[lldb] [client] Implement follow-fork-mode

[mgorny]

Summary

Implement a new target.process.follow-fork-mode setting to control
LLDB's behavior on fork. If set to 'parent', the forked child is
detached and parent continues being traced. If set to 'child',
the parent is detached and child becomes traced instead.

[mgorny]

This is it! The fruit of my labor! It feels like it's... kinda small. But I guess this is because all the groundwork has been done well, and now it's just a matter of plugging it in.

[mgorny]

Rebase. Do not run tests on NetBSD yet.

[JDevlieghere]

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

5513–5522

Should we lock the WatchpointList while iterating over it? If so I think that class could benefit from an Iterable (like D105914) that will lock during iteration, which would also simplify this code a bit.

[mgorny]

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

5513–5522

Indeed that sounds like a good idea. Opened D106263 for it. I'll update this one once that one is merged.

[mgorny]

Rebased. Switched to watchpoint iterator API.

[vadimcn]

@mgorny Do your changes allow debugging both the parent and child processes after a fork?

[mgorny]

In D100503#2894584, @vadimcn wrote:

@mgorny Do your changes allow debugging both the parent and child processes after a fork?

No. This patch supports choosing either the parent or the child but it's a step in that direction. Further work is necessary to support debugging multiple processes simultaneously.

[mgorny]

Rebased. Changed hw breakpoint sizes to match the normal sending code.

[krytarowski]

Looks good

[thakis]

The new tests here fall for me on macOS:

[4303/4304] Running lldb shell test suite
llvm-lit: /Users/thakis/src/llvm-project/lldb/test/Shell/helper/toolchain.py:126: note: using SDKROOT: '/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk'
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:436: note: using clang: /Users/thakis/src/llvm-build-project/bin/clang
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:436: note: using ld.lld: /Users/thakis/src/llvm-build-project/bin/ld.lld
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:436: note: using lld-link: /Users/thakis/src/llvm-build-project/bin/lld-link
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:436: note: using ld64.lld: /Users/thakis/src/llvm-build-project/bin/ld64.lld
llvm-lit: /Users/thakis/src/llvm-project/llvm/utils/lit/lit/llvm/config.py:436: note: using wasm-ld: /Users/thakis/src/llvm-build-project/bin/wasm-ld
llvm-lit: /Users/thakis/src/llvm-project/lldb/test/Shell/lit.cfg.py:98: warning: Could not set a default per-test timeout. Requires the Python psutil module but it could not be found. Try installing it via pip or via your operating system's package manager.
FAIL: lldb-shell :: Subprocess/fork-follow-child.test (433 of 437)
******************** TEST 'lldb-shell :: Subprocess/fork-follow-child.test' FAILED ********************
Script:
--
: 'RUN: at line 3';   /Users/thakis/src/llvm-build-project/bin/clang --driver-mode=g++ --target=specify-a-target-or-use-a-_host-substitution --target=x86_64-apple-darwin19.6.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/Inputs/fork.cpp -DTEST_FORK=fork -o /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child.test.tmp
: 'RUN: at line 4';   /Users/thakis/src/llvm-build-project/bin/lldb --no-lldbinit -S /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init -b -s /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child.test /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child.test.tmp | /Users/thakis/src/llvm-build-project/bin/FileCheck /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child.test
--
Exit Code: 1

Command Output (stderr):
--
clang-13: warning: argument unused during compilation: '-fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell' [-Wunused-command-line-argument]
/Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child.test:9:10: error: CHECK: expected string not found in input
# CHECK: child exited: 0
         ^
<stdin>:26:69: note: scanning from here
 0x100003cee <+14>: leaq 0x21b(%rip), %rdi ; "function run in parent\n"
                                                                    ^
<stdin>:27:115: note: possible intended match here
Process 39485 launched: '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child.test.tmp' (x86_64)
                                                                                                                  ^

