From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 4365B3858039 for ; Wed, 9 Mar 2022 12:23:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 4365B3858039 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-479-Lj2q7w0EMdGnIfQQuRW9FA-1; Wed, 09 Mar 2022 07:23:24 -0500 X-MC-Unique: Lj2q7w0EMdGnIfQQuRW9FA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 19A681091DA0; Wed, 9 Mar 2022 12:23:23 +0000 (UTC) Received: from [10.97.116.50] (ovpn-116-50.gru2.redhat.com [10.97.116.50]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C7321842D6; Wed, 9 Mar 2022 12:23:20 +0000 (UTC) Message-ID: <3b2ab293-92d9-aa9b-bff2-3b6eaff27d59@redhat.com> Date: Wed, 9 Mar 2022 09:23:15 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [PATCH] Updated, fix reverse stepping multiple contiguous PC ranges To: Carl Love , gdb-patches@sourceware.org Cc: Rogerio Alves References: <442684e3f81aa1df073960bd45918106acefa2b9.camel@us.ibm.com> <0fbaf3783401f8aa8e76a4d3928efff46485ab8d.camel@us.ibm.com> From: Bruno Larsen In-Reply-To: <0fbaf3783401f8aa8e76a4d3928efff46485ab8d.camel@us.ibm.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-13.3 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Mar 2022 12:23:30 -0000 On 3/8/22 19:01, Carl Love wrote: > On Tue, 2022-03-08 at 17:21 -0300, Bruno Larsen wrote: > > >> >> >> Thanks for looking at this. Since I don't test on aarch64 often, I am >> not sure if I see regressions or racy testcases, but it does fix the >> issue you mentioned, and there doesn't seem to be regressions on >> x86_64 hardware. I have a few nits, but the main feedback is: could >> you add a testcase for this, using the dwarf assembler and manually >> creating contiguous PC ranges, so we can confirm that this is not >> regressed in the future on any hardware? >> >> Also, I can't approve a patch, but with the testcase this patch is >> mostly ok by me >> > > I have not writen anything in dwarf assembler in the past. Off the top > of my head, don't know how to create such a test case. It does seem > that there are the two testcases gdb.reverse/solib-precsave.exp and > gdb.reverse/solib-reverse.exp which the patch fixes. I guess the dwarf > assembly test would be similar to the C level code. > > Do you have an example of how to write dwarf assembly or a pointer to a > tutorial on writting dwarf? I have recently worked on gdb.base/until-trailing-insns.exp, that uses the dwarf assembler quite a bit to create a line table. I am not sure how one would go about making contiguous ranges, but maybe you can find something in gdb/testsuite/lib/dwarf.exp to help you. > > I will work on the two comments you had on the patch. Thanks for your > time reviewing the patch. > > Carl > > >>> ----------------------------------------------------------- >>> From: Luis Machado >>> Date: Mon, 21 Feb 2022 23:11:23 +0000 >>> Subject: [PATCH] Fix reverse stepping multiple contiguous PC ranges >>> >>> When running GDB's testsuite on aarch64-linux/Ubuntu 20.04, I >>> noticed some >>> failures in gdb.reverse/solib-precsave.exp and gdb.reverse/solib- >>> reverse.exp. >>> >>> The failure happens around the following code: >>> >>> 38 b[1] = shr2(17); /* middle part two */ >>> 40 b[0] = 6; b[1] = 9; /* generic statement, end part two >>> */ >>> 42 shr1 ("message 1\n"); /* shr1 one */ >>> >>> Normal execution: >>> >>> - step from line 1 will land on line 2. >>> - step from line 2 will land on line 3. >>> >>> Reverse execution: >>> >>> - step from line 3 will land on line 2. >>> - step from line 2 will land on line 2. >>> - step from line 2 will land on line 1. >>> >>> The problem here is that line 40 contains two contiguous but >>> distinct >>> PC ranges, like so: >>> >>> Line 40 - [0x7ec ~ 0x7f4] >>> Line 40 - [0x7f4 ~ 0x7fc] >>> >>> When stepping forward from line 2, we skip both of these ranges and >>> land on >>> line 42. When stepping backward from line 3, we stop at the start >>> PC of the >>> second (or first, going backwards) range of line 40. >>> >>> This happens because we have this check in >>> infrun.c:process_event_stop_test: >>> >>> /* When stepping backward, stop at beginning of line range >>> (unless it's the function entry point, in which case >>> keep going back to the call point). */ >>> CORE_ADDR stop_pc = ecs->event_thread->suspend.stop_pc; >>> if (stop_pc == ecs->event_thread->control.step_range_start >>> && stop_pc != ecs->stop_func_start >>> && execution_direction == EXEC_REVERSE) >>> end_stepping_range (ecs); >>> else >>> keep_going (ecs); >>> >>> Since we've reached ecs->event_thread->control.step_range_start, we >>> stop >>> stepping backwards. >>> >>> The right thing to do is to look for adjacent PC ranges for the >>> same line, >>> until we notice a line change. Then we take that as the start PC of >>> the >>> range. >>> >>> Another solution I thought about is to merge the contiguous ranges >>> when >>> we are reading the line tables. Though I'm not sure if we really >>> want to process >>> that data as opposed to keeping it as the compiler created, and >>> then working >>> around that. >>> >>> In any case, the following patch addresses this problem. >>> >>> I'm not particularly