[LLDB][Minidumps] Read x64 registers as 64b and handle truncation in the file builder

[Jlalond]

This patch addresses a bug where cs/fs and other segmentation flags were being identified as having a type of 32b and 64b for rflags. In that case the register value was returning the fail value 0xF... and this was corrupting some minidumps. Here we just read it as a 64b value and truncate it.

In addition to that fix, I added comparing the registers from the live process to the loaded core for the generic minidump test. Prior only being ARM register tests. This explains why this was not detected before.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Jacob Lalonde (Jlalond)

Changes

This patch addresses a bug where cs/gs and other segmentation flags were being identified as having a type of 32b and 64b for rflags. In that case the register value was returning the fail value 0xF... and this was corrupting some minidumps. Here we just read it as a 64b value and truncate it.

In addition to that fix, I added comparing the registers from the live process to the loaded core for the generic minidump test. Prior only being ARM register tests. This explains why this was not detected before.

---

Full diff: https://github.com/llvm/llvm-project/pull/106473.diff

2 Files Affected:

• (modified) lldb/source/Plugins/ObjectFile/Minidump/MinidumpFileBuilder.cpp (+8-6)
• (modified) lldb/test/API/functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py (+25-1)

diff --git a/lldb/source/Plugins/ObjectFile/Minidump/MinidumpFileBuilder.cpp b/lldb/source/Plugins/ObjectFile/Minidump/MinidumpFileBuilder.cpp
index 689a3fb0e84852..13355afb58dbd1 100644
--- a/lldb/source/Plugins/ObjectFile/Minidump/MinidumpFileBuilder.cpp
+++ b/lldb/source/Plugins/ObjectFile/Minidump/MinidumpFileBuilder.cpp
@@ -491,12 +491,14 @@ GetThreadContext_x86_64(RegisterContext *reg_ctx) {
   thread_context.r14 = read_register_u64(reg_ctx, "r14");
   thread_context.r15 = read_register_u64(reg_ctx, "r15");
   thread_context.rip = read_register_u64(reg_ctx, "rip");
-  thread_context.eflags = read_register_u32(reg_ctx, "rflags");
-  thread_context.cs = read_register_u16(reg_ctx, "cs");
-  thread_context.fs = read_register_u16(reg_ctx, "fs");
-  thread_context.gs = read_register_u16(reg_ctx, "gs");
-  thread_context.ss = read_register_u16(reg_ctx, "ss");
-  thread_context.ds = read_register_u16(reg_ctx, "ds");
+  // To make our code agnostic to whatever type the register value identifies
+  // itself as, we read as a u64 and truncate to u32/u16 ourselves.
+  thread_context.eflags = read_register_u64(reg_ctx, "rflags");
+  thread_context.cs = read_register_u64(reg_ctx, "cs");
+  thread_context.fs = read_register_u64(reg_ctx, "fs");
+  thread_context.gs = read_register_u64(reg_ctx, "gs");
+  thread_context.ss = read_register_u64(reg_ctx, "ss");
+  thread_context.ds = read_register_u64(reg_ctx, "ds");
   return thread_context;
 }
 
diff --git a/lldb/test/API/functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py b/lldb/test/API/functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py
index 5abaa05a90f63e..81b0e44146a44e 100644
--- a/lldb/test/API/functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py
+++ b/lldb/test/API/functionalities/process_save_core_minidump/TestProcessSaveCoreMinidump.py
@@ -17,6 +17,7 @@ def verify_core_file(
         expected_modules,
         expected_threads,
         stacks_to_sps_map,
+        stacks_to_registers_map,
     ):
         # To verify, we'll launch with the mini dump
         target = self.dbg.CreateTarget(None)
@@ -62,6 +63,12 @@ def verify_core_file(
             # Try to read just past the red zone and fail
             process.ReadMemory(sp - red_zone - 1, 1, error)
             self.assertTrue(error.Fail(), "No failure when reading past the red zone")
+            # Verify the registers are the same
+            self.assertTrue(thread_id, stacks_to_registers_map)
+            register_val_list = stacks_to_registers_map[thread_id]
+            frame_register_list = frame.GetRegisters()
+            for x in register_val_list:
+                self.assertEqual(x.GetValueAsUnsigned(), frame_register_list.GetFirstValueByName(x.GetName()).GetValueAsUnsigned())
 
         self.dbg.DeleteTarget(target)
 
@@ -93,12 +100,14 @@ def test_save_linux_mini_dump(self):
             expected_number_of_threads = process.GetNumThreads()
             expected_threads = []
             stacks_to_sp_map = {}
+            stakcs_to_registers_map = {}
 
             for thread_idx in range(process.GetNumThreads()):
                 thread = process.GetThreadAtIndex(thread_idx)
                 thread_id = thread.GetThreadID()
                 expected_threads.append(thread_id)
                 stacks_to_sp_map[thread_id] = thread.GetFrameAtIndex(0).GetSP()
+                stakcs_to_registers_map[thread_id] = thread.GetFrameAtIndex(0).GetRegisters()
 
             # save core and, kill process and verify corefile existence
             base_command = "process save-core --plugin-name=minidump "
@@ -110,6 +119,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             self.runCmd(base_command + " --style=modified-memory '%s'" % (core_dirty))
@@ -120,6 +130,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             self.runCmd(base_command + " --style=full '%s'" % (core_full))
@@ -130,6 +141,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             options = lldb.SBSaveCoreOptions()
@@ -147,6 +159,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             options = lldb.SBSaveCoreOptions()
@@ -163,6 +176,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             # Minidump can now save full core files, but they will be huge and
@@ -181,6 +195,7 @@ def test_save_linux_mini_dump(self):
                 expected_modules,
                 expected_threads,
                 stacks_to_sp_map,
+                stakcs_to_registers_map
             )
 
             self.assertSuccess(process.Kill())
@@ -276,12 +291,14 @@ def test_save_linux_mini_dump_default_options(self):
             expected_threads = []
             stacks_to_sp_map = {}
             expected_pid = process.GetProcessInfo().GetProcessID()
+            stacks_to_registers_map = {}
 
             for thread_idx in range(process.GetNumThreads()):
                 thread = process.GetThreadAtIndex(thread_idx)
                 thread_id = thread.GetThreadID()
                 expected_threads.append(thread_id)
                 stacks_to_sp_map[thread_id] = thread.GetFrameAtIndex(0).GetSP()
+                stacks_to_registers_map[thread_id] = thread.GetFrameAtIndex(0).GetRegisters()
 
 
             # This is almost identical to the single thread test case because
@@ -294,7 +311,14 @@ def test_save_linux_mini_dump_default_options(self):
             error = process.SaveCore(options)
             self.assertTrue(error.Success())
 
-            self.verify_core_file(default_value_file, expected_pid, expected_modules, expected_threads, stacks_to_sp_map)
+            self.verify_core_file(
+                default_value_file,
+                expected_pid,
+                expected_modules,
+                expected_threads,
+                stacks_to_sp_map,
+                stacks_to_registers_map
+            )
 
         finally:
             self.assertTrue(self.dbg.DeleteTarget(target))

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.