> On Oct 12, 2018, at 9:53 AM, Adrian Prantl <apra...@apple.com> wrote: > > > >> On Oct 11, 2018, at 11:16 AM, Greg Clayton via lldb-dev >> <lldb-dev@lists.llvm.org> wrote: >> >> DWARF5 finally added the ability to track what each value means on the >> expression stack. Prior to DWARF 5, we had no idea what each entry on the >> expression value stack was (file address, load address >> (Value::eValueTypeLoadAddress), plain value (Value::eValueTypeScalar). We >> have tracked this info for a while now, but the DWARF5 spec is much more >> specific on how things should be treated. > > Greg, > > I'd like to summarize my own understanding of how this works — could you take > a look and correct me where I'm wrong? > > - The only way to push a file address onto the DWARF stack is a DW_OP_addr. > > The decision of whether a value pushed onto the DWARF stack is a scalar or a > load address depends on the location kind (cf. DWARF 5, section 2.6 "Location > Descriptions"): > - A register location description (DW_OP_reg.*) reads the register contents > and pushes a scalar. > - An implicit location description (.* (DW_OP_implicit_.*|DW_OP_stack_value) > yields a scalar after evaluating the expression. > - A memory location description (anything else, such as DW_OP_breg) yields a > load address. > (- composite locations, like DW_OP_piece are handled according to these rules > for each piece) > > Practically speaking, I think this means that a DW_OP_(f)breg always turns > into a load address (as it can only appear in an implicit or a memory > location), and a DW_OP_reg always. turns into a scalar. > > > Is that what LLDB is doing, and if not, could that explain at least some of > the failures that Davide is seeing?
Correct! Summarizing: - DW_OP_addr == file address - DW_OP_(f)breg == load address - DW_OP_reg == scalar - DW_OP_deref(x) == needs to be fixed to change to scalar, currently leaves it as load addr - DW_OP_const == scalar (unless DW_OP_piece is used) The failure Davide is seeing is there is a load address on the stack, and after the deref, it gets pushed the correct value but leaves it as a load addr. When any expression is done being evaluated, we look at the type of that value that is left at the top of the stack. If it is a load addr, then we read from memory if it is a scalar, it is the value itself Issue Davide is running into is the value is correct, but the type is still load addr incorrectly. Greg _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