Input file: <stdin>
Check file: /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           .
           .
           .
          21:  frame #0: 0x0000000100003ce0 fork-follow-child.test.tmp`parent_func()
          22: fork-follow-child.test.tmp`parent_func:
          23: -> 0x100003ce0 <+0>: pushq %rbp
          24:  0x100003ce1 <+1>: movq %rsp, %rbp
          25:  0x100003ce4 <+4>: movl $0x1, 0x434a(%rip) ; _dyld_private + 4
          26:  0x100003cee <+14>: leaq 0x21b(%rip), %rdi ; "function run in parent\n"
check:9'0                                                                         X~~~ error: no match found
          27: Process 39485 launched: '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child.test.tmp' (x86_64)
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:9'1                                                                                                                       ?                         possible intended match
>>>>>>

--

********************
FAIL: lldb-shell :: Subprocess/vfork-follow-child.test (434 of 437)
******************** TEST 'lldb-shell :: Subprocess/vfork-follow-child.test' FAILED ********************
Script:
--
: 'RUN: at line 3';   /Users/thakis/src/llvm-build-project/bin/clang --driver-mode=g++ --target=specify-a-target-or-use-a-_host-substitution --target=x86_64-apple-darwin19.6.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/Inputs/fork.cpp -DTEST_FORK=vfork -o /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child.test.tmp
: 'RUN: at line 4';   /Users/thakis/src/llvm-build-project/bin/lldb --no-lldbinit -S /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init -b -s /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child.test /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child.test.tmp | /Users/thakis/src/llvm-build-project/bin/FileCheck /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child.test
--
Exit Code: 1

Command Output (stderr):
--
clang-13: warning: argument unused during compilation: '-fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell' [-Wunused-command-line-argument]
/Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child.test:9:10: error: CHECK: expected string not found in input
# CHECK: child exited: 0
         ^
<stdin>:26:69: note: scanning from here
 0x100003cee <+14>: leaq 0x21b(%rip), %rdi ; "function run in parent\n"
                                                                    ^
<stdin>:27:116: note: possible intended match here
Process 39484 launched: '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child.test.tmp' (x86_64)
                                                                                                                   ^

Input file: <stdin>
Check file: /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           .
           .
           .
          21:  frame #0: 0x0000000100003ce0 vfork-follow-child.test.tmp`parent_func()
          22: vfork-follow-child.test.tmp`parent_func:
          23: -> 0x100003ce0 <+0>: pushq %rbp
          24:  0x100003ce1 <+1>: movq %rsp, %rbp
          25:  0x100003ce4 <+4>: movl $0x1, 0x434a(%rip) ; _dyld_private + 4
          26:  0x100003cee <+14>: leaq 0x21b(%rip), %rdi ; "function run in parent\n"
check:9'0                                                                         X~~~ error: no match found
          27: Process 39484 launched: '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child.test.tmp' (x86_64)
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:9'1                                                                                                                        ?                         possible intended match
>>>>>>

--

********************
FAIL: lldb-shell :: Subprocess/fork-follow-child-softbp.test (435 of 437)
******************** TEST 'lldb-shell :: Subprocess/fork-follow-child-softbp.test' FAILED ********************
Script:
--
: 'RUN: at line 3';   /Users/thakis/src/llvm-build-project/bin/clang --driver-mode=g++ --target=specify-a-target-or-use-a-_host-substitution --target=x86_64-apple-darwin19.6.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/Inputs/fork.cpp -DTEST_FORK=fork -o /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child-softbp.test.tmp
: 'RUN: at line 4';   /Users/thakis/src/llvm-build-project/bin/lldb --no-lldbinit -S /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init -b -s /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-softbp.test /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child-softbp.test.tmp | /Users/thakis/src/llvm-build-project/bin/FileCheck /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-softbp.test
--
Exit Code: 1

Command Output (stderr):
--
clang-13: warning: argument unused during compilation: '-fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell' [-Wunused-command-line-argument]
/Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-softbp.test:10:15: error: CHECK-NEXT: expected string not found in input
# CHECK-NEXT: child_func
              ^
<stdin>:22:71: note: scanning from here
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
                                                                      ^
<stdin>:23:43: note: possible intended match here
 frame #0: 0x0000000100003ce0 fork-follow-child-softbp.test.tmp`parent_func()
                                          ^

