[lldb-dap] Incorrect scopes processing in case of multiple frames

[DrSergei]

I found problem with DataBreakpointInfo request when user change selected frame a lot. VSCode doesn’t send repeated Scopes requests for a frame, so the frame from the last Scopes request is selected even after changing frames in the UI. This causes problems with DataBreakpointInfo requests because lldb-dap cannot find variables in this frame. I think the solution is to add frameId to scope's variables reference, allowing scopes from different frames to be distinguished.

[DrSergei]

lldb-dap log

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1751656819.865692139 (stdio) --> {"command":"launch","arguments":{"type":"lldb-dap","request":"launch","name":"Launch (lldb-dap)","program":"/home/sergei/test/main.exe","args":[],"cwd":"/home/sergei/test","__configurationTarget":6,"__sessionId":"1d322a1d-6257-4ab3-bfd8-eb4e94686993"},"type":"request","seq":2}
1751656819.956820011 (stdio) <-- {"command":"launch","request_seq":2,"seq":0,"success":true,"type":"response"}
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1751656819.956998587 (stdio) <-- {"event":"initialized","seq":0,"type":"event"}
1751656819.957040787 (stdio) <-- {"body":{"module":{"addressRange":"0x7ffff7fc3000","id":"276A2448-B2D5-2819-E052-4FB46CFC1168-4A23D111","name":"[vdso]","path":"[vdso]","symbolStatus":"Symbols not found."},"reason":"new"},"event":"module","seq":0,"type":"event"}
1751656819.957118034 (stdio) <-- {"body":{"module":{"addressRange":"0x555555554000","debugInfoSize":"725B","id":"EF51F15C-BFD8-FC78-7717-9F6D4A0D777B-EBB08E8A","name":"main.exe","path":"/home/sergei/test/main.exe","symbolFilePath":"/home/sergei/test/main.exe","symbolStatus":"Symbols loaded."},"reason":"new"},"event":"module","seq":0,"type":"event"}
1751656819.980591536 (stdio) --> {"command":"setBreakpoints","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"lines":[3],"breakpoints":[{"line":3}],"sourceModified":false},"type":"request","seq":3}
1751656819.980821848 (stdio) --> {"command":"setFunctionBreakpoints","arguments":{"breakpoints":[]},"type":"request","seq":4}
1751656819.980875015 (stdio) --> {"command":"setInstructionBreakpoints","arguments":{"breakpoints":[]},"type":"request","seq":5}
1751656819.980926752 (stdio) --> {"command":"setExceptionBreakpoints","arguments":{"filters":[],"filterOptions":[]},"type":"request","seq":6}
1751656819.980949879 (stdio) --> {"command":"setDataBreakpoints","arguments":{"breakpoints":[]},"type":"request","seq":7}
1751656819.989525795 (stdio) <-- {"body":{"breakpoints":[{"column":12,"id":1,"instructionReference":"0x555555555138","line":3,"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"verified":true}]},"command":"setBreakpoints","request_seq":3,"seq":0,"success":true,"type":"response"}
1751656819.989787340 (stdio) <-- {"body":{"breakpoints":[]},"command":"setFunctionBreakpoints","request_seq":4,"seq":0,"success":true,"type":"response"}
1751656819.989926100 (stdio) <-- {"body":{"breakpoints":[]},"command":"setInstructionBreakpoints","request_seq":5,"seq":0,"success":true,"type":"response"}
1751656819.990063429 (stdio) <-- {"body":{},"command":"setExceptionBreakpoints","request_seq":6,"seq":0,"success":true,"type":"response"}
1751656819.990155935 (stdio) <-- {"body":{"breakpoint":{"column":12,"id":1,"instructionReference":"0x555555555138","line":3,"verified":true},"reason":"changed"},"event":"breakpoint","seq":0,"type":"event"}
1751656819.990191460 (stdio) <-- {"body":{"breakpoints":[]},"command":"setDataBreakpoints","request_seq":7,"seq":0,"success":true,"type":"response"}
1751656820.045519352 (stdio) --> {"command":"breakpointLocations","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"line":3},"type":"request","seq":8}
1751656820.045915842 (stdio) <-- {"body":{"breakpoints":[{"column":12,"line":3}]},"command":"breakpointLocations","request_seq":8,"seq":0,"success":true,"type":"response"}
1751656820.076243401 (stdio) --> {"command":"breakpointLocations","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"line":3},"type":"request","seq":9}
1751656820.076744080 (stdio) <-- {"body":{"breakpoints":[{"column":12,"line":3}]},"command":"breakpointLocations","request_seq":9,"seq":0,"success":true,"type":"response"}
1751656820.095665932 (stdio) --> {"command":"configurationDone","type":"request","seq":10}
1751656820.096032619 (stdio) <-- {"body":{"capabilities":{"supportsRestartRequest":true,"supportsStepInTargetsRequest":true}},"event":"capabilities","seq":0,"type":"event"}
1751656820.096253872 (stdio) <-- {"body":{"isLocalProcess":true,"name":"/home/sergei/test/main.exe","startMethod":"launch","systemProcessId":32442},"event":"process","seq":0,"type":"event"}
