> On Feb 25, 2020, at 5:29 PM, Levo DeLellis via lldb-dev > <lldb-dev@lists.llvm.org> wrote: > > I'm thoroughly confused so I may say incorrect thing. I don't expect any > replies to this entire post but bits would be helpful. I'll double check if > you need me to be specific since it's likely I remember or ran something > wrong. For my language I output llvm-ir directly so I may generate llvm-ir > that the llvm api does not and I may create very specific ir if I need to. > > I noticed a number of things. When I declare something with llvm.dbg.declare > it doesn't happen where I declare it but at the start of the function? I put > my alloca's at the start of the function like llvm recommends so I have > invalid pointers and invalid array sizes which causes vscode to crash. Which > is fine I'm sure I can write null and say the size is 0 before the first line > of the function.
These are really LLVM questions. Basically: - if you can see the variable with dwarfdump and it doesn't show up in LLDB, you should ask on lldb-dev - if you can't see the variable with dwarfdump, you should ask on llvm-dev A golden rule of thumb is to look at what clang is doing and copy that. The location of a dbg.declare is mostly irrelevant, since there can only be one dbg.declare per variable and it is valid throughout the entire scope. > I thought maybe I can use llvm.dbg.addr to work around the problem but I > never got it working in the way I hoped (Does it execute at the start of the > function? which explains why my unexpected results). I don't understand the question here. It would be helpful to post a minimal example, and look at the output of -print-after-all to see how it is transformed by the various passes, so you can ask a more directed question. > I manage to have some good results with llvm.dbg.value. I noticed if I put a > value in a local variable and use `llvm.dbg.value(i64 %abc` there's a high > likelihood it will have an incorrect value or will be wrong once I step > through more code. However i64 1234 always seem to work. > > How should I tell the debugger about my variables? This page says you are > "transitioning away from" llvm.dbg.declare > https://llvm.org/docs/SourceLevelDebugging.html I see llvm.dbg.addr says to > only use it once and I had some luck with llvm.dbg.value. How do I decide > when to use llvm.dbg.value vs llvm.dbg.addr? May I use llvm.dbg.value on a > variable that I didn't specific with llvm.dbg.addr? (for example a const > value in a variable that has no address)? What about an array passed in from > a function? Do I need to store the pointer and or length to a variable to > give it an address before the debugger can understand it? If your variables "live" on the stack, such as in clang -O0 code, you should use one dbg.declare per variable. Otherwise you'll need at least one dbg.value per SSA value that carries a variable value. > > Is it possible to say ignore my variable until I hit this specific? > My language uses constructors so I often have to execute code before pointers > become valid. Yes, dbg.value(undef, ...) followed by another dbg.value will do that explicitly. You can not achieve this with dbg.declare because it is global. > The language also cleans up so on a return statement as a 'hack' I execute > `br false, label %dummy123, label %dummy123, !dbg !123\ndummy123:\n` so the > user can see the variables before the cleanup happens/pointers get freed. I > mentioned earlier when using vscode having invalid array pointer and invalid > size (very large number) made vscode crash. I'm not sure what happened but I > had lldb-mi-9 take up many gb (30gb+) in some situations so it may not be a > literal crash in the process but locks up and do undesirable behavior > > I don't expect to get all the answers but maybe a piece here and there will > help. Should I continue to use llvm.dbg.declare for now with lldb 9? or > should I use llvm.dbg.addr and llvm.dbg.value? Depends on the kind of code you generate. > Should I always initialize my variables to 0? (so I don't crash vscode when > it uses lldb-mi-9) Is there a way I can say ignore this variable until I hit > line X where I know the memory will be initialized fully? Do I need to worry > about the order I initialize variables or the order I call llvm.dbg.addr? (I > remember, call llvm.dbg.addr once per variable) > > Thank you for reading and thank you for any help > > _______________________________________________ > lldb-dev mailing list > lldb-dev@lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
