I've added this as issue 230808.1. https://dwarfstd.org/issues/230808.1.html
-cary On Tue, Aug 8, 2023 at 9:02 AM Robinson, Paul via Dwarf-discuss <dwarf-discuss@lists.dwarfstd.org> wrote: > > # Error: DW_OP_entry_value description and examples > > ## Overview > > DW_OP_entry_value provides a way to compute a value as if the value > had been computed on entry to the current subprogram. Its operand is > either a DWARF expression, which assumes nothing is already on the > DWARF stack and leaves one value on the DWARF stack; or, it is a > register location description, and the content of the register (as it > was on entry to the subprogram) is implicitly read and pushed on the > DWARF stack. The register location description is simply a more compact > representation of the common case of reading a register; for example, > the producer can emit "DW_OP_reg1" instead of "DW_OP_breg1 0" with the > same result. > > However, the description and examples aren't completely consistent, and > in some cases are wrong. This proposal corrects the language and examples. > > ## Proposed Changes > > ### Section 2.5.1.7 Special Operations, p.37 > > The first sentence of the description of DW_OP_entry_value reads: > > The DW_OP_entry_value operation pushes the value that the described > location held upon entering the current subprogram. > > A DWARF expression does not describe a location, so this should read: > > The DW_OP_entry_value operation evaluates an expression or register > location description as if it had been evaluated upon entering the > current subprogram, and pushes the value of the expression or content > of the register, respectively. > > ### Appendix D.1.3, pp.291-292 > > There are six examples of DW_OP_entry_value, some of which are not > consistent with the description and some of which are just plain wrong. > The six examples are: > > DW_OP_entry_value 2 DW_OP_breg1 0 > DW_OP_entry_value 1 DW_OP_reg1 > DW_OP_entry_value 2 DW_OP_breg1 0 DW_OP_stack_value > DW_OP_entry_value 1 DW_OP_reg1 DW_OP_stack_value > DW_OP_entry_value 3 DW_OP_breg4 16 DW_OP_deref DW_OP_stack_value > DW_OP_entry_value 1 DW_OP_reg5 DW_OP_plus_uconst 16 > > The first two illustrate the smaller expression allowed by the special > case for a register location description; they are fine. > > The third is just wrong and should be deleted. DW_OP_stack_value converts > a memory location description into a value, but what precedes it is not > a memory location description. Without the stack_value, it's identical to > the first example. > > The fourth is just wrong and should be deleted. DW_OP_reg1 names a register > but pushes nothing on the stack, so DW_OP_stack_value is incorrect; and > without that, it's identical to the second example. > > The fifth should not have DW_OP_stack_value at the end; the expression > already leaves a value on the stack. > > The sixth is incorrectly using DW_OP_reg5, which is allowed in a location > description but not in a simple DWARF expression. The expression could be: > DW_OP_entry_value 2 DW_OP_breg5 16 > > The textual description of the sixth example should also be revised. > Currently it reads: > The address of the memory location is calculated by adding 16 to the > value contained in register 5 upon erringing the current subprogram. > <i>Note that unlike the previous DW_OP_entry_value examples, this one > does not end with DW_OP_stack_value.</i> > > This should be changed to: > Add 16 to the value register 5 had upon entering the current subprogram > and push the result. > > (The italicized text after the sixth example should be removed entirely; > there is no reason ever to use DW_OP_stack_value in these expressions.) > > -- > Dwarf-discuss mailing list > Dwarf-discuss@lists.dwarfstd.org > https://lists.dwarfstd.org/mailman/listinfo/dwarf-discuss -- Dwarf-discuss mailing list Dwarf-discuss@lists.dwarfstd.org https://lists.dwarfstd.org/mailman/listinfo/dwarf-discuss