1751656820.096753836 (stdio) <-- {"command":"configurationDone","request_seq":10,"seq":0,"success":true,"type":"response"}
1751656820.119818926 (stdio) --> {"command":"breakpointLocations","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"line":3},"type":"request","seq":11}
1751656820.120085001 (stdio) --> {"command":"threads","type":"request","seq":12}
1751656820.121870041 (stdio) <-- {"body":{"breakpoints":[{"column":12,"line":3}]},"command":"breakpointLocations","request_seq":11,"seq":0,"success":true,"type":"response"}
1751656820.122054338 (stdio) <-- {"body":{"threads":[{"id":32442,"name":"main.exe"}]},"command":"threads","request_seq":12,"seq":0,"success":true,"type":"response"}
1751656820.363988876 (stdio) <-- {"body":{"module":{"addressRange":"0x7ffff7d9b000","debugInfoSize":"3.5MB","id":"42C84C92-E6F9-8126-B3E2-230EBFDEAD22-C235B667","name":"libc.so.6","path":"/lib/x86_64-linux-gnu/libc.so.6","symbolFilePath":"/usr/lib/debug/.build-id/42/c84c92e6f98126b3e2230ebfdead22c235b667.debug","symbolStatus":"Symbols loaded."},"reason":"new"},"event":"module","seq":0,"type":"event"}
1751656820.368147850 (stdio) <-- {"body":{"allThreadsStopped":true,"description":"breakpoint 1.1","hitBreakpointIds":[1],"preserveFocusHint":false,"reason":"breakpoint","threadCausedFocus":true,"threadId":32442},"event":"stopped","seq":0,"type":"event"}
1751656820.373748064 (stdio) --> {"command":"threads","type":"request","seq":13}
1751656820.374249220 (stdio) <-- {"body":{"threads":[{"id":32442,"name":"main.exe"}]},"command":"threads","request_seq":13,"seq":0,"success":true,"type":"response"}
1751656820.383546829 (stdio) --> {"command":"stackTrace","arguments":{"threadId":32442,"startFrame":0,"levels":1},"type":"request","seq":14}
1751656820.384087086 (stdio) <-- {"body":{"stackFrames":[{"column":12,"id":524288,"instructionPointerReference":"0x555555555138","line":3,"name":"f1()","source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"}}],"totalFrames":21},"command":"stackTrace","request_seq":14,"seq":0,"success":true,"type":"response"}
1751656820.425847530 (stdio) --> {"command":"breakpointLocations","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"line":3},"type":"request","seq":15}
1751656820.426809549 (stdio) <-- {"body":{"breakpoints":[{"column":12,"line":3}]},"command":"breakpointLocations","request_seq":15,"seq":0,"success":true,"type":"response"}
1751656820.799609423 (stdio) --> {"command":"scopes","arguments":{"frameId":524288},"type":"request","seq":16}
1751656820.800187826 (stdio) <-- {"body":{"scopes":[{"expensive":false,"name":"Locals","namedVariables":1,"presentationHint":"locals","variablesReference":1},{"expensive":false,"name":"Globals","namedVariables":0,"variablesReference":2},{"expensive":false,"name":"Registers","namedVariables":3,"presentationHint":"registers","variablesReference":3}]},"command":"scopes","request_seq":16,"seq":0,"success":true,"type":"response"}
1751656820.812552214 (stdio) --> {"command":"variables","arguments":{"variablesReference":1},"type":"request","seq":17}
1751656820.812761784 (stdio) --> {"command":"stackTrace","arguments":{"threadId":32442,"startFrame":1,"levels":19},"type":"request","seq":18}
1751656820.858426094 (stdio) <-- {"body":{"variables":[{"$__lldb_extensions":{"declaration":{"column":9,"line":2,"path":"/home/sergei/test/main.cpp"},"value":"1"},"declarationLocationReference":8,"evaluateName":"a","id":4,"memoryReference":"0x7FFFFFFFDA6C","name":"a","type":"int","value":"1","variablesReference":0}]},"command":"variables","request_seq":17,"seq":0,"success":true,"type":"response"}
1751656820.867719889 (stdio) <-- {"body":{"stackFrames":[{"column":7,"id":524289,"instructionPointerReference":"0x555555555155","line":8,"name":"f2()","source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"}},{"column":7,"id":524290,"instructionPointerReference":"0x555555555172","line":14,"name":"f3()","source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"}},{"column":7,"id":524291,"instructionPointerReference":"0x555555555184","line":19,"name":"main","source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"}},{"column":16,"id":524292,"instructionPointerReference":"0x7FFFF7DC51CA","line":58,"name":"__libc_start_call_main","source":{"name":"libc_start_call_main.h","path":"sysdeps/nptl/libc_start_call_main.h"}},{"column":3,"id":524293,"instructionPointerReference":"0x7FFFF7DC528B","line":360,"name":"__libc_start_main_impl","source":{"name":"libc-start.c","path":"csu/libc-start.c"}},{"column":1,"id":524294,"instructionPointerReference":"0x555555555065","line":13,"name":"_start","source":{"name":"_start","path":"/home/sergei/test/main.exe`_start","presentationHint":"deemphasize","sourceReference":1}}],"totalFrames":7},"command":"stackTrace","request_seq":18,"seq":0,"success":true,"type":"response"}
