I see. It's not the end of the world because I can just parse the whole line table when requested. It's just that in PDB-land the format is such that a) I know the exact address of the prologue and epilogue at the time I parse the function record, and b) When parsing the line table, I can quickly scan to the address range for the function making the whole table parsing less efficient than necessary. But it's definitely sufficient.
On Mon, Oct 8, 2018 at 12:41 PM Jim Ingham <jing...@apple.com> wrote: > A single sequence in the line table needs to be run from beginning to end > to make sense of it. It doesn't really have addresses, it generally has a > start address, then a sequence of "increment line, increment address" > instructions. So you have to run the state machine to figure out what the > addresses are. > > However, the line table does not have to be one continuous sequence. The > DWARF docs state this explicitly, and there is an "end_sequence" > instruction to implement this. I can't see any reason why you couldn't get > the compiler to emit line tables in per-function sequences, and have the > debugger optimize reading the line table by first scanning for sequence > ends to get the map of chunks -> addresses, and then reading the line table > in those chunks. I don't think anybody does this, however. clang emitted > the whole CU as one sequence in the few examples I had sitting around. > > Jim > > > > On Oct 8, 2018, at 12:28 PM, Leonard Mosescu via lldb-dev < > lldb-dev@lists.llvm.org> wrote: > > > > Even if we do need to parse the line table, could it be done just for > the function in question? The debug info tells us the function's address > range, so is there some technical reason why it couldn't parse the line > table only for the given address range? > > > > My understanding is that there's one DWARF .debug_line "program" per CU, > and normally you'd need to "execute" the whole line number program. > > > > On Sat, Oct 6, 2018 at 8:05 PM, Zachary Turner via lldb-dev < > lldb-dev@lists.llvm.org> wrote: > > While implementing native PDB support I noticed that LLDB is asking to > parse an entire compile unit's line table in order to determine if 1 > address is a function prologue or epilogue. > > > > Is this necessary in DWARF-land? It would be nice if I could just pass > the prologue and epilogue byte size directly to the constructor of the > lldb_private::Function object when I construct it. > > > > It seems unnecessary to parse the entire line table just to set a > breakpoint by function name, but this is what ends up happening. > > > > Even if we do need to parse the line table, could it be done just for > the function in question? The debug info tells us the function's address > range, so is there some technical reason why it couldn't parse the line > table only for the given address range? > > > > _______________________________________________ > > lldb-dev mailing list > > lldb-dev@lists.llvm.org > > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev > > > > > > _______________________________________________ > > lldb-dev mailing list > > lldb-dev@lists.llvm.org > > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev > >
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