FileSpec &file, lldb::addr_t link_map_addr,
+    lldb::addr_t base_addr, bool base_addr_is_offset) {
+  if (ModuleSP module_sp = DynamicLoader::LoadModuleAtAddress(
+          file, link_map_addr, base_addr, base_addr_is_offset))
+    return module_sp;
+
+  if (ModuleSP module_sp = m_process->ReadModuleFromMemory(file, base_addr)) {
+    UpdateLoadedSections(module_sp, link_map_addr, base_addr, false);
+    m_process->GetTarget().GetImages().AppendIfNeeded(module_sp);
+    return module_sp;
+  }
+
+  return nullptr;
+}

lldb/test/API/functionalities/gdb_remote_client/TestGdbClientModuleLoad.py

+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+from lldbsuite.test.gdbclientutils import *
+from lldbsuite.test.lldbgdbclient import GDBRemoteTestBase
+from lldbsuite.support import seven
+
+class MyResponder(MockGDBServerResponder):
+    """
+    A responder which simulates a process with a single shared library loaded.
+    Its parameters allow configuration of various properties of the library.
+    """
+
+    def __init__(self, testcase, triple, library_name, auxv_entry, region_info):
+        MockGDBServerResponder.__init__(self)
+        self.testcase = testcase
+        self._triple = triple
+        self._library_name = library_name
+        self._auxv_entry = auxv_entry
+        self._region_info = region_info
+
+    def qSupported(self, client_supported):
+        return (super().qSupported(client_supported) +
+            ";qXfer:auxv:read+;qXfer:libraries-svr4:read+")
+
+    def qXferRead(self, obj, annex, offset, length):
+        if obj == "features" and annex == "target.xml":
+            return """<?xml version="1.0"?>
+                <target version="1.0">
+                  <architecture>i386:x86-64</architecture>
+                  <feature name="org.gnu.gdb.i386.core">
+                    <reg name="rip" bitsize="64" regnum="0" type="code_ptr" group="general"/>
+                  </feature>
+                </target>""", False
+        elif obj == "auxv":
+            # 0x09 = AT_ENTRY, which lldb uses to compute the load bias of the
+            # main binary.
+            return hex_decode_bytes(self._auxv_entry +
+                "09000000000000000000ee000000000000000000000000000000000000000000"), False
+        elif obj == "libraries-svr4":
+            return """<?xml version="1.0"?>
+                <library-list-svr4 version="1.0">
+                  <library name="%s" lm="0xdeadbeef" l_addr="0xef0000" l_ld="0xdeadbeef"/>
+                </library-list-svr4>""" % self._library_name, False
+        else:
+            return None, False
+
+    def qfThreadInfo(self):
+        return "m47"
+
+    def qsThreadInfo(self):
+        return "l"
+
+    def qProcessInfo(self):
+        return "pid:47;ptrsize:8;endian:little;triple:%s;" % hex_encode_bytes(self._triple)
+
+    def setBreakpoint(self, packet):
+        return "OK"
+
+    def readMemory(self, addr, length):
+        if addr == 0xee1000:
+            return "00"*0x30 + "0020ee0000000000"
+        elif addr == 0xee2000:
+            return "01000000000000000030ee0000000000dead00000000000000000000000000000000000000000000"
+        elif addr == 0xef0000:
+            with open(self.testcase.getBuildArtifact("libmodule_load.so"), "rb") as f:
+                contents = f.read(-1)
+            return hex_encode_bytes(seven.bitcast_to_string(contents))
+        return ("baadf00d00"*1000)[0:length*2]
+
+    def qMemoryRegionInfo(self, addr):
+        if addr < 0xee0000:
+            return "start:0;size:ee0000;"
+        elif addr < 0xef0000:
+            return "start:ee0000;size:10000;"
+        elif addr < 0xf00000:
+            return "start:ef0000;size:1000;permissions:rx;" + self._region_info
+        else:
+            return "start:ef1000;size:ffffffffff10f000"
+
+class TestGdbClientModuleLoad(GDBRemoteTestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipIfXmlSupportMissing
+    def test_android_app_process(self):
+        """
+        This test simulates the scenario where the (android) dynamic linker
+        reports incorrect file name of the main executable. Lldb uses
+        qMemoryRegionInfo to get the correct value.
+        """
+        region_info = "name:%s;" % (
+                    hex_encode_bytes(self.getBuildArtifact("libmodule_load.so")))
+        self.server.responder = MyResponder(self, "x86_64-pc-linux-android",
+                "bogus-name", "", region_info)
+        self.yaml2obj("module_load.yaml", self.getBuildArtifact("libmodule_load.so"))
+        target = self.createTarget("module_load.yaml")
+
+        process = self.connect(target)
+        self.assertTrue(process.IsValid(), "Process is valid")
+
+        lldbutil.expect_state_changes(self, self.dbg.GetListener(), process,
+                [lldb.eStateStopped])
+
+        self.filecheck("image list", __file__, "-check-prefix=ANDROID")
+# ANDROID: [  0] {{.*}} 0x0000000000ee0000 {{.*}}module_load
+# ANDROID: [  1] {{.*}} 0x0000000000ef0000 {{.*}}libmodule_load.so
+
+    @skipIfXmlSupportMissing
+    def test_vdso(self):
+        """
+        This test checks vdso loading in the situation where the process does
+        not have memory region information about the vdso address. This can
+        happen in core files, as they don't store this data.
+        We want to check that the vdso is loaded exactly once.
+        """
+        # vdso address
+        AT_SYSINFO_EHDR = "21000000000000000000ef0000000000"
+        self.server.responder = MyResponder(self, "x86_64-pc-linux",
+                "linux-vdso.so.1", AT_SYSINFO_EHDR, "")
+        self.yaml2obj("module_load.yaml", self.getBuildArtifact("libmodule_load.so"))
+        target = self.createTarget("module_load.yaml")
+
+        process = self.connect(target)
+        self.assertTrue(process.IsValid(), "Process is valid")
+
+        lldbutil.expect_state_changes(self, self.dbg.GetListener(), process,
+                [lldb.eStateStopped])
+
+        self.filecheck("image list", __file__, "-check-prefix=VDSO")
+# VDSO: [  0] {{.*}} 0x0000000000ee0000 {{.*}}module_load
+# VDSO: [  1] {{.*}} 0x0000000000ef0000 {{.*}}[vdso]
+        self.assertEquals(self.target().GetNumModules(), 2)

