(re-sending because outlook omitted the group address) > -----Original Message----- > From: Dwarf-Discuss <dwarf-discuss-boun...@lists.dwarfstd.org> On Behalf > Of Jakub Jelinek via Dwarf-Discuss > Sent: Tuesday, March 9, 2021 10:16 AM > To: Andrew Cagney <andrew.cag...@gmail.com> > Cc: DWARF Discussion <dwarf-discuss@lists.dwarfstd.org> > Subject: Re: [Dwarf-Discuss] compilers generating ABI non-compliant > function calls? > > On Tue, Mar 09, 2021 at 10:05:04AM -0500, Andrew Cagney via Dwarf-Discuss > wrote: > > Is anyone aware of a compiler doing this (I figure with LTO there's a > > strong incentive)? And if so, how is this described to the debugger. > > The ABI / calling-convention is no longer on hand for filling in the > > blanks. > > Sure, GCC does that. On many architectures, IPA-RA might keep data > live across a function call even in registers that are per the ABI > officially call clobbered (if it can prove the particular callee does not > clobber it). This isn't expressed in DWARF I believe.
DWARF doesn't describe clobbering or non-clobbering; it describes where values live. If something gets clobbered by a call, the location list should reflect that the location changes (or doesn't exist) as of the instruction after the call; if it doesn't get clobbered, the location range should correctly span the call instruction. The debugger does not need to know the ABI in order to trust that location lists are correct. The producer is responsible for emitting correct location lists that don't depend on ABI knowledge by the consumer. AFAIK the main reason to annotate a subprogram with a calling convention is so that a debugger can manufacture a call correctly, in response to a user command. It might also be necessary to identify the location of the return value, as someone else mentioned. --paulr > > On x86, GCC can use different register calling conventions for local > functions (basically automatic regparm and/or sseregparm calling > conventions > when possible). I think this is reflected in the debug info, the > DW_TAG_formal_parameter locations should match those. > > Jakub > > _______________________________________________ > Dwarf-Discuss mailing list > Dwarf-Discuss@lists.dwarfstd.org > https://urldefense.com/v3/__http://lists.dwarfstd.org/listinfo.cgi/dwarf- > discuss- > dwarfstd.org__;!!JmoZiZGBv3RvKRSx!saJXjJCyJzGPm7PNYMIYGGdh4Ox2WiUfnoR9uFea > -PrVPbcUNCuNYk9zgwlQJrcZ9Q$ _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
