[all-commits] [llvm/llvm-project] 128c0d: [intel-pt] Fix existing support in LLDB

[walter erquinigo via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 128c0d037d32c929c58d63fd7f324038430f73ba
      https://github.com/llvm/llvm-project/commit/128c0d037d32c929c58d63fd7f324038430f73ba
  Author: Walter Erquinigo <wallace at fb.com>
  Date:   2020-03-31 (Tue, 31 Mar 2020)

  Changed paths:
    M lldb/tools/intel-features/CMakeLists.txt
    M lldb/tools/intel-features/intel-pt/Decoder.cpp
    M lldb/tools/intel-features/intel-pt/Decoder.h

  Log Message:
  -----------
  [intel-pt] Fix existing support in LLDB

Summary:
//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
```

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D76872