happy with how we go back in the ranges (using >>> "pc - 1"). >>> Feedback would be welcome. >>> >>> Validated on aarch64-linux/Ubuntu 20.04/18.04. >>> >>> Ubuntu 18.04 doesn't actually run into these failures because the >>> compiler >>> doesn't generate distinct PC ranges for the same line. >>> >>> gdb/ChangeLog: >>> >>> YYYY-MM-DD Luis Machado >>> >>> * infrun.c (process_event_stop_test): Handle backward >>> stepping >>> across multiple ranges for the same line. >>> * symtab.c (find_line_range_start): New function. >>> * symtab.h (find_line_range_start): New prototype. >>> >>> >>> Co-authored-by: Carl Love >>> --- >>> gdb/infrun.c | 24 +++++++++++++++++++++++- >>> gdb/symtab.c | 35 +++++++++++++++++++++++++++++++++++ >>> gdb/symtab.h | 16 ++++++++++++++++ >>> 3 files changed, 74 insertions(+), 1 deletion(-) >>> >>> diff --git a/gdb/infrun.c b/gdb/infrun.c >>> index 376a541faf6..997042d3e45 100644 >>> --- a/gdb/infrun.c >>> +++ b/gdb/infrun.c >>> @@ -6782,11 +6782,33 @@ if (ecs->event_thread- >>>> control.proceed_to_finish >>> have software watchpoints). */ >>> ecs->event_thread->control.may_range_step = 1; >>> >>> + /* When we are stepping inside a particular line range, in >>> reverse, >>> + and we are sitting at the first address of that range, we need >>> to >>> + check if this address also shows up in another line range as >>> the >>> + end address. >>> + >>> + If so, we need to check what line such a step range points to. >>> + If it points to the same line as the current step range, that >>> + means we need to keep going in order to reach the first >>> address >>> + of the line range. We repeat this until we eventually get to >>> the >>> + first address of a particular line we're stepping through. */ >>> + CORE_ADDR range_start = ecs->event_thread- >>>> control.step_range_start; >>> + if (execution_direction == EXEC_REVERSE) >>> + { >>> + gdb::optional real_range_start >>> + // = find_line_range_start (ecs->event_thread- >>>> suspend.stop_pc); >>> + = find_line_range_start (ecs->event_thread- >>>> stop_pc()); //carll fi> + >>> + >>> + if (real_range_start.has_value ()) >>> + range_start = *real_range_start; >>> + } >>> + >>> /* When stepping backward, stop at beginning of line range >>> (unless it's the function entry point, in which case >>> keep going back to the call point). */ >>> CORE_ADDR stop_pc = ecs->event_thread->stop_pc (); >>> - if (stop_pc == ecs->event_thread->control.step_range_start >>> + if (stop_pc == range_start >>> && stop_pc != ecs->stop_func_start >> >> I think this could be moved to the line above. >> >>> && execution_direction == EXEC_REVERSE) >>> end_stepping_range (ecs); >>> diff --git a/gdb/symtab.c b/gdb/symtab.c >>> index 1a39372aad0..c40739919d1 100644 >>> --- a/gdb/symtab.c >>> +++ b/gdb/symtab.c >>> @@ -3425,6 +3425,41 @@ find_pc_line (CORE_ADDR pc, int notcurrent) >>> return sal; >>> } >>> >>> +/* See symtah.h. */ >>> + >>> +gdb::optional >>> +find_line_range_start (CORE_ADDR pc) >>> +{ >>> + struct symtab_and_line current_sal = find_pc_line (pc, 0); >>> + >>> + if (current_sal.line == 0) >>> + return {}; >>> + >>> + struct symtab_and_line prev_sal = find_pc_line (current_sal.pc - >>> 1, 0); >>> + >>> + /* If the previous entry is for a different line, that means we >>> are already >>> + at the entry with the start PC for this line. */ >>> + if (prev_sal.line != current_sal.line) >>> + return current_sal.pc; >>> + >>> + /* Otherwise, keep looking for entries for the same line but >>> with >>> + smaller PC's. */ >>> + bool done = false; >>> + CORE_ADDR prev_pc; >>> + while (!done) >>> + { >>> + prev_pc = prev_sal.pc; >>> + >>> + prev_sal = find_pc_line (prev_pc - 1, 0); >>> + >>> + /* Did we notice a line change? If so, we are done with the >>> search. */ >>> + if (prev_sal.line != current_sal.line) >>> + done = true; >> >> Shouldn't prev_sal.line also be checked here and return an empty >> optional? I am not sure when that happens, so please enlighten me if >> there is no need to check. >> >>> + } >>> + >>> + return prev_pc; >>> +} >>> + >>> /* See symtab.h. */ >>> >>> struct symtab * >>> diff --git a/gdb/symtab.h b/gdb/symtab.h >>> index d12eee6e9d8..4d893a8a3b8 100644 >>> --- a/gdb/symtab.h >>> +++ b/gdb/symtab.h >>> @@ -2149,6 +2149,22 @@ extern struct symtab_and_line find_pc_line >>> (CORE_ADDR, int); >>> extern struct symtab_and_line find_pc_sect_line (CORE_ADDR, >>> struct obj_section *, >>> int); >>> >>> +/* Given PC, and assuming it is part of a range of addresses that >>> is part of a >>> + line, go back through the linetable and find the starting PC of >>> that >>> + line. >>> + >>> + For example, suppose we have 3 PC ranges for line X: >>> + >>> + Line X - [0x0 - 0x8] >>> + Line X - [0x8 - 0x10] >>> + Line X - [0x10 - 0x18] >>> + >>> + If we call the function with PC == 0x14, we want to return 0x0, >>> as that is >>> + the starting PC of line X, and the ranges are contiguous. >>> +*/ >>> + >>> +extern gdb::optional find_line_range_start (CORE_ADDR >>> pc); >>> + >>> /* Wrapper around find_pc_line to just return the symtab. */ >>> >>> extern struct symtab *find_pc_line_symtab (CORE_ADDR); >> >> > -- Cheers! Bruno Larsen