[lldb] Don't call AddRemoteRegisters if the target XML did not include any registers (llvm#96907)

Fixes llvm#92541

When e69a3d1 added fallback register
layouts, it assumed that the choices were target XML with registers, or
no target XML at all.

In the linked issue, a user has a debug stub that does have target XML,
but it's missing register information.

This caused us to finalize the register information using an empty set
of registers got from target XML, then fail an assert when we attempted
to add the fallback set. Since we think we've already completed the
register information.

This change adds a check to prevent that first call and expands the
existing tests to check each architecture without target XML and with
target XML missing register information.

Author: DavidSpickett

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

@@ -4879,7 +4879,9 @@ bool ProcessGDBRemote::GetGDBServerRegisterInfo(ArchSpec &arch_to_use) {
   m_registers_enum_types.clear();
   std::vector<DynamicRegisterInfo::Register> registers;
   if (GetGDBServerRegisterInfoXMLAndProcess(arch_to_use, "target.xml",
-                                            registers))
+                                            registers) &&
+      // Target XML is not required to include register information.
+      !registers.empty())
     AddRemoteRegisters(registers, arch_to_use);
 
   return m_register_info_sp->GetNumRegisters() > 0;

lldb/test/API/functionalities/gdb_remote_client/TestGDBServerNoTargetXML.py renamed to lldb/test/API/functionalities/gdb_remote_client/TestGDBServerNoTargetXMLRegisters.py

@@ -1,6 +1,6 @@
 """
 Check that lldb falls back to default register layouts when the remote provides
-no target XML.
+no target XML or does not include registers in the target XML.
 
 GPRS are passed to the responder to create register data to send back to lldb.
 Registers in SUPPL are virtual registers based on those general ones. The tests
@@ -14,6 +14,8 @@
 from lldbsuite.test.lldbgdbclient import GDBRemoteTestBase
 
 import binascii
+from textwrap import dedent
+
 
 class MyResponder(MockGDBServerResponder):
     @staticmethod
@@ -22,8 +24,10 @@ def filecheck_to_blob(fc):
             val = l.split("0x")[1]
             yield binascii.b2a_hex(bytes(reversed(binascii.a2b_hex(val)))).decode()
 
-    def __init__(self, reg_data, halt_reason):
+    def __init__(self, architecture, has_target_xml, reg_data, halt_reason):
         super().__init__()
+        self.architecture = architecture
+        self.has_target_xml = has_target_xml
         self.reg_data = "".join(self.filecheck_to_blob(reg_data))
         self.halt_reason = halt_reason
 
@@ -36,13 +40,24 @@ def readRegisters(self):
     def haltReason(self):
         return self.halt_reason
 
+    def qXferRead(self, obj, annex, offset, length):
+        if self.has_target_xml and annex == "target.xml":
+            return (
+                dedent(
+                    f"""\
+                    <?xml version="1.0"?>
+                    <target version="1.0">
+                      <architecture>{self.architecture}</architecture>
+                    </target>"""
+                ),
+                False,
+            )
+
+        return None, False
 
-class TestGDBServerTargetXML(GDBRemoteTestBase):
-    @skipIfRemote
-    @skipIfLLVMTargetMissing("X86")
-    def test_x86_64_regs(self):
-        """Test grabbing various x86_64 registers from gdbserver."""
 
+class TestGDBServerTargetXML(GDBRemoteTestBase):
+    def check_x86_64_regs(self, has_target_xml):
         GPRS = """
 CHECK-AMD64-DAG: rax = 0x0807060504030201
 CHECK-AMD64-DAG: rbx = 0x1817161514131211
@@ -125,6 +140,8 @@ def test_x86_64_regs(self):
 """
 
         self.server.responder = MyResponder(
+            "x86-64",
+            has_target_xml,
             GPRS,
             "T02thread:1ff0d;threads:1ff0d;thread-pcs:000000010001bc00;07:0102030405060708;10:1112131415161718;",
         )
@@ -155,10 +172,21 @@ def test_x86_64_regs(self):
         self.match("register read flags", ["eflags = 0x1c1b1a19"])
 
     @skipIfRemote
-    @skipIfLLVMTargetMissing("AArch64")
-    def test_aarch64_regs(self):
-        """Test grabbing various aarch64 registers from gdbserver."""
+    @skipIfLLVMTargetMissing("X86")
+    def test_x86_64_regs_no_target_xml(self):
+        """Test grabbing various x86_64 registers from gdbserver when there
+        is no target XML."""
+        self.check_x86_64_regs(False)
+
+    @skipIfXmlSupportMissing
+    @skipIfRemote
+    @skipIfLLVMTargetMissing("X86")
+    def test_x86_64_regs_no_register_info(self):
+        """Test grabbing various x86_64 registers from gdbserver when there
+        is target XML but it does not include register info."""
+        self.check_x86_64_regs(True)
 
+    def check_aarch64_regs(self, has_target_xml):
         GPRS = """
 CHECK-AARCH64-DAG: x0 = 0x0001020304050607
 CHECK-AARCH64-DAG: x1 = 0x0102030405060708
@@ -232,6 +260,8 @@ def test_aarch64_regs(self):
 """
 
         self.server.responder = MyResponder(
+            "aarch64",
+            has_target_xml,
             GPRS,
             "T02thread:1ff0d;threads:1ff0d;thread-pcs:000000010001bc00;07:0102030405060708;10:1112131415161718;",
         )
@@ -258,10 +288,21 @@ def test_aarch64_regs(self):
         self.match("register read flags", ["cpsr = 0x21222324"])
 
     @skipIfRemote
-    @skipIfLLVMTargetMissing("X86")
-    def test_i386_regs(self):
-        """Test grabbing various i386 registers from gdbserver."""
+    @skipIfLLVMTargetMissing("AArch64")
+    def test_aarch64_regs_no_target_xml(self):
+        """Test grabbing various aarch64 registers from gdbserver when there
+        is no target XML."""
+        self.check_aarch64_regs(False)
+
+    @skipIfXmlSupportMissing
+    @skipIfRemote
+    @skipIfLLVMTargetMissing("AArch64")
+    def test_aarch64_regs_no_register_info(self):
+        """Test grabbing various aarch64 registers from gdbserver when there
+        is target XML but it does not include register info."""
+        self.check_aarch64_regs(True)
 
+    def check_i386_regs(self, has_target_xml):
         GPRS = """
 CHECK-I386-DAG: eax = 0x04030201
 CHECK-I386-DAG: ecx = 0x14131211
@@ -307,6 +348,8 @@ def test_i386_regs(self):
 """
 
         self.server.responder = MyResponder(
+            "i386",
+            has_target_xml,
             GPRS,
             "T02thread:1ff0d;threads:1ff0d;thread-pcs:000000010001bc00;07:0102030405060708;10:1112131415161718;",
         )
@@ -329,3 +372,18 @@ def test_i386_regs(self):
         self.match("register read sp", ["esp = 0x44434241"])
         self.match("register read pc", ["eip = 0x84838281"])
         self.match("register read flags", ["eflags = 0x94939291"])
+
+    @skipIfRemote
+    @skipIfLLVMTargetMissing("X86")
+    def test_i386_regs_no_target_xml(self):
+        """Test grabbing various i386 registers from gdbserver when there is
+        no target XML."""
+        self.check_i386_regs(False)
+
+    @skipIfXmlSupportMissing
+    @skipIfRemote
+    @skipIfLLVMTargetMissing("X86")
+    def test_i386_regs_no_register_info(self):
+        """Test grabbing various i386 registers from gdbserver when there is
+        target XML but it does not include register info."""
+        self.check_i386_regs(True)