From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca (simark.ca [158.69.221.121]) by sourceware.org (Postfix) with ESMTPS id BB8193858D33 for ; Thu, 4 May 2023 17:20:27 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org BB8193858D33 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=simark.ca Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=simark.ca Received: from [172.16.0.192] (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id B04771E0D3; Thu, 4 May 2023 13:20:26 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=simark.ca; s=mail; t=1683220826; bh=/GBRYRzhcRFxCzxjtlxlGE0Qe7B1XinMab5IK7w+9tA=; h=Date:Subject:To:References:From:In-Reply-To:From; b=km5IyU2iOatVIgjJVwQnCMUQaKd1CqAnbZhHgVGF7xu67sAvxxJUGqeCuELBGRBBZ X/Jbv7fHbnw0OxTEv0C3X6HqNyD/mT7OhViJgS2TL44llpmvMYo2paGSvBbgDgOWZo oed5+x+kofvrOKs2wJAfow4vnG5PWxUewy6uJ6yM= Message-ID: <5ec7bbaa-6615-f1e0-8846-164789a1ccca@simark.ca> Date: Thu, 4 May 2023 13:20:25 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH v5 09/19] gdb: Update x86 FreeBSD architectures to support XSAVE layouts. To: John Baldwin , gdb-patches@sourceware.org References: <20230427210113.45380-1-jhb@FreeBSD.org> <20230427210113.45380-10-jhb@FreeBSD.org> <98bf6cc8-f119-b9a9-aef6-94ee366f196c@FreeBSD.org> Content-Language: fr From: Simon Marchi In-Reply-To: <98bf6cc8-f119-b9a9-aef6-94ee366f196c@FreeBSD.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,NICE_REPLY_A,SPF_HELO_PASS,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 5/3/23 19:45, John Baldwin wrote: > On 5/3/23 10:14 AM, Simon Marchi wrote: >>> @@ -285,7 +291,9 @@ i386fbsd_core_read_description (struct gdbarch *gdbarch, >>> struct target_ops *target, >>> bfd *abfd) >>> { >>> - return i386_target_description (i386fbsd_core_read_xcr0 (abfd), true); >>> + x86_xsave_layout layout; >>> + return i386_target_description (i386_fbsd_core_read_xsave_info (abfd, layout), >>> + true); >> >> Reading this gives me some questions. Just thinking out loud, nothing >> necessarily actionable at the moment >> >> I found it strange that i386_fbsd_core_read_xsave_info fills an >> x86_xsave_layout object that we don't use. We get xcr0 to generate an >> appropriate target description here, and later we'll call >> target_fetch_x86_xsave_layout (when initializing the gdbarch) to get the >> x86_xsave_layout and save it in the i386_gdbarch_tdep object. I'm >> wondering if, design-wise, this means that the target_desc object should >> carry the xsave layout information. It would be saved in the tdesc >> here, and i386_gdbarch_init would just get it from the tdesc. >> >> It's probably not as simple as that, since target descriptions are >> transferred as XML from remote targets, and you still have to consider >> older target descriptions that wouldn't include that information. But >> I'm just trying to think what the ideal design would be. > > It's kind of odd as the layout doesn't affect the set of registers that > are available (and today tdesc's are AFAICT just about which registers > the target provides). Yeah, so I'm thinking that this could be some arch-specific information in addition to the register list. > The reason I extended the existing method that reads xcr0 is that I > needed the section size along with the value of xcr0 to compute the > layout via i386_set_xsave_layout and I was trying to avoid duplicating > the code to fetch the section. I could perhaps change the function > to return the value of xcr0 and the section size instead if that is > less confusing? I don't think any change is necessary to your code, it's ok like that. >>> diff --git a/gdb/i386-fbsd-tdep.h b/gdb/i386-fbsd-tdep.h >>> index cb991af9e49..f96c00d45eb 100644 >>> --- a/gdb/i386-fbsd-tdep.h >>> +++ b/gdb/i386-fbsd-tdep.h >>> @@ -20,10 +20,16 @@ >>> #ifndef I386_FBSD_TDEP_H >>> #define I386_FBSD_TDEP_H >>> +#include "gdbsupport/x86-xstate.h" >>> #include "regset.h" >>> -/* Get XSAVE extended state xcr0 from core dump. */ >>> -extern uint64_t i386fbsd_core_read_xcr0 (bfd *abfd); >>> +/* Validate and fetch XSAVE extended state xcr0 and extended area >>> + layout from core dump. */ >>> +uint64_t i386_fbsd_core_read_xsave_info (bfd *abfd, x86_xsave_layout &layout); >> >> I was a bit confused when I read the comment above for the first time. >> Can you rephrase it to make it clear that the function returns the XSAVE >> extended state, and fills LAYOUT? >> >> Also, what does "validate" mean, what happens if the thing we validate >> is not valid? > > Hmm, the intent is "Validate and fetch xcr0 and the XSAVE layout". In > particular, this does not return the extended state (which would be the > value of all the AVX registers, etc.) but instead returns only the mask of > enabled state (xcr0) and the layout of the extended area. > > If xcr0 does not appear valid or the section doesn't seem to have a valid > size (i386_set_xsave_layout returns false) then the function claims that > only SSE is reported by returning X86_XSTATE_SSE_MASK. That is the > validation that "validate" is referring to. Maybe it's the two "and" in the sentence that make it ambiguous. So, perhaps: Read the xcr0 value from the ABFD core file. If it appears to be valid, return it and fill LAYOUT with values inferred from that value. Otherwise, return X86_XSTATE_SSE_MASK as a fallback and leave LAYOUT untouched. Simon