[intel-pt] Fix existing support in LLDB

[wallace]

Summary

https://reviews.llvm.org/D33035 added in 2017 basic support for intel-pt. I plan to improve it and use it to support reverse debugging.

I fixed a couple of issues and now this plugin works again:

1. pythonlib needed to be linked against it for the SB framework. Linking was failing because of this
2. the decoding functionality was broken because it lacked handling for instruction events. It seems old versions of libipt, the actual decoding library, didn't require these, but modern version require it (you can read more here https://github.com/intel/libipt/blob/master/doc/howto_libipt.md). These events signal overflows of the internal PT buffer in the CPU, enable/disable events of tracing, async cpu events, interrupts, etc.

I ended up refactoring a little bit the code to reduce code duplication.

In another diff I'll implement some basic tests.

This is a simple execution of the library:

(lldb) target create "/data/users/wallace/rr-project/a.out"
Current executable set to '/data/users/wallace/rr-project/a.out' (x86_64).
(lldb) plugin load liblldbIntelFeatures.so
(lldb) b main
Breakpoint 1: where = a.out`main + 8 at test.cpp:10, address = 0x00000000004007fa
(lldb) b test.cpp:14
Breakpoint 2: where = a.out`main + 50 at test.cpp:14, address = 0x0000000000400824
(lldb) r
Process 902754 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x00000000004007fa a.out`main at test.cpp:10
   7    }
   8   
   9    int main() {
-> 10     int z = 0;
   11     for(int i = 0; i < 10000; i++)
   12       z += fun(z);
   13  

Process 902754 launched: '/data/users/wallace/rr-project/a.out' (x86_64)
(lldb) processor-trace start all
(lldb) c
Process 902754 resuming
Process 902754 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 2.1
    frame #0: 0x0000000000400824 a.out`main at test.cpp:14
   11     for(int i = 0; i < 10000; i++)
   12       z += fun(z);
   13  
-> 14     cout << z<< endl;
   15     return 0;
   16   }

(lldb) processor-trace show-instr-log
thread #1: tid=902754
    0x7ffff72299b9 <+9>: addq   $0x8, %rsp
    0x7ffff72299bd <+13>: retq   
    0x4007ed <+16>: addl   $0x1, %eax
    0x4007f0 <+19>: leave  
    0x4007f1 <+20>: retq   
    0x400814 <+34>: addl   %eax, -0x4(%rbp)
    0x400817 <+37>: addl   $0x1, -0x8(%rbp)
    0x40081b <+41>: cmpl   $0x270f, -0x8(%rbp)       ; imm = 0x270F 
    0x400822 <+48>: jle    0x40080a                  ; <+24> at test.cpp:12
    0x400822 <+48>: jle    0x40080a                  ; <+24> at test.cpp:12

[clayborg]

Looks fine to me, but the original author should probably approve this

[wallace]

update commit message

[wallace]

His last activity was in Jun 2017. I hope he's still around.

[wallace]

merge the commits of this diff

lldb/tools/intel-features/CMakeLists.txt

set_source_files_properties(cli-wrapper.cpp PROPERTIES
                             COMPILE_FLAGS ${CLI_WRAPPER_PREPROCESSORS})
 
 add_lldb_library(lldbIntelFeatures SHARED
   cli-wrapper.cpp
   ${LLDB_INTEL_FEATURES_PYTHON_WRAP}
 
   LINK_LIBS
     ${FEATURE_LIBS}
+    ${PYTHON_LIBRARY}
   )
 
 # Add link dependencies for python wrapper
 if (LLDB_ENABLE_PYTHON AND LLDB_BUILD_INTEL_PT)
   add_dependencies(lldbIntelFeatures intel-features-swig_wrapper)
 endif()
 
 install(TARGETS lldbIntelFeatures
   LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX})

lldb/tools/intel-features/intel-pt/Decoder.h

private:
   ///  - start trace decoding
   void InitializePTInstDecoder(
       struct pt_insn_decoder **decoder, struct pt_config *config,
       const CPUInfo &pt_cpu, Buffer &pt_buffer,
       const ReadExecuteSectionInfos &readExecuteSectionInfos,
       lldb::SBError &sberror) const;
   void DecodeTrace(struct pt_insn_decoder *decoder,
                    Instructions &instruction_list, lldb::SBError &sberror);
+  int HandlePTInstructionEvents(pt_insn_decoder *decoder, int errcode,
+                                Instructions &instruction_list,
+                                lldb::SBError &sberror);
+
+  int AppendErrorToInstructionList(int errcode, pt_insn_decoder *decoder,
+                                   Instructions &instruction_list,
+                                   lldb::SBError &sberror);
+
+  void AppendErrorWithOffsetToInstructionList(int errcode,
+                                              uint64_t decoder_offset,
+                                              Instructions &instruction_list,
+                                              lldb::SBError &sberror);
+
+  void AppendErrorWithoutOffsetToInstructionList(int errcode,
+                                                 Instructions &instruction_list,
+                                                 lldb::SBError &sberror);
 
   // Function to diagnose and indicate errors during raw trace decoding
   void Diagnose(struct pt_insn_decoder *decoder, int errcode,
                 lldb::SBError &sberror, const struct pt_insn *insn = nullptr);
 
   class ThreadTraceInfo {
   public:
     ThreadTraceInfo()

lldb/tools/intel-features/intel-pt/Decoder.cpp

if (errcode < 0) {
                                        "\"%s\"",
                                        pt_errstr(pt_errcode(errcode)));
       pt_insn_free_decoder(*decoder);
       return;
     }
   }
 }
 
