[all-commits] [llvm/llvm-project] 38b252: Disable ThreadPlanSingleThreadTimeout during step ...

[jeffreytan81 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 38b252aa45abad53d7c07c666569b174a215d94d
      https://github.com/llvm/llvm-project/commit/38b252aa45abad53d7c07c666569b174a215d94d
  Author: jeffreytan81 <jeffreytan at meta.com>
  Date:   2024-08-28 (Wed, 28 Aug 2024)

  Changed paths:
    M lldb/include/lldb/Target/ThreadPlan.h
    M lldb/include/lldb/Target/ThreadPlanStepOverBreakpoint.h
    M lldb/source/Target/ThreadPlanSingleThreadTimeout.cpp
    M lldb/source/Target/ThreadPlanStepOverBreakpoint.cpp

  Log Message:
  -----------
  Disable ThreadPlanSingleThreadTimeout during step over breakpoint  (#104532)

This PR fixes another race condition in
https://github.com/llvm/llvm-project/pull/90930. The failure was found
by @labath with this log: https://paste.debian.net/hidden/30235a5c/:
```
dotest_wrapper.  <  15> send packet: $z0,224505,1#65
...
b-remote.async>  <  22> send packet: $vCont;s:p1dcf.1dcf#4c
intern-state     GDBRemoteClientBase::Lock::Lock sent packet: \x03
b-remote.async>  < 818> read packet: $T13thread:p1dcf.1dcf;name:a.out;threads:1dcf,1dd2;jstopinfo:5b7b226e616d65223a22612e6f7574222c22726561736f6e223a227369676e616c222c227369676e616c223a31392c22746964223a373633317d2c7b226e616d65223a22612e6f7574222c22746964223a373633347d5d;thread-pcs:0000000000224505,00007f4e4302119a;00:0000000000000000;01:0000000000000000;02:0100000000000000;03:0000000000000000;04:9084997dfc7f0000;05:a8742a0000000000;06:b084997dfc7f0000;07:6084997dfc7f0000;08:0000000000000000;09:00d7e5424e7f0000;0a:d0d9e5424e7f0000;0b:0202000000000000;0c:80cc290000000000;0d:d8cc1c434e7f0000;0e:2886997dfc7f0000;0f:0100000000000000;10:0545220000000000;11:0602000000000000;12:3300000000000000;13:0000000000000000;14:0000000000000000;15:2b00000000000000;16:80fbe5424e7f0000;17:0000000000000000;18:0000000000000000;19:0000000000000000;reason:signal;#b9
```
It shows an async interrupt "\x03" was sent immediately after `vCont;s`
single step over breakpoint at address `0x224505` (which was disabled
before vCont). And the later stop was still at the original PC
(0x224505) not moving forward.

The investigation shows the failure happens when timeout is short and
async interrupt is sent to lldb-server immediately after vCont so
ptrace() resumes and then async interrupts debuggee immediately so
debuggee does not get a chance to execute and move PC. So it enters stop
mode immediately at original PC. `ThreadPlanStepOverBreakpoint` does not
expect PC not moving and reports stop at the original place.

To fix this, the PR prevents `ThreadPlanSingleThreadTimeout` from being
created during `ThreadPlanStepOverBreakpoint` by introduces a new
`SupportsResumeOthers()` method and `ThreadPlanStepOverBreakpoint`
returns false for it. This makes sense because we should never resume
threads during step over breakpoint anyway otherwise it might cause
other threads to miss breakpoint.

---------

Co-authored-by: jeffreytan81 <jeffreytan at fb.com>



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