Input file: <stdin>
Check file: /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-softbp.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           .
           .
           .
          17: Breakpoint 1: where = fork-follow-child-softbp.test.tmp`child_func(void*), address = 0x0000000100003d00
          18: (lldb) b parent_func
          19: Breakpoint 2: where = fork-follow-child-softbp.test.tmp`parent_func(), address = 0x0000000100003ce0
          20: (lldb) process launch
          21: Process 39486 stopped
          22: * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
next:10'0                                                                           X~~~~ error: no match found
          23:  frame #0: 0x0000000100003ce0 fork-follow-child-softbp.test.tmp`parent_func()
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
next:10'1                                               ?                                    possible intended match
          24: fork-follow-child-softbp.test.tmp`parent_func:
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          25: -> 0x100003ce0 <+0>: pushq %rbp
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          26:  0x100003ce1 <+1>: movq %rsp, %rbp
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          27:  0x100003ce4 <+4>: movl $0x1, 0x434a(%rip) ; _dyld_private + 4
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          28:  0x100003cee <+14>: leaq 0x21b(%rip), %rdi ; "function run in parent\n"
next:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           .
           .
           .
>>>>>>

--

********************
FAIL: lldb-shell :: Subprocess/fork-follow-child-wp.test (436 of 437)
******************** TEST 'lldb-shell :: Subprocess/fork-follow-child-wp.test' FAILED ********************
Script:
--
: 'RUN: at line 3';   /Users/thakis/src/llvm-build-project/bin/clang --driver-mode=g++ --target=specify-a-target-or-use-a-_host-substitution --target=x86_64-apple-darwin19.6.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell -g /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/Inputs/fork.cpp -DTEST_FORK=fork -o /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child-wp.test.tmp
: 'RUN: at line 4';   /Users/thakis/src/llvm-build-project/bin/lldb --no-lldbinit -S /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init -b -s /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-wp.test /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/fork-follow-child-wp.test.tmp | /Users/thakis/src/llvm-build-project/bin/FileCheck /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-wp.test
--
Exit Code: 1

Command Output (stderr):
--
clang-13: warning: argument unused during compilation: '-fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell' [-Wunused-command-line-argument]
error: Process must be launched.
/Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-wp.test:12:10: error: CHECK: expected string not found in input
# CHECK: stop reason = watchpoint
         ^
<stdin>:29:71: note: scanning from here
* thread #1, queue = 'com.apple.main-thread', stop reason = watchpoint 1
                                                                      ^
<stdin>:40:4: note: possible intended match here
function run in parent
   ^

Input file: <stdin>
Check file: /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/fork-follow-child-wp.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            .
            .
            .
           24: Watchpoint 1 hit:
           25: old value: 0
           26: new value: 1
           27: Process 39492 resuming
           28: Process 39492 stopped
           29: * thread #1, queue = 'com.apple.main-thread', stop reason = watchpoint 1
check:12'0                                                                           X~~ error: no match found
           30:  frame #0: 0x0000000100003cee fork-follow-child-wp.test.tmp`parent_func() at fork.cpp:15:3
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           31:  12
check:12'0     ~~~~~
           32:  13 void parent_func() {
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~
           33:  14 g_val = 1;
check:12'0     ~~~~~~~~~~~~~~~
           34: -> 15 printf("function run in parent\n");
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           35:  ^
check:12'0     ~~~
           36:  16 }
check:12'0     ~~~~~~
           37:  17
check:12'0     ~~~~~
           38:  18 int child_func(void *unused) {
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           39: (lldb) continue
check:12'0     ~~~~~~~~~~~~~~~~
           40: function run in parent
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~
check:12'1        ?                    possible intended match
           41: child exited: 0
check:12'0     ~~~~~~~~~~~~~~~~
           42: Process 39492 resuming
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~
           43: Process 39492 exited with status = 0 (0x00000000)
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           44: (lldb) continue
check:12'0     ~~~~~~~~~~~~~~~~
>>>>>>

--

********************
FAIL: lldb-shell :: Subprocess/vfork-follow-child-softbp.test (437 of 437)
******************** TEST 'lldb-shell :: Subprocess/vfork-follow-child-softbp.test' FAILED ********************
Script:
--
: 'RUN: at line 3';   /Users/thakis/src/llvm-build-project/bin/clang --driver-mode=g++ --target=specify-a-target-or-use-a-_host-substitution --target=x86_64-apple-darwin19.6.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/Inputs/fork.cpp -DTEST_FORK=vfork -o /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child-softbp.test.tmp
: 'RUN: at line 4';   /Users/thakis/src/llvm-build-project/bin/lldb --no-lldbinit -S /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init -b -s /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child-softbp.test /Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child-softbp.test.tmp | /Users/thakis/src/llvm-build-project/bin/FileCheck /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child-softbp.test
--
Exit Code: 1

