From patchwork Fri Jan 29 13