From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 32980 invoked by alias); 7 Feb 2019 17:02:58 -0000 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 Received: (qmail 32968 invoked by uid 89); 7 Feb 2019 17:02:58 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,SPF_PASS autolearn=ham version=3.3.2 spammy=steal X-HELO: mx2.freebsd.org Received: from mx2.freebsd.org (HELO mx2.freebsd.org) (8.8.178.116) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 07 Feb 2019 17:02:56 +0000 Received: from mx1.freebsd.org (mx1.freebsd.org [96.47.72.80]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client CN "mx1.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx2.freebsd.org (Postfix) with ESMTPS id 406A865BDF; Thu, 7 Feb 2019 17:02:54 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from smtp.freebsd.org (smtp.freebsd.org [IPv6:2610:1c1:1:606c::24b:4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 11D536A87E; Thu, 7 Feb 2019 17:02:53 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from John-Baldwins-MacBook-Pro-3.local (ralph.baldwin.cx [66.234.199.215]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) (Authenticated sender: jhb) by smtp.freebsd.org (Postfix) with ESMTPSA id 89AD619DD; Thu, 7 Feb 2019 17:02:52 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Subject: Re: [PATCH 5/9] Add a helper function to resolve TLS variable addresses for FreeBSD. To: Simon Marchi Cc: gdb-patches@sourceware.org References: <94e3c18ecfd67945d21926299a30dbde@polymtl.ca> From: John Baldwin Openpgp: preference=signencrypt Message-ID: <1c8c6e25-376e-5e27-b189-a35ce9b0ce3e@FreeBSD.org> Date: Thu, 07 Feb 2019 17:02:00 -0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <94e3c18ecfd67945d21926299a30dbde@polymtl.ca> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 11D536A87E X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-2.97 / 15.00]; local_wl_from(0.00)[FreeBSD.org]; NEURAL_HAM_MEDIUM(-1.00)[-0.996,0]; NEURAL_HAM_SHORT(-0.98)[-0.979,0]; NEURAL_HAM_LONG(-1.00)[-0.999,0]; ASN(0.00)[asn:11403, ipnet:2610:1c1:1::/48, country:US] X-IsSubscribed: yes X-SW-Source: 2019-02/txt/msg00068.txt.bz2 On 2/6/19 9:04 PM, Simon Marchi wrote: > On 2019-01-24 12:08, John Baldwin wrote: >> On 1/22/19 10:42 AM, John Baldwin wrote: >>> The fbsd_get_thread_local_address function accepts the base address of >>> a thread's DTV array and the base address of an object file's link map >>> and uses this to compute a TLS variable's address. FreeBSD >>> architectures use an architecture-specific method to determine the >>> address of the DTV array pointer and call this helper function to >>> perform the rest of the address calculation. >>> >>> * fbsd-tdep.c (fbsd_pspace_data_handle): New variable. >>> (struct fbsd_pspace_data): New type. >>> (get_fbsd_pspace_data, fbsd_pspace_data_cleanup) >>> (fbsd_read_integer_by_name, fbsd_fetch_rtld_offsets) >>> (fbsd_get_tls_index, fbsd_get_thread_local_address): New function. >>> (_initialize_fbsd_tdep): Initialize 'fbsd_pspace_data_handle'. >>> * fbsd-tdep.c (fbsd_get_thread_local_address): New prototype. >>> --- >>> gdb/ChangeLog | 10 ++++ >>> gdb/fbsd-tdep.c | 146 >>> ++++++++++++++++++++++++++++++++++++++++++++++++ >>> gdb/fbsd-tdep.h | 10 ++++ >>> 3 files changed, 166 insertions(+) >>> >>> diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c >>> index d971d3a653..2e0f72d17b 100644 >>> --- a/gdb/fbsd-tdep.c >>> +++ b/gdb/fbsd-tdep.c >>> + >>> +/* Lookup offsets of fields in the runtime linker's 'Obj_Entry' >>> + structure needed to determine the TLS index of an object file. */ >>> + >>> +static void >>> +fbsd_fetch_rtld_offsets (struct gdbarch *gdbarch, struct >>> fbsd_pspace_data *data) >>> +{ >>> + TRY >>> + { >>> + /* Fetch offsets from debug symbols in rtld. */ >>> + data->off_linkmap = parse_and_eval_long ("&((Obj_Entry >>> *)0)->linkmap"); >>> + data->off_tlsindex = parse_and_eval_long ("&((Obj_Entry >>> *)0)->tlsindex"); >>> + data->rtld_offsets_valid = true; >>> + return; >> >> I'm not really happy about using parse_and_eval_long with an open-coded >> equivalent of offsetof() here. It seems we don't already have existing >> functionality for this though? I think I could use 'lookup_struct' to >> find >> the 'struct type *' for 'Obj_Entry', but if I used >> 'lookup_struct_elt_type' >> to get the type of an element that doesn't give me anything that has >> the >> offset. We could perhaps instead add a new function >> 'lookup_struct_elt_offset' >> that took the element name as a string and figured out the offset. We >> could >> then use this to provide an 'offsetof' builtin for the C language >> perhaps. >> However, I suspect that lookup_struct_elt_offset would have to invoke a >> language-specific function to do the actual computation (just as ptype >> /o >> handling is language-specific). > > Doesn't parse_and_eval_long also call in language-specific things? The > expression is parsed according to whatever is the current language, I > suppose. If needed, I guess we could change temporarily the current > language to C, which is the language the dynamic linker is written in > (until proven otherwise). Mmm, that's true. > The offset of fields within structures is available (see macro > FIELD_BITPOS). I haven't looked too deep into it, but it sounds like it > should be possible to implement what you need with that. Hmm. When I looked at the code for ptype /o it seemed to keep a running tally for the byte offset. It wasn't clear to me if perhaps FIELD_BITPOS was for bitfields and the bit offset within a byte/word. However, the Linux kernel patch series does have some code to do this. I could perhaps steal from that to implement lookup_struct_elt_offset. I would probably make it support nested fields as well (I think the Linux kernel patches are using it for some nested fields). > One question: does this work only when you have debug info for the > dynamic linker data structures? Will debug info always be available? > On some Linux distributions, for example, I think it's rather common to > not have the debug info for the system libraries (libc, libpthread) by > default. Yes, this requires debug symbols. Recent releases of FreeBSD do include an option to install them by default, but they are not always present. I will probably add global variables in rtld itself similar to the ones inside of the thread library and then update GDB to fetch those instead once I've done that. I just haven't patched the runtime linker yet for that. -- John Baldwin                                                                            Â