2 files changed, 41 insertions, 27 deletions

diff --git a/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp b/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
index c4880fa945b..bae481a031b 100644
--- a/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
+++ b/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
@@ -294,9 +294,11 @@ DynamicLoaderDarwinKernel::SearchForKernelNearPC(Process *process) {
     return LLDB_INVALID_ADDRESS;
   addr_t pc = thread->GetRegisterContext()->GetPC(LLDB_INVALID_ADDRESS);
 
+  int ptrsize = process->GetTarget().GetArchitecture().GetAddressByteSize();
+
   // The kernel is always loaded in high memory, if the top bit is zero,
   // this isn't a kernel.
-  if (process->GetTarget().GetArchitecture().GetAddressByteSize() == 8) {
+  if (ptrsize == 8) {
     if ((pc & (1ULL << 63)) == 0) {
       return LLDB_INVALID_ADDRESS;
     }
@@ -309,26 +311,26 @@ DynamicLoaderDarwinKernel::SearchForKernelNearPC(Process *process) {
   if (pc == LLDB_INVALID_ADDRESS)
     return LLDB_INVALID_ADDRESS;
 
-  // The kernel will load at at one megabyte boundary (0x100000), or at that
-  // boundary plus an offset of one page (0x1000) or two, or four (0x4000),
-  // depending on the device.
+  int pagesize = 0x4000;  // 16k pages on 64-bit targets
+  if (ptrsize == 4)
+    pagesize = 0x1000;    // 4k pages on 32-bit targets
 
-  // Round the current pc down to the nearest one megabyte boundary - the place
-  // where we will start searching.
-  addr_t addr = pc & ~0xfffff;
+  // The kernel will be loaded on a page boundary.
+  // Round the current pc down to the nearest page boundary.
+  addr_t addr = pc & ~(pagesize - 1ULL);
 
-  // Search backwards 32 megabytes, looking for the start of the kernel at each
-  // one-megabyte boundary.
-  for (int i = 0; i < 32; i++, addr -= 0x100000) {
-    // x86_64 kernels are at offset 0
-    if (CheckForKernelImageAtAddress(addr, process).IsValid())
+  // Search backwards for 32 megabytes, or first memory read error.
+  while (pc - addr < 32 * 0x100000) {
+    bool read_error;
+    if (CheckForKernelImageAtAddress(addr, process, &read_error).IsValid())
       return addr;
-    // 32-bit arm kernels are at offset 0x1000 (one 4k page)
-    if (CheckForKernelImageAtAddress(addr + 0x1000, process).IsValid())
-      return addr + 0x1000;
-    // 64-bit arm kernels are at offset 0x4000 (one 16k page)
-    if (CheckForKernelImageAtAddress(addr + 0x4000, process).IsValid())
-      return addr + 0x4000;
+
+    // Stop scanning on the first read error we encounter; we've walked
+    // past this executable block of memory.
+    if (read_error == true)
+      break;
+
+    addr -= pagesize;
   }
 
   return LLDB_INVALID_ADDRESS;
@@ -387,13 +389,19 @@ lldb::addr_t DynamicLoaderDarwinKernel::SearchForKernelViaExhaustiveSearch(
 //----------------------------------------------------------------------
 
 bool
-DynamicLoaderDarwinKernel::ReadMachHeader(addr_t addr, Process *process, llvm::MachO::mach_header &header) {
-  Status read_error;
+DynamicLoaderDarwinKernel::ReadMachHeader(addr_t addr, Process *process, llvm::MachO::mach_header &header,
+                                          bool *read_error) {
+  Status error;
+  if (read_error)
+    *read_error = false;
 
   // Read the mach header and see whether it looks like a kernel
-  if (process->DoReadMemory (addr, &header, sizeof(header), read_error) !=
-      sizeof(header))
+  if (process->DoReadMemory (addr, &header, sizeof(header), error) !=
+      sizeof(header)) {
+    if (read_error)
+      *read_error = true;
     return false;
+  }
 
   const uint32_t magicks[] = { llvm::MachO::MH_MAGIC_64, llvm::MachO::MH_MAGIC, llvm::MachO::MH_CIGAM, llvm::MachO::MH_CIGAM_64};
 
@@ -427,10 +435,14 @@ DynamicLoaderDarwinKernel::ReadMachHeader(addr_t addr, Process *process, llvm::M
 //----------------------------------------------------------------------
 lldb_private::UUID
 DynamicLoaderDarwinKernel::CheckForKernelImageAtAddress(lldb::addr_t addr,
-                                                        Process *process) {
+                                                        Process *process,
+                                                        bool *read_error) {
   Log *log(lldb_private::GetLogIfAnyCategoriesSet(LIBLLDB_LOG_DYNAMIC_LOADER));
-  if (addr == LLDB_INVALID_ADDRESS)
+  if (addr == LLDB_INVALID_ADDRESS) {
+    if (read_error)
+      *read_error = true;
     return UUID();
+  }
 
   if (log)
     log->Printf("DynamicLoaderDarwinKernel::CheckForKernelImageAtAddress: "
@@ -439,7 +451,7 @@ DynamicLoaderDarwinKernel::CheckForKernelImageAtAddress(lldb::addr_t addr,
 
   llvm::MachO::mach_header header;
 
-  if (!ReadMachHeader(addr, process, header))
+  if (!ReadMachHeader(addr, process, header, read_error))
     return UUID();
 
   // First try a quick test -- read the first 4 bytes and see if there is a
diff --git a/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.h b/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.h
index 894b5521433..edcecd141d3 100644
--- a/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.h
+++ b/lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.h
@@ -283,11 +283,13 @@ protected:
   SearchForKernelViaExhaustiveSearch(lldb_private::Process *process);
 
   static bool
-  ReadMachHeader(lldb::addr_t addr, lldb_private::Process *process, llvm::MachO::mach_header &mh);
+  ReadMachHeader(lldb::addr_t addr, lldb_private::Process *process, llvm::MachO::mach_header &mh,
+                 bool *read_error = nullptr);
 
   static lldb_private::UUID
   CheckForKernelImageAtAddress(lldb::addr_t addr,
-                               lldb_private::Process *process);
+                               lldb_private::Process *process,
+                               bool *read_error = nullptr);
 
   lldb::addr_t m_kernel_load_address;
   KextImageInfo m_kernel; // Info about the current kernel image being used