This is an ongoing series of commits that are reformatting our Python
code. Reformatting is done with `black` (23.1.0).
If you end up having problems merging this commit because you have made
changes to a python file, the best way to handle that is to run `git
checkout --ours <yourfile>` and then reformat it with black.
RFC: https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style
Differential revision: https://reviews.llvm.org/D151460
These tests were being tested against a version of libipt from last
year. We just updated libipt to top of tree and many errors broke
because the new version of libipt emits more events than the older one,
which is fine.
`./bin/lldb-dotest -p TestTrace` passes
The per-PSB packet decoding logic was wrong because it was assuming that pt_insn_get_sync_offset was being udpated after every PSB. Silly me, that is not true. It returns the offset of the PSB packet after invoking pt_insn_sync_forward regardless of how many PSBs are visited later. Instead, I'm now following the approach described in https://github.com/intel/libipt/blob/master/doc/howto_libipt.md#parallel-decode for parallel decoding, which is basically what we need.
A nasty error that happened because of this is that when we had two PSBs (A and B), the following was happening
1. PSB A was processed all the way up to the end of the trace, which includes PSB B.
2. PSB B was then processed until the end of the trace.
The instructions emitted by step 2. were also emitted as part of step 1. so our trace had duplicated chunks. This problem becomes worse when you many PSBs.
As part of making sure this diff is correct, I added some other features that are very useful.
- Added a "synchronization point" event to the TraceCursor, so we can inspect when PSBs are emitted.
- Removed the single-thread decoder. Now the per-cpu decoder and single-thread decoder use the same code paths.
- Use the query decoder to fetch PSBs and timestamps. It turns out that the pt_insn_sync_forward of the instruction decoder can move past several PSBs (this means that we could skip some TSCs). On the other hand, the pt_query_sync_forward method doesn't skip PSBs, so we can get more accurate sync events and timing information.
- Turned LibiptDecoder into PSBBlockDecoder, which decodes single PSB blocks. It is the fundamental processing unit for decoding.
- Added many comments, asserts and improved error handling for clarity.
- Improved DecodeSystemWideTraceForThread so that a TSC is emitted always before a cpu change event. This was a bug that was annoying me before.
- SplitTraceInContinuousExecutions and FindLowestTSCInTrace are now using the query decoder, which can identify precisely each PSB along with their TSCs.
- Added an "only-events" option to the trace dumper to inspect only events.
I did extensive testing and I think we should have an in-house testing CI. The LLVM buildbots are not capable of supporting testing post-mortem traces of hundreds of megabytes. I'll leave that for later, but at least for now the current tests were able to catch most of the issues I encountered when doing this task.
A sample output of a program that I was single stepping is the following. You can see that only one PSB is emitted even though stepping happened!
```
thread #1: tid = 3578223
0: (event) trace synchronization point [offset = 0x0xef0]
a.out`main + 20 at main.cpp:29:20
1: 0x0000000000402479 leaq -0x1210(%rbp), %rax
2: (event) software disabled tracing
3: 0x0000000000402480 movq %rax, %rdi
4: (event) software disabled tracing
5: (event) software disabled tracing
6: 0x0000000000402483 callq 0x403bd4 ; std::vector<int, std::allocator<int>>::vector at stl_vector.h:391:7
7: (event) software disabled tracing
a.out`std::vector<int, std::allocator<int>>::vector() at stl_vector.h:391:7
8: 0x0000000000403bd4 pushq %rbp
9: (event) software disabled tracing
10: 0x0000000000403bd5 movq %rsp, %rbp
11: (event) software disabled tracing
```
This is another trace of a long program with a few PSBs.
```
(lldb) thread trace dump instructions -E -f thread #1: tid = 3603082
0: (event) trace synchronization point [offset = 0x0x80]
47417: (event) software disabled tracing
129231: (event) trace synchronization point [offset = 0x0x800]
146747: (event) software disabled tracing
246076: (event) software disabled tracing
259068: (event) trace synchronization point [offset = 0x0xf78]
259276: (event) software disabled tracing
259278: (event) software disabled tracing
no more data
```
Differential Revision: https://reviews.llvm.org/D131630
Thanks to fredzhou@fb.com for coming up with this feature.
When tracing in per-cpu mode, we have information of in which cpu we are execution each instruction, which comes from the context switch trace. This diff makes this information available as a `cpu changed event`, which an additional accessor in the cursor `GetCPU()`. As cpu changes are very infrequent, any consumer should listen to cpu change events instead of querying the actual cpu of a trace item. Once a cpu change event is seen, the consumer can invoke GetCPU() to get that information. Also, it's possible to invoke GetCPU() on an arbitrary instruction item, which will return the last cpu seen. However, this call is O(logn) and should be used sparingly.
Manually tested with a sample program that starts on cpu 52, then goes to 18, and then goes back to 52.
Differential Revision: https://reviews.llvm.org/D129340
We want to include events with metadata, like context switches, and this
requires the API to handle events with payloads (e.g. information about
such context switches). Besides this, we want to support multiple
similar events between two consecutive instructions, like multiple
context switches. However, the current implementation is not good for this because
we are defining events as bitmask enums associated with specific
instructions. Thus, we need to decouple instructions from events and
make events actual items in the trace, just like instructions and
errors.
- Add accessors in the TraceCursor to know if an item is an event or not
- Modify from the TraceDumper all the way to DecodedThread to support
- Renamed the paused event to disabled.
- Improved the tsc handling logic. I was using an API for getting the tsc from libipt, but that was an overkill that should be used when not processing events manually, but as we are already processing events, we can more easily get the tscs.
event items. Fortunately this simplified many things
- As part of this refactor, I also fixed and long stating issue, which is that some non decoding errors were being inserted in the decoded thread. I changed this so that TraceIntelPT::Decode returns an error if the decoder couldn't be set up proplerly. Then, errors within a trace are actual anomalies found in between instrutions.
All test pass
Differential Revision: https://reviews.llvm.org/D128576
Eliminate boilerplate of having each test manually assign to `mydir` by calling
`compute_mydir` in lldbtest.py.
Differential Revision: https://reviews.llvm.org/D128077
A trace might contain events traced during the target's execution. For
example, a thread might be paused for some period of time due to context
switches or breakpoints, which actually force a context switch. Not only
that, a trace might be paused because the CPU decides to trace only a
specific part of the target, like the address filtering provided by
intel pt, which will cause pause events. Besides this case, other kinds
of events might exist.
This patch adds the method `TraceCursor::GetEvents()`` that returns the
list of events that happened right before the instruction being pointed
at by the cursor. Some refactors were done to make this change simpler.
Besides this new API, the instruction dumper now supports the -e flag
which shows pause events, like in the following example, where pauses
happened due to breakpoints.
```
thread #1: tid = 2717361
a.out`main + 20 at main.cpp:27:20
0: 0x00000000004023d9 leaq -0x1200(%rbp), %rax
[paused]
1: 0x00000000004023e0 movq %rax, %rdi
[paused]
2: 0x00000000004023e3 callq 0x403a62 ; std::vector<int, std::allocator<int> >::vector at stl_vector.h:391:7
a.out`std::vector<int, std::allocator<int> >::vector() at stl_vector.h:391:7
3: 0x0000000000403a62 pushq %rbp
4: 0x0000000000403a63 movq %rsp, %rbp
```
The `dump info` command has also been updated and now it shows the
number of instructions that have associated events.
Differential Revision: https://reviews.llvm.org/D123982
Jonas Devlieghere