> On Mar 17, 2017, at 2:49 PM, David Anderson <dave...@linuxmail.org> wrote: > > On 03/17/2017 01:18 PM, Adrian Prantl wrote: >> Are these two expressions equivalent? >> 1. DW_OP_breg1 0 DW_OP_breg2 0 DW_OP_plus DW_OP_stack_value >> 2. DW_OP_reg1 DW_OP_reg2 DW_OP_plus DW_OP_stack_value > > In DW4 (DW5 has same text) > These operations name a register location. To fetch the contents of a > register, it is necessary to > use one of the register based addressing operations, such as DW_OP_bregx > (see Section > 2.5.1.2). > > To me that means that 2. above cannot work.
Thanks for the clarification! To summarize in my own words: in DWARF 4+, a DW_OP_reg(x) may only appear in a register location description, which implies that it must either be the only operation in an expression, or embedded inside an expression that takes a register location description as an argument, such as DW_OP_entry_value. In particular, this means that these two location descriptions are equivalent: 1. DW_OP_breg1 0 DW_OP_stack_value ; implicit location description 2. DW_OP_reg1 ; register location description This is illegal: 1. DW_OP_reg1 DW_OP_deref And these are also equivalent: 1. DW_OP_breg1 0 DW_OP_deref DW_OP_stack_value ; implicit loc. desc. 2. DW_OP_breg1 0 ; memory loc. desc. Let me know if I got anything wrong. -- adrian > > In 1. the value of DW_OP_breg1 0 > (for example) is pushed on the stack. > > Can someone point out > where the standard (4 or 5 or?) states the push happens? > Ah yes: DW5: > > 2.5.1.2 Register Values > > The following operations push a value onto the stack > that is either the contents of a register or the result > of adding the contents of a register to a given > signed offset. DW_OP_regval_type pushes the > contents of the register together with the given > base type, while the other operations push the > result of adding the contents of a register > to a given signed offset together with the generic type. > > Notice that DW_OP_reg<n> is NOT in the list where something > gets pushed on the stack. > > Comments/correction? > DavidA. > _______________________________________________ > Dwarf-Discuss mailing list > Dwarf-Discuss@lists.dwarfstd.org > http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