Command Output (stderr):
--
clang-13: warning: argument unused during compilation: '-fmodules-cache-path=/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-clang/lldb-shell' [-Wunused-command-line-argument]
/Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child-softbp.test:9:10: error: CHECK: expected string not found in input
# CHECK: function run in parent
         ^
<stdin>:1:1: note: scanning from here
(lldb) command source -s 0 '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init'
^
<stdin>:6:8: note: possible intended match here
(lldb) settings set interpreter.echo-comment-commands false
       ^

Input file: <stdin>
Check file: /Users/thakis/src/llvm-project/lldb/test/Shell/Subprocess/vfork-follow-child-softbp.test

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           1: (lldb) command source -s 0 '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init'
check:9'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           2: Executing commands in '/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/lit-lldb-init'.
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           3: (lldb) # LLDB init file for the LIT tests.
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           4: (lldb) settings set symbols.enable-external-lookup false
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           5: (lldb) settings set plugin.process.gdb-remote.packet-timeout 60
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           6: (lldb) settings set interpreter.echo-comment-commands false
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:9'1            ?                                                     possible intended match
           7: (lldb) settings set symbols.clang-modules-cache-path "/Users/thakis/src/llvm-build-project/lldb-test-build.noindex/module-cache-lldb"
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           8: (lldb) settings set target.auto-apply-fixits false
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           9: (lldb) settings set target.inherit-tcc true
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          10: (lldb) settings set target.detach-on-error false
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          11: (lldb) target create "/Users/thakis/src/llvm-build-project/tools/lldb/test/Shell/Subprocess/Output/vfork-follow-child-softbp.test.tmp"
check:9'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           .
           .
           .
>>>>>>

--

********************
********************
Failed Tests (5):
  lldb-shell :: Subprocess/fork-follow-child-softbp.test
  lldb-shell :: Subprocess/fork-follow-child-wp.test
  lldb-shell :: Subprocess/fork-follow-child.test
  lldb-shell :: Subprocess/vfork-follow-child-softbp.test
  lldb-shell :: Subprocess/vfork-follow-child.test

[mgorny]

I'm sorry about looking into it this late. I've just marked them all unsupported on Darwin.

lldb/include/lldb/Target/Process.h

public:
   bool GetWarningsOptimization() const;
   bool GetWarningsUnsupportedLanguage() const;
   bool GetStopOnExec() const;
   std::chrono::seconds GetUtilityExpressionTimeout() const;
   std::chrono::seconds GetInterruptTimeout() const;
   bool GetOSPluginReportsAllThreads() const;
   void SetOSPluginReportsAllThreads(bool does_report);
   bool GetSteppingRunsAllThreads() const;
+  FollowForkMode GetFollowForkMode() const;
 
 protected:
   Process *m_process; // Can be nullptr for global ProcessProperties
   std::unique_ptr<ProcessExperimentalProperties> m_experimental_properties_up;
 };
 
 typedef std::shared_ptr<ProcessProperties> ProcessPropertiesSP;
 

lldb/include/lldb/lldb-private-enumerations.h

 
 // Loading modules from memory
 enum MemoryModuleLoadLevel {
   eMemoryModuleLoadLevelMinimal,  // Load sections only
   eMemoryModuleLoadLevelPartial,  // Load function bounds but no symbols
   eMemoryModuleLoadLevelComplete, // Load sections and all symbols
 };
 
+// Behavior on fork/vfork
+enum FollowForkMode {
+  eFollowParent, // Follow parent process
+  eFollowChild,  // Follow child process
+};
+
 // Result enums for when reading multiple lines from IOHandlers
 enum class LineStatus {
   Success, // The line that was just edited if good and should be added to the
            // lines
   Status,  // There is an error with the current line and it needs to be
            // re-edited
            // before it can be accepted
   Done     // Lines are complete