1751656822.432814121 (stdio) --> {"command":"dataBreakpointInfo","arguments":{"name":"a","variablesReference":1},"type":"request","seq":19}
1751656822.433374405 (stdio) <-- {"body":{"accessTypes":["read","write","readWrite"],"dataId":"7FFFFFFFDA6C/4","description":"4 bytes at 7FFFFFFFDA6C a"},"command":"dataBreakpointInfo","request_seq":19,"seq":0,"success":true,"type":"response"}
1751656826.074514151 (stdio) --> {"command":"scopes","arguments":{"frameId":524289},"type":"request","seq":20}
1751656826.075013876 (stdio) <-- {"body":{"scopes":[{"expensive":false,"name":"Locals","namedVariables":1,"presentationHint":"locals","variablesReference":1},{"expensive":false,"name":"Globals","namedVariables":0,"variablesReference":2},{"expensive":false,"name":"Registers","namedVariables":3,"presentationHint":"registers","variablesReference":3}]},"command":"scopes","request_seq":20,"seq":0,"success":true,"type":"response"}
1751656826.078428268 (stdio) --> {"command":"variables","arguments":{"variablesReference":1},"type":"request","seq":21}
1751656826.078998327 (stdio) <-- {"body":{"variables":[{"$__lldb_extensions":{"declaration":{"column":9,"line":7,"path":"/home/sergei/test/main.cpp"},"value":"2"},"declarationLocationReference":10,"evaluateName":"b","id":5,"memoryReference":"0x7FFFFFFFDA8C","name":"b","type":"int","value":"2","variablesReference":0}]},"command":"variables","request_seq":21,"seq":0,"success":true,"type":"response"}
1751656828.276206255 (stdio) --> {"command":"dataBreakpointInfo","arguments":{"name":"b","variablesReference":1},"type":"request","seq":22}
1751656828.276531219 (stdio) <-- {"body":{"accessTypes":["read","write","readWrite"],"dataId":"7FFFFFFFDA8C/4","description":"4 bytes at 7FFFFFFFDA8C b"},"command":"dataBreakpointInfo","request_seq":22,"seq":0,"success":true,"type":"response"}
1751656830.185382843 (stdio) --> {"command":"scopes","arguments":{"frameId":524290},"type":"request","seq":23}
1751656830.186013460 (stdio) <-- {"body":{"scopes":[{"expensive":false,"name":"Locals","namedVariables":1,"presentationHint":"locals","variablesReference":1},{"expensive":false,"name":"Globals","namedVariables":0,"variablesReference":2},{"expensive":false,"name":"Registers","namedVariables":3,"presentationHint":"registers","variablesReference":3}]},"command":"scopes","request_seq":23,"seq":0,"success":true,"type":"response"}
1751656830.190769672 (stdio) --> {"command":"variables","arguments":{"variablesReference":1},"type":"request","seq":24}
1751656830.191405535 (stdio) <-- {"body":{"variables":[{"$__lldb_extensions":{"declaration":{"column":9,"line":13,"path":"/home/sergei/test/main.cpp"},"value":"3"},"declarationLocationReference":12,"evaluateName":"c","id":6,"memoryReference":"0x7FFFFFFFDAAC","name":"c","type":"int","value":"3","variablesReference":0}]},"command":"variables","request_seq":24,"seq":0,"success":true,"type":"response"}
1751656831.617709160 (stdio) --> {"command":"dataBreakpointInfo","arguments":{"name":"c","variablesReference":1},"type":"request","seq":25}
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1751656833.738955975 (stdio) --> {"command":"scopes","arguments":{"frameId":524291},"type":"request","seq":26}
1751656833.739639997 (stdio) <-- {"body":{"scopes":[{"expensive":false,"name":"Locals","namedVariables":0,"presentationHint":"locals","variablesReference":1},{"expensive":false,"name":"Globals","namedVariables":0,"variablesReference":2},{"expensive":false,"name":"Registers","namedVariables":3,"presentationHint":"registers","variablesReference":3}]},"command":"scopes","request_seq":26,"seq":0,"success":true,"type":"response"}
1751656833.745048523 (stdio) --> {"command":"variables","arguments":{"variablesReference":1},"type":"request","seq":27}
1751656833.745321989 (stdio) <-- {"body":{"variables":[]},"command":"variables","request_seq":27,"seq":0,"success":true,"type":"response"}
1751656840.133133650 (stdio) --> {"command":"dataBreakpointInfo","arguments":{"name":"a","variablesReference":1},"type":"request","seq":28}
1751656840.133486271 (stdio) <-- {"body":{"dataId":null,"description":"variable not found: a"},"command":"dataBreakpointInfo","request_seq":28,"seq":0,"success":true,"type":"response"}
1751657715.515811443 (stdio) --> {"command":"breakpointLocations","arguments":{"source":{"name":"main.cpp","path":"/home/sergei/test/main.cpp"},"line":3},"type":"request","seq":29}
1751657715.552375793 (stdio) <-- {"body":{"breakpoints":[{"column":12,"line":3}]},"command":"breakpointLocations","request_seq":29,"seq":0,"success":true,"type":"response"}

