When lldb stops to run a breakpoint condition or other callback that has
to happen between the private stop and returning control to the user, it
will run in the state where the public state is still "running". But if
the callback needs to run lldb commands or python code, it needs to see
the correct "stop" state.
We used to handle that by switching the public state to stopped before
running the callbacks. However, that opened a window where we are still
handling the stop event and another thread would be allowed to continue
the target or do other actions that can interfere with that orderly
process.
This patch adds the ability to designate a particular thread as "seeing
the private state" while all other threads see the "public state". Then
when we run a breakpoint callback, no threads but the one that is
actually running the callback will see the state change until the event
has been delivered to the primary state listener.
It also adds a test that while a long-running breakpoint callback runs,
another thread continues to see the state as running.
Prior to this patch, SBFrame/SBThread methods exhibit racy behavior if
called while the process is running, because they do not lock the
`Process::RetRunLock` mutex. If they did, they would fail, correctly
identifying that the process is not running.
Some methods _attempt_ to protect against this with the pattern:
```
ExecutionContext exe_ctx(m_opaque_sp.get(), lock); // this is a different lock
Process *process = exe_ctx.GetProcessPtr();
if (process) {
Process::StopLocker stop_locker;
if (stop_locker.TryLock(&process->GetRunLock()))
.... do work ...
```
However, this is also racy: the constructor of `ExecutionContext` will
access the frame list, which is something that can only be done once the
process is stopped.
With this patch:
1. The constructor of `ExecutionContext` now expects a `ProcessRunLock`
as an argument. It attempts to lock the run lock, and only fills in
information about frames and threads if the lock can be acquired.
Callers of the constructor are expected to check the lock.
2. All uses of ExecutionContext are adjusted to conform to the above.
3. The SBThread.cpp-defined helper function ResumeNewPlan now expects a
locked ProcessRunLock as _proof_ that the execution is stopped. It will
unlock the mutex prior to resuming the process.
This commit exposes many opportunities for early-returns, but these
would increase the diff of this patch and distract from the important
changes, so we opt not to do it here.
I am using VSCode with the official vscode-lldb extension. When I try to
list the breakpoints in the debug console get the message:
```
br list
can't evaluate expressions when the process is running.
```
I know that this is wrong and you need to use
```
`br list
(lldb) br list
No breakpoints currently set.
```
but the error message is misleading. I cleaned up the code and now the
error message is
```
br list
sbframe object is not valid.
```
which is still not perfect, but at least it's not misleading.
But one made in a situation where that's impossible might only have an
error, and no symbol context, so that's not necessarily true. Check for
the target's validity before using it.
Fixes issue #93313
This has been flaky for a while, for example
https://lab.llvm.org/buildbot/#/builders/96/builds/50350
```
Command Output (stdout):
--
lldb version 18.0.0git (https://github.com/llvm/llvm-project.git revision 3974d89bde66a2ec61261b969b51993da81205c7)
clang revision 3974d89bde66a2ec61261b969b51993da81205c7
llvm revision 3974d89bde66a2ec61261b969b51993da81205c7
"can't evaluate expressions when the process is running."
```
```
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
#0 0x0000ffffa46191a0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x529a1a0)
#1 0x0000ffffa4617144 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x5298144)
#2 0x0000ffffa46198d0 SignalHandler(int) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x529a8d0)
#3 0x0000ffffab25b7dc (linux-vdso.so.1+0x7dc)
#4 0x0000ffffab13d050 /build/glibc-Q8DG8B/glibc-2.31/string/../sysdeps/aarch64/multiarch/memcpy_advsimd.S:92:0
#5 0x0000ffffa446f420 lldb_private::process_gdb_remote::GDBRemoteRegisterContext::PrivateSetRegisterValue(unsigned int, llvm::ArrayRef<unsigned char>) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x50f0420)
#6 0x0000ffffa446f7b8 lldb_private::process_gdb_remote::GDBRemoteRegisterContext::GetPrimordialRegister(lldb_private::RegisterInfo const*, lldb_private::process_gdb_remote::GDBRemoteCommunicationClient&) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x50f07b8)
#7 0x0000ffffa446f308 lldb_private::process_gdb_remote::GDBRemoteRegisterContext::ReadRegisterBytes(lldb_private::RegisterInfo const*) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x50f0308)
#8 0x0000ffffa446ec1c lldb_private::process_gdb_remote::GDBRemoteRegisterContext::ReadRegister(lldb_private::RegisterInfo const*, lldb_private::RegisterValue&) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x50efc1c)
#9 0x0000ffffa412eaa4 lldb_private::RegisterContext::ReadRegisterAsUnsigned(lldb_private::RegisterInfo const*, unsigned long) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x4dafaa4)
#10 0x0000ffffa420861c ReadLinuxProcessAddressMask(std::shared_ptr<lldb_private::Process>, llvm::StringRef) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x4e8961c)
#11 0x0000ffffa4208430 ABISysV_arm64::FixCodeAddress(unsigned long) (/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lib/python3.8/site-packages/lldb/_lldb.cpython-38-aarch64-linux-gnu.so+0x4e89430)
```
Judging by the backtrace something is trying to read the pointer authentication address/code mask
registers. This explains why I've not seen this issue locally, as the buildbot runs on Graviton
3 with has the pointer authentication extension.
I will try to reproduce, fix and re-enable the test.
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
initial stop. The code was using PrivateResume when it should have
used Resume.
This was allowing expression evaluation while the target was running,
and though that was caught a litle later on, we should never have gotten
that far. To make sure that this is caught immediately I made an error
SBValue when this happens, and test that we get this error.
Differential Revision: https://reviews.llvm.org/D144665