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h

public:
   StructuredData::ObjectSP GetSharedCacheInfo() override;
 
   std::string HarmonizeThreadIdsForProfileData(
       StringExtractorGDBRemote &inputStringExtractor);
 
   void DidFork(lldb::pid_t child_pid, lldb::tid_t child_tid) override;
   void DidVFork(lldb::pid_t child_pid, lldb::tid_t child_tid) override;
   void DidVForkDone() override;
+  void DidExec() override;
 
 protected:
   friend class ThreadGDBRemote;
   friend class GDBRemoteCommunicationClient;
   friend class GDBRemoteRegisterContext;
 
   bool SupportsMemoryTagging() override;
 
private:
   llvm::DenseMap<ModuleCacheKey, ModuleSpec, ModuleCacheInfo>
       m_cached_module_specs;
 
   ProcessGDBRemote(const ProcessGDBRemote &) = delete;
   const ProcessGDBRemote &operator=(const ProcessGDBRemote &) = delete;
 
   // fork helpers
   void DidForkSwitchSoftwareBreakpoints(bool enable);
+  void DidForkSwitchHardwareTraps(bool enable);
 };
 
 } // namespace process_gdb_remote
 } // namespace lldb_private
 
 #endif // LLDB_SOURCE_PLUGINS_PROCESS_GDB_REMOTE_PROCESSGDBREMOTE_H

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

if (bp_site->IsEnabled() &&
          bp_site->GetType() == BreakpointSite::eExternal)) {
       m_gdb_comm.SendGDBStoppointTypePacket(
           eBreakpointSoftware, enable, bp_site->GetLoadAddress(),
           GetSoftwareBreakpointTrapOpcode(bp_site), GetInterruptTimeout());
     }
   });
 }
 
+void ProcessGDBRemote::DidForkSwitchHardwareTraps(bool enable) {
+  if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointHardware)) {
+    GetBreakpointSiteList().ForEach([this, enable](BreakpointSite *bp_site) {
+      if (bp_site->IsEnabled() &&
+          bp_site->GetType() == BreakpointSite::eHardware) {
+        m_gdb_comm.SendGDBStoppointTypePacket(
+            eBreakpointHardware, enable, bp_site->GetLoadAddress(),
+            GetSoftwareBreakpointTrapOpcode(bp_site), GetInterruptTimeout());
+      }
+    });
+  }
+
+  WatchpointList &wps = GetTarget().GetWatchpointList();
+  size_t wp_count = wps.GetSize();
+  for (size_t i = 0; i < wp_count; ++i) {
+    WatchpointSP wp = wps.GetByIndex(i);
+    if (wp->IsEnabled()) {
+      GDBStoppointType type = GetGDBStoppointType(wp.get());
+      m_gdb_comm.SendGDBStoppointTypePacket(type, enable, wp->GetLoadAddress(),
+                                            wp->GetByteSize(),
+                                            GetInterruptTimeout());
+    }
+  }
+}
+
 void ProcessGDBRemote::DidFork(lldb::pid_t child_pid, lldb::tid_t child_tid) {
   Log *log(ProcessGDBRemoteLog::GetLogIfAllCategoriesSet(GDBR_LOG_PROCESS));
 
   lldb::pid_t parent_pid = m_gdb_comm.GetCurrentProcessID();
   // Any valid TID will suffice, thread-relevant actions will set a proper TID
   // anyway.
   lldb::tid_t parent_tid = m_thread_ids.front();
 
-  if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware)) {
-    // Switch to the new process to clear breakpoints there.
-    if (!m_gdb_comm.SetCurrentThread(child_tid, child_pid)) {
-      LLDB_LOG(log, "ProcessGDBRemote::DidFork() unable to set pid/tid");
-      return;
-    }
+  lldb::pid_t follow_pid, detach_pid;
+  lldb::tid_t follow_tid, detach_tid;
+
+  switch (GetFollowForkMode()) {
+  case eFollowParent:
+    follow_pid = parent_pid;
+    follow_tid = parent_tid;
+    detach_pid = child_pid;
+    detach_tid = child_tid;
+    break;
+  case eFollowChild:
+    follow_pid = child_pid;
+    follow_tid = child_tid;
+    detach_pid = parent_pid;
+    detach_tid = parent_tid;
+    break;
+  }
+
+  // Switch to the process that is going to be detached.
+  if (!m_gdb_comm.SetCurrentThread(detach_tid, detach_pid)) {
 