lldb/test/API/functionalities/gdb_remote_client/TestWasm.py

class MyResponder(MockGDBServerResponder):
     current_pc = load_address + 0x0a
 
     def __init__(self, obj_path, module_name = ""):
         self._obj_path = obj_path
         self._module_name = module_name or obj_path
         MockGDBServerResponder.__init__(self)
 
     def respond(self, packet):
-        if packet == "qProcessInfo":
-            return self.qProcessInfo()
         if packet[0:13] == "qRegisterInfo":
             return self.qRegisterInfo(packet[13:])
         return MockGDBServerResponder.respond(self, packet)
 
     def qSupported(self, client_supported):
         return "qXfer:libraries:read+;PacketSize=1000;vContSupported-"
 
     def qHostInfo(self):

lldb/test/API/functionalities/gdb_remote_client/module_load.yaml

+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x0000
+    AddressAlign:    0x4
+    Content:         "c3c3c3c3"
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x1000
+    AddressAlign:    0x4
+    Size:            0x28
+  - Name:            .dynamic
+    Type:            SHT_DYNAMIC
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x8
+    Entries:
+      - Tag:             DT_DEBUG
+        Value:           0xdead0000
+
+ProgramHeaders:
+  - Type: PT_LOAD
+    Flags: [ PF_X, PF_R ]
+    VAddr: 0x0000
+    Align: 0x4
+    FirstSec: .text
+    LastSec:  .text
+  - Type: PT_LOAD
+    Flags: [ PF_R, PF_W ]
+    VAddr: 0x1000
+    Align: 0x4
+    FirstSec: .data
+    LastSec:  .dynamic
+  - Type:            PT_DYNAMIC
+    Flags:           [ PF_W, PF_R ]
+    VAddr:           0x1028
+    FirstSec:        .dynamic
+    LastSec:         .dynamic
+DynamicSymbols:
+  - Name:            _r_debug
+    Type:            STT_OBJECT
+    Section:         .data
+    Binding:         STB_GLOBAL
+    Value:           0x0
+    Size:            0x28
+