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Rozycki" , Simon Marchi Cc: Tom Tromey , gdb-patches@sourceware.org References: <20251217043141.1790384-1-simon.marchi@polymtl.ca> <87jyylyu60.fsf@tromey.com> <87fr99ymhw.fsf@tromey.com> <85958fad-17e1-4593-b842-d60a6610f149@polymtl.ca> <87jyyjmzo4.fsf@tromey.com> <5cc22d76-115f-4054-ba34-6006e6013f06@efficios.com> <02b08b9d-7478-4901-9230-0e4c6bb6d726@efficios.com> Content-Language: en-US From: Simon Marchi In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Mon, 5 Jan 2026 19:05:26 +0000 X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 2026-01-05 03:07, Maciej W. Rozycki wrote: > On Sat, 3 Jan 2026, Simon Marchi wrote: > >>>> Given a lot of this is MIPS-specific, I was hoping that Maciej could be >>>> able to help (adding in CC). >>> >>> I don't know offhand as it's stuff I haven't touched for ages now. I'll >>> see what I can do. Also I can see you've pushed your change already, so I >>> gather there's no rush. NB it was bad timing to get into this discussion >>> as I had an emergency situation to handle and overall hectic time through >>> recent weeks. >>> >>> Happy New Year for now! >> >> Thanks for replying, hope all is well for you. > > I'm fine myself, thank you, just even busier and more distracted than > usual. > >> I pushed the patch because I convinced myself that the patch wouldn't >> break the ECOFF-in-ELF case. Here is the relevant quote from my >> previous message: >> >> Ok, so I think that the consequence of my patch is that if you're >> parsing ECOFF-in-ELF, then we'll allocate minimal symbols unnecessarily >> in mdebugread's minimal_symbol_reader. They still won't get installed >> because of the check in minimal_symbol_reader::install. They will get >> freed when the minimal_symbol_reader gets destroyed. So that means >> slightly higher memory usage for the duration of >> elfmdebug_build_psymtabs, but no change in behavior. I can live with >> that, so I'll go ahead and push the patch. >> >> Of course, this is all based on my understanding, from the information I >> gleaned here and there. It seems like not many people remember this era >> nowadays :(. > > My early MIPS experience certainly overlaps with the era (even MIPS/COFF, > as in ULTRIX/MIPS), but I never got into the details back then. At least > I usually know where to look for when chasing bits now. > > The mdebug spec continues living online I believe, though it could be at > archive.org only nowadays; I can check. I have a local copy for anyone > needing it too. Yes, it does refer Third Eye Software. I dug a bit deeper and found these links. The last one is especially useful to understand the history. ECOFF spec https://web.archive.org/web/20160305114748/http://h41361.www4.hp.com/docs/base_doc/DOCUMENTATION/V50A_ACRO_SUP/OBJSPEC.PDF mdebug, on David Anderson's page https://www.prevanders.net/#mdebug mdebug spec (at least some version of it) https://www.prevanders.net/Mdebug.ps Note from Peter Rowell about mdebug http://www.datahedron.com/mips.html https://www.prevanders.net/mdebug.html (mirror) >> What would help me, if you have time (no rush), is to tell me if we can >> reasonably consider the code in mipsread.c (and mdebugread.c, which >> seems related) to be obsolete and remove it. > > As I say I'll see what I can do. Overall emitting ECOFF-in-ELF frame > unwinding information aka Procedure Description Records (PDR), a valuable > subset of the mdebug stuff, continues being supported by MIPS GCC and GAS. > No other stuff is relevant anymore; we have no support for IRIX or ULTRIX > targets left and the GNU tools can't produce other ECOFF debug information > for MIPS targets anymore. > > NB I had plans/ideas to improve PDR handling in GDB, but this has never > materialised. It's good having/improving IMHO as PDR records are very > lightweight and retained by `strip', and with its variable frame format > the MIPS target is very bad for debugging when execution is stopped at a > random place with no associated debug information, which might be libc or > suchlike. Then you just have the PC and the register stack available and > nothing else, not even the return address ($ra may have been clobbered). > > But all the PDR support is gone from GDB AFAICT and ISTR now having a > discussion as to bringing it back some 20 years ago while I was still at > MTI, possibly with Daniel Jacobowitz. The messages should be easy to > chase, but otherwise I have to conclude none of this is relevant to MIPS > targets anymore. So I guess I've figured it out for you already. Ok, thanks for the precious information. > This stuff is possibly used by the Alpha target however, though I'm not > sure offhand as I'm less familiar with the matters there. I am mostly convinced that none of this is relevant anymore. And if it ever became relevant anymore for some reason, I think it would be better to just start from scratch, given how much this has bit-rotten. Simon