-    // Disable all software breakpoints in the forked process.
+  if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware))
     DidForkSwitchSoftwareBreakpoints(false);
 
-    // Reset gdb-remote to the original process.
-    if (!m_gdb_comm.SetCurrentThread(parent_tid, parent_pid)) {
-      LLDB_LOG(log, "ProcessGDBRemote::DidFork() unable to reset pid/tid");
-      return;
-    }
-  }
+  // Remove hardware breakpoints / watchpoints from parent process if we're
+  // following child.
+  if (GetFollowForkMode() == eFollowChild)
+    DidForkSwitchHardwareTraps(false);
+
+  // Switch to the process that is going to be followed
+  if (!m_gdb_comm.SetCurrentThread(follow_tid, follow_pid) ||
+      !m_gdb_comm.SetCurrentThreadForRun(follow_tid, follow_pid)) {
 
-  LLDB_LOG(log, "Detaching forked child {0}", child_pid);
-  Status error = m_gdb_comm.Detach(false, child_pid);
+  LLDB_LOG(log, "Detaching process {0}", detach_pid);
+  Status error = m_gdb_comm.Detach(false, detach_pid);
   if (error.Fail()) {
     LLDB_LOG(log, "ProcessGDBRemote::DidFork() detach packet send failed: {0}",
              error.AsCString() ? error.AsCString() : "<unknown error>");
     return;
   }
+
+  // Hardware breakpoints/watchpoints are not inherited implicitly,
+  // so we need to readd them if we're following child.
+  if (GetFollowForkMode() == eFollowChild)
+    DidForkSwitchHardwareTraps(true);
 }
 
 void ProcessGDBRemote::DidVFork(lldb::pid_t child_pid, lldb::tid_t child_tid) {
   Log *log(ProcessGDBRemoteLog::GetLogIfAllCategoriesSet(GDBR_LOG_PROCESS));
 
   assert(!m_vfork_in_progress);
   m_vfork_in_progress = true;
 
   // Disable all software breakpoints for the duration of vfork.
   if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware))
     DidForkSwitchSoftwareBreakpoints(false);
 
-  LLDB_LOG(log, "Detaching forked child {0}", child_pid);
-  Status error = m_gdb_comm.Detach(false, child_pid);
+  lldb::pid_t detach_pid;
+  lldb::tid_t detach_tid;
+
+  switch (GetFollowForkMode()) {
+  case eFollowParent:
+    detach_pid = child_pid;
+    detach_tid = child_tid;
+    break;
+  case eFollowChild:
+    detach_pid = m_gdb_comm.GetCurrentProcessID();
+    // Any valid TID will suffice, thread-relevant actions will set a proper TID
+    // anyway.
+    detach_tid = m_thread_ids.front();
+
+    // Switch to the parent process before detaching it.
+    if (!m_gdb_comm.SetCurrentThread(detach_tid, detach_pid)) {
+      LLDB_LOG(log, "ProcessGDBRemote::DidFork() unable to set pid/tid");
+      return;
+    }
+
+    // Remove hardware breakpoints / watchpoints from the parent process.
+    DidForkSwitchHardwareTraps(false);
+
+    // Switch to the child process.
+    if (!m_gdb_comm.SetCurrentThread(child_tid, child_pid) ||
+        !m_gdb_comm.SetCurrentThreadForRun(child_tid, child_pid)) {
+      LLDB_LOG(log, "ProcessGDBRemote::DidFork() unable to reset pid/tid");
+      return;
+    }
+    break;
+  }
+
+  LLDB_LOG(log, "Detaching process {0}", detach_pid);
+  Status error = m_gdb_comm.Detach(false, detach_pid);
   if (error.Fail()) {
       LLDB_LOG(log,
                "ProcessGDBRemote::DidFork() detach packet send failed: {0}",
                 error.AsCString() ? error.AsCString() : "<unknown error>");
       return;
   }
 }
 
 void ProcessGDBRemote::DidVForkDone() {
   assert(m_vfork_in_progress);
   m_vfork_in_progress = false;
 