[DrSergei]

Video example:

[llvmbot]

@llvm/issue-subscribers-lldb-dap

Author: None (DrSergei)

I found problem with `DataBreakpointInfo` request when user change selected frame a lot. VSCode doesn’t send repeated `Scopes` requests for a frame, so the frame from the last `Scopes` request is selected even after changing frames in the UI. This causes problems with `DataBreakpointInfo` requests because lldb-dap cannot find variables in this frame. I think the solution is to add frameId to scope's variables reference, allowing scopes from different frames to be distinguished.

[da-viper]

The problem is that the variableReferences for scopes is fixed.

llvm-project/lldb/tools/lldb-dap/Variables.h

Lines 16 to 19 in 567d164

	#define VARREF_FIRST_VAR_IDX (int64_t)4
	#define VARREF_LOCALS (int64_t)1
	#define VARREF_GLOBALS (int64_t)2
	#define VARREF_REGS (int64_t)3

Lifetime of Objects References
Some complex structural objects such as scopes or variables are not returned directly with their containers (stack frames, scopes, variables), but must be retrieved with separate scopes and variables requests based on object references. An object reference is an integer in the open interval (0, 231) assigned to objects by the debug adapter.

To simplify the management of object references in debug adapters, their lifetime is limited to the current suspended state. Once execution resumes, object references become invalid and DAP clients must not use them.

So when the client request a new scope. it reuses the previous variablesReference for the last frame. instead of creating a new variablesReference.

llvm-project/lldb/tools/lldb-dap/Handler/ScopesRequestHandler.cpp

Lines 88 to 92 in b293c8b

	std::vector scopes = {CreateScope("Locals", VARREF_LOCALS,
	dap.variables.locals.GetSize(), false),
	CreateScope("Globals", VARREF_GLOBALS,
	dap.variables.globals.GetSize(), false),
	CreateScope("Registers", VARREF_REGS,

The way to fix it would be to create new variablesReferences for the scopes ( Local, Global and Reg) for each frame.