From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 2806 invoked by alias); 17 May 2012 21:02:43 -0000 Received: (qmail 2790 invoked by uid 22791); 17 May 2012 21:02:41 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=AWL,BAYES_00,KHOP_THREADED,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from sibelius.xs4all.nl (HELO glazunov.sibelius.xs4all.nl) (83.163.83.176) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 17 May 2012 21:02:28 +0000 Received: from glazunov.sibelius.xs4all.nl (kettenis@localhost [127.0.0.1]) by glazunov.sibelius.xs4all.nl (8.14.5/8.14.3) with ESMTP id q4HL1xdG031866; Thu, 17 May 2012 23:01:59 +0200 (CEST) Received: (from kettenis@localhost) by glazunov.sibelius.xs4all.nl (8.14.5/8.14.3/Submit) id q4HL1vAW013600; Thu, 17 May 2012 23:01:57 +0200 (CEST) Date: Thu, 17 May 2012 21:02:00 -0000 Message-Id: <201205172101.q4HL1vAW013600@glazunov.sibelius.xs4all.nl> From: Mark Kettenis To: yao@codesourcery.com CC: brobecker@adacore.com, gdb-patches@sourceware.org, cltang@codesourcery.com In-reply-to: <4FB308F4.50602@codesourcery.com> (message from Yao Qi on Wed, 16 May 2012 09:55:00 +0800) Subject: Re: [PATCH 1/4] New gdb arch hook: return_with_first_hidden_param_p References: <1334755073-26528-1-git-send-email-yao@codesourcery.com> <20120503011435.GA3294@adacore.com> <4FA22D7B.1040707@codesourcery.com> <20120504175830.GQ15555@adacore.com> <4FA743EC.1080903@codesourcery.com> <20120507201345.GX15555@adacore.com> <4FAA2D25.4060700@codesourcery.com> <20120510212054.GA5886@adacore.com> <4FACEB4B.1060603@codesourcery.com> <20120514171453.GL10253@adacore.com> <4FB1FCD2.5070302@codesourcery.com> <201205151802.q4FI2O2Y013475@glazunov.sibelius.xs4all.nl> <4FB308F4.50602@codesourcery.com> Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2012-05/txt/msg00671.txt.bz2 > Date: Wed, 16 May 2012 09:55:00 +0800 > From: Yao Qi > > On 05/16/2012 02:02 AM, Mark Kettenis wrote: > >> > No, the extra hidden parameter's type is the reference of the function's > >> > return type. My point is if we only examine debug info, we don't know > >> > whether hidden parameter is passed, because the debug info is the same > >> > regardless of hidden parameter is passed or not. > > I'm still very confused. This "hidden parameter" thing sounds exactly > > like "struct_return". So are you saying that on some architectures > > gdbarch_return_value() return RETUN_VALUE_REGISTER_CONVENTION when if > > fact for C++ (and not for plain C) it should return > > RETURN_VALUE_STRUCT_CONVENTION? > > In an inferior call, there are two steps related to ABI, 1) passing > parameters, 2) fetching return value. The "hidden parameter" is > relevant to both steps. Your description above is correct, and it is > about step 2. No, that's not quite correct. push_dummy_call() gets passed a "struct return" argument, so it is also about step 1. Except that this decision is unconditionally bypassed for GNU v3 C++ ABI because of the language_pass_by_reference() check. > My patches are trying to fix the problems in step 1. So > far, GDB passes hidden parameter for some language, but on some targets, > the hidden parameter is not passed by parameter register, it is passed > by other register specified by its ABI. GDB is wrong if it still pass > hidden parameter to parameter register. But the proper place to take that decision is in gnu-v3-abi.c:gnuv3_pass_by_reference(), since this problem is rather specific to the C++ ABI used by GCC. So I think you need a gnuv3_pass_by_reference() gdbarch hook, and call that if it is it is installed. It's easy to do that, since get_type_arch() on the type passed as an argument to gnuv3_pass_by_reference() function will give you the gdbarch. I think that would be far less confusing.