+void Decoder::AppendErrorWithOffsetToInstructionList(
+    int errcode, uint64_t decoder_offset, Instructions &instruction_list,
+    lldb::SBError &sberror) {
+  sberror.SetErrorStringWithFormat(
+      "processor trace decoding library: \"%s\"  [decoder_offset] => "
+      "[0x%" PRIu64 "]",
+      pt_errstr(pt_errcode(errcode)), decoder_offset);
+  instruction_list.emplace_back(sberror.GetCString());
+}
+
+void Decoder::AppendErrorWithoutOffsetToInstructionList(
+    int errcode, Instructions &instruction_list, lldb::SBError &sberror) {
+  sberror.SetErrorStringWithFormat("processor trace decoding library: \"%s\"",
+                                   pt_errstr(pt_errcode(errcode)));
+  instruction_list.emplace_back(sberror.GetCString());
+}
+
+int Decoder::AppendErrorToInstructionList(int errcode, pt_insn_decoder *decoder,
+                                          Instructions &instruction_list,
+                                          lldb::SBError &sberror) {
+  uint64_t decoder_offset = 0;
+  int errcode_off = pt_insn_get_offset(decoder, &decoder_offset);
+  if (errcode_off < 0) {
+    AppendErrorWithoutOffsetToInstructionList(errcode, instruction_list,
+                                              sberror);
+    return errcode_off;
+  }
+  AppendErrorWithOffsetToInstructionList(errcode, decoder_offset,
+                                         instruction_list, sberror);
+  return 0;
+}
+
+int Decoder::HandlePTInstructionEvents(pt_insn_decoder *decoder, int errcode,
+                                       Instructions &instruction_list,
+                                       lldb::SBError &sberror) {
+  while (errcode & pts_event_pending) {
+    pt_event event;
+    errcode = pt_insn_event(decoder, &event, sizeof(event));
+    if (errcode < 0)
+      return errcode;
+
+    // The list of events are in
+    // https://github.com/intel/libipt/blob/master/doc/man/pt_qry_event.3.md
+    if (event.type == ptev_overflow) {
+      int append_errcode = AppendErrorToInstructionList(
+          errcode, decoder, instruction_list, sberror);
+      if (append_errcode < 0)
+        return append_errcode;
+    }
+    // Other events don't signal stream errors
+  }
+
+  return 0;
+}
+
 // Start actual decoding of raw trace
 void Decoder::DecodeTrace(struct pt_insn_decoder *decoder,
                           Instructions &instruction_list,
                           lldb::SBError &sberror) {
   uint64_t decoder_offset = 0;
 
   while (1) {
     struct pt_insn insn;
 
     // Try to sync the decoder. If it fails then get the decoder_offset and try
     // to sync again. If the new_decoder_offset is same as decoder_offset then
     // we will not succeed in syncing for any number of pt_insn_sync_forward()
     // operations. Return in that case. Else keep resyncing until either end of
     // trace stream is reached or pt_insn_sync_forward() passes.
     int errcode = pt_insn_sync_forward(decoder);
     if (errcode < 0) {
       if (errcode == -pte_eos)
         return;
 
       int errcode_off = pt_insn_get_offset(decoder, &decoder_offset);
       if (errcode_off < 0) {
-        sberror.SetErrorStringWithFormat(
-            "processor trace decoding library: \"%s\"",
-            pt_errstr(pt_errcode(errcode)));
-        instruction_list.emplace_back(sberror.GetCString());
+        AppendErrorWithoutOffsetToInstructionList(errcode, instruction_list,
+                                                  sberror);
         return;
       }
 
       sberror.SetErrorStringWithFormat(
           "processor trace decoding library: \"%s\"  [decoder_offset] => "
           "[0x%" PRIu64 "]",
           pt_errstr(pt_errcode(errcode)), decoder_offset);
       instruction_list.emplace_back(sberror.GetCString());
if (errcode < 0) {
           instruction_list.emplace_back(sberror.GetCString());
           return;
         } else if (new_decoder_offset <= decoder_offset) {
           // We tried resyncing the decoder and decoder didn't make any
           // progress because the offset didn't change. We will not make any
           // progress further. Hence, returning in this situation.
           return;
         }
-        sberror.SetErrorStringWithFormat(
-            "processor trace decoding library: \"%s\"  [decoder_offset] => "
-            "[0x%" PRIu64 "]",
-            pt_errstr(pt_errcode(errcode)), new_decoder_offset);
-        instruction_list.emplace_back(sberror.GetCString());
+        AppendErrorWithOffsetToInstructionList(errcode, new_decoder_offset,
+                                               instruction_list, sberror);
         decoder_offset = new_decoder_offset;
       }
     }
 
     while (1) {
+      errcode = HandlePTInstructionEvents(decoder, errcode, instruction_list,
+                                          sberror);
+      if (errcode < 0) {
+        int append_errcode = AppendErrorToInstructionList(
+            errcode, decoder, instruction_list, sberror);
+        if (append_errcode < 0)
+          return;
+        break;
+      }
       errcode = pt_insn_next(decoder, &insn, sizeof(insn));
       if (errcode < 0) {
         if (insn.iclass == ptic_error)
           break;
 
         instruction_list.emplace_back(insn);
 
         if (errcode == -pte_eos)