   // Reenable all software breakpoints that were enabled before vfork.
   if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware))
     DidForkSwitchSoftwareBreakpoints(true);
 }
+
+void ProcessGDBRemote::DidExec() {
+  // If we are following children, vfork is finished by exec (rather than
+  // vforkdone that is submitted for parent).
+  if (GetFollowForkMode() == eFollowChild)
+    m_vfork_in_progress = false;
+  Process::DidExec();
+}

lldb/source/Target/Process.cpp

if (exe_ctx) {
         if (this != instance_properties)
           return instance_properties->ProtectedGetPropertyAtIndex(idx);
       }
     }
     return ProtectedGetPropertyAtIndex(idx);
   }
 };
 
+static constexpr OptionEnumValueElement g_follow_fork_mode_values[] = {
+    {
+        eFollowParent,
+        "parent",
+        "Continue tracing the parent process and detach the child.",
+    },
+    {
+        eFollowChild,
+        "child",
+        "Trace the child process and detach the parent.",
+    },
+};
+
 #define LLDB_PROPERTIES_process
 #include "TargetProperties.inc"
 
 enum {
 #define LLDB_PROPERTIES_process
 #include "TargetPropertiesEnum.inc"
   ePropertyExperimental,
 };
const Property *exp_property =
       m_collection_sp->GetPropertyAtIndex(nullptr, true, ePropertyExperimental);
   OptionValueProperties *exp_values =
       exp_property->GetValue()->GetAsProperties();
   if (exp_values)
     exp_values->SetPropertyAtIndexAsBoolean(
         nullptr, ePropertyOSPluginReportsAllThreads, does_report);
 }
 
+FollowForkMode ProcessProperties::GetFollowForkMode() const {
+  const uint32_t idx = ePropertyFollowForkMode;
+  return (FollowForkMode)m_collection_sp->GetPropertyAtIndexAsEnumeration(
+      nullptr, idx, g_process_properties[idx].default_uint_value);
+}
+
 ProcessSP Process::FindPlugin(lldb::TargetSP target_sp,
                               llvm::StringRef plugin_name,
                               ListenerSP listener_sp,
                               const FileSpec *crash_file_path,
                               bool can_connect) {
   static uint32_t g_process_unique_id = 0;
 
   ProcessSP process_sp;

lldb/source/Target/TargetProperties.td

def InterruptTimeout: Property<"interrupt-timeout", "UInt64">,
     DefaultUnsignedValue<20>,
     Desc<"The time in seconds to wait for an interrupt succeed in stopping the target.">;
   def SteppingRunsAllThreads: Property<"run-all-threads", "Boolean">,
     DefaultFalse,
     Desc<"If true, stepping operations will run all threads.  This is equivalent to setting the run-mode option to 'all-threads'.">;
   def VirtualAddressableBits: Property<"virtual-addressable-bits", "UInt64">,
     DefaultUnsignedValue<0>,
     Desc<"The number of bits used for addressing. If the value is 39, then bits 0..38 are used for addressing. The default value of 0 means unspecified.">;
+  def FollowForkMode: Property<"follow-fork-mode", "Enum">,
+    DefaultEnumValue<"eFollowParent">,
+    EnumValues<"OptionEnumValues(g_follow_fork_mode_values)">,
+    Desc<"Debugger's behavior upon fork or vfork.">;
 }
 
 let Definition = "platform" in {
   def UseModuleCache: Property<"use-module-cache", "Boolean">,
     Global,
     DefaultTrue,
     Desc<"Use module cache.">;
   def ModuleCacheDirectory: Property<"module-cache-directory", "FileSpec">,

lldb/test/Shell/Subprocess/clone-follow-child-softbp.test

+# REQUIRES: native && system-linux
+# clone() tests fails on arm64 Linux, PR #49899
+# UNSUPPORTED: system-linux && target-aarch64
+# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_CLONE -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+b child_func
+b parent_func
+process launch
+# CHECK: stop reason = breakpoint
+# CHECK-NEXT: child_func
+continue
+# CHECK: child exited: 0

