[lldb][AArch64] Add Guarded Control Stack support for Linux core files

This allows you to read the same registers as you would for a live process.

As the content of proc/pid/smaps is not included in the core file,
we don't get the "ss" marker. The GCS region is stil in the list
though.

Author: DavidSpickett

lldb/source/Plugins/Process/elf-core/RegisterContextPOSIXCore_arm64.cpp

@@ -69,6 +69,15 @@ RegisterContextCorePOSIX_arm64::Create(Thread &thread, const ArchSpec &arch,
   if (fpmr_data.GetByteSize() >= sizeof(uint64_t))
     opt_regsets.Set(RegisterInfoPOSIX_arm64::eRegsetMaskFPMR);
 
+  DataExtractor gcs_data = getRegset(notes, arch.GetTriple(), AARCH64_GCS_Desc);
+  struct __attribute__((packed)) gcs_regs {
+    uint64_t features_enabled;
+    uint64_t features_locked;
+    uint64_t gcspr_e0;
+  };
+  if (gcs_data.GetByteSize() >= sizeof(gcs_regs))
+    opt_regsets.Set(RegisterInfoPOSIX_arm64::eRegsetMaskGCS);
+
   auto register_info_up =
       std::make_unique<RegisterInfoPOSIX_arm64>(arch, opt_regsets);
   return std::unique_ptr<RegisterContextCorePOSIX_arm64>(
@@ -136,6 +145,9 @@ RegisterContextCorePOSIX_arm64::RegisterContextCorePOSIX_arm64(
   if (m_register_info_up->IsFPMRPresent())
     m_fpmr_data = getRegset(notes, target_triple, AARCH64_FPMR_Desc);
 
+  if (m_register_info_up->IsGCSPresent())
+    m_gcs_data = getRegset(notes, target_triple, AARCH64_GCS_Desc);
+
   ConfigureRegisterContext();
 }
 
@@ -330,6 +342,11 @@ bool RegisterContextCorePOSIX_arm64::ReadRegister(const RegisterInfo *reg_info,
     assert(offset < m_mte_data.GetByteSize());
     value.SetFromMemoryData(*reg_info, m_mte_data.GetDataStart() + offset,
                             reg_info->byte_size, lldb::eByteOrderLittle, error);
+  } else if (IsGCS(reg)) {
+    offset = reg_info->byte_offset - m_register_info_up->GetGCSOffset();
+    assert(offset < m_gcs_data.GetByteSize());
+    value.SetFromMemoryData(*reg_info, m_gcs_data.GetDataStart() + offset,
+                            reg_info->byte_size, lldb::eByteOrderLittle, error);
   } else if (IsSME(reg)) {
     // If you had SME in the process, active or otherwise, there will at least
     // be a ZA header. No header, no SME at all.

lldb/source/Plugins/Process/elf-core/RegisterContextPOSIXCore_arm64.h

@@ -63,6 +63,7 @@ class RegisterContextCorePOSIX_arm64 : public RegisterContextPOSIX_arm64 {
   lldb_private::DataExtractor m_mte_data;
   lldb_private::DataExtractor m_zt_data;
   lldb_private::DataExtractor m_fpmr_data;
+  lldb_private::DataExtractor m_gcs_data;
 
   SVEState m_sve_state = SVEState::Unknown;
   uint16_t m_sve_vector_length = 0;

lldb/source/Plugins/Process/elf-core/RegisterUtilities.h

@@ -148,6 +148,10 @@ constexpr RegsetDesc AARCH64_FPMR_Desc[] = {
     {llvm::Triple::Linux, llvm::Triple::aarch64, llvm::ELF::NT_ARM_FPMR},
 };
 
+constexpr RegsetDesc AARCH64_GCS_Desc[] = {
+    {llvm::Triple::Linux, llvm::Triple::aarch64, llvm::ELF::NT_ARM_GCS},
+};
+
 constexpr RegsetDesc PPC_VMX_Desc[] = {
     {llvm::Triple::FreeBSD, llvm::Triple::UnknownArch, llvm::ELF::NT_PPC_VMX},
     {llvm::Triple::Linux, llvm::Triple::UnknownArch, llvm::ELF::NT_PPC_VMX},

lldb/test/API/linux/aarch64/gcs/TestAArch64LinuxGCS.py

@@ -374,3 +374,35 @@ def test_gcs_expression_enable_gcs(self):
         # consistent with the disabled -> enabled behaviour.
         enabled |= 1
         self.check_gcs_registers(enabled, locked, spr_el0)
+
+    @skipIfLLVMTargetMissing("AArch64")
+    def test_gcs_core_file(self):
+        # To re-generate the core file, build the test file and run it on a
+        # machine with GCS enabled. Note that because the kernel decides where
+        # the GCS is stored, the value of gcspr_el0 and which memory region it
+        # points to may change between runs.
+
+        self.runCmd("target create --core corefile")
+
+        self.expect(
+            "bt",
+            substrs=["stop reason = SIGSEGV: control protection fault"],
+        )
+
+        self.expect(
+            "register read --all",
+            substrs=[
+                "Guarded Control Stack Registers:",
+                "gcs_features_enabled = 0x0000000000000001",
+                "gcs_features_locked = 0x0000000000000000",
+                "gcspr_el0 = 0x0000ffffa83ffff0",
+            ],
+        )
+
+        # Core files do not include /proc/pid/smaps, so we cannot see the
+        # shadow stack "ss" flag. gcspr_el0 should at least point to some mapped
+        # region.
+        self.expect(
+            "memory region $gcspr_el0",
+            substrs=["[0x0000ffffa8000000-0x0000ffffa8400000) rw-"],
+        )