lldb/test/Shell/Subprocess/clone-follow-child-wp.test

+# REQUIRES: native && system-linux && dbregs-set
+# clone() tests fails on arm64 Linux, PR #49899
+# UNSUPPORTED: system-linux && target-aarch64
+# RUN: %clangxx_host -g %p/Inputs/fork.cpp -DTEST_CLONE -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+process launch -s
+watchpoint set variable -w write g_val
+# CHECK: Watchpoint created:
+continue
+# CHECK: stop reason = watchpoint
+continue
+# CHECK: stop reason = watchpoint
+continue
+# CHECK: child exited: 0

lldb/test/Shell/Subprocess/clone-follow-child.test

+# REQUIRES: native && system-linux
+# clone() tests fails on arm64 Linux, PR #49899
+# UNSUPPORTED: system-linux && target-aarch64
+# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_CLONE -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+b parent_func
+process launch
+# CHECK: function run in parent
+# CHECK: child exited: 0

lldb/test/Shell/Subprocess/fork-follow-child-softbp.test

 # REQUIRES: native
-# UNSUPPORTED: system-darwin
 # UNSUPPORTED: system-windows
 # RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=fork -o %t
 # RUN: %lldb -b -s %s %t | FileCheck %s
-b parent_func
+settings set target.process.follow-fork-mode child
 b child_func
+b parent_func
 process launch
-# CHECK-NOT: function run in parent
 # CHECK: stop reason = breakpoint
+# CHECK-NEXT: child_func
 continue
-# CHECK: function run in parent
 # CHECK: child exited: 0

lldb/test/Shell/Subprocess/fork-follow-child-wp.test

+# REQUIRES: native && dbregs-set
+# UNSUPPORTED: system-windows
+# RUN: %clangxx_host -g %p/Inputs/fork.cpp -DTEST_FORK=fork -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+process launch -s
+watchpoint set variable -w write g_val
+# CHECK: Watchpoint created:
+continue
+# CHECK: stop reason = watchpoint
+continue
+# CHECK: stop reason = watchpoint
+continue
+# CHECK: child exited: 0

lldb/test/Shell/Subprocess/fork-follow-child.test

 # REQUIRES: native
-# UNSUPPORTED: system-darwin
 # UNSUPPORTED: system-windows
 # RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=fork -o %t
 # RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
 b parent_func
-b child_func
 process launch
-# CHECK-NOT: function run in parent
-# CHECK: stop reason = breakpoint
-continue
 # CHECK: function run in parent
 # CHECK: child exited: 0

lldb/test/Shell/Subprocess/fork-follow-parent-softbp.test

 # REQUIRES: native
 # UNSUPPORTED: system-darwin
 # UNSUPPORTED: system-windows
 # RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=fork -o %t
 # RUN: %lldb -b -s %s %t | FileCheck %s
 b parent_func
 b child_func
 process launch
 # CHECK-NOT: function run in parent
 # CHECK: stop reason = breakpoint
+# CHECK-NEXT: parent_func
 continue
 # CHECK: function run in parent
 # CHECK: child exited: 0

lldb/test/Shell/Subprocess/vfork-follow-child-softbp.test

 # REQUIRES: native
-# UNSUPPORTED: system-darwin
 # UNSUPPORTED: system-windows
-# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=fork -o %t
+# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=vfork -o %t
 # RUN: %lldb -b -s %s %t | FileCheck %s
-b parent_func
+settings set target.process.follow-fork-mode child
 b child_func
+b parent_func
 process launch
-# CHECK-NOT: function run in parent
-# CHECK: stop reason = breakpoint
-continue
 # CHECK: function run in parent
 # CHECK: child exited: 0

lldb/test/Shell/Subprocess/vfork-follow-child-wp.test

+# REQUIRES: native && dbregs-set
+# UNSUPPORTED: system-windows
+# UNSUPPORTED: system-darwin
+# RUN: %clangxx_host -g %p/Inputs/fork.cpp -DTEST_FORK=vfork -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+process launch -s
+watchpoint set variable -w write g_val
+# CHECK: Watchpoint created:
+continue
+# CHECK: child exited: 0

lldb/test/Shell/Subprocess/vfork-follow-child.test

+# REQUIRES: native
+# UNSUPPORTED: system-windows
+# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=vfork -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+settings set target.process.follow-fork-mode child
+b parent_func
+process launch
+# CHECK: function run in parent
+# CHECK: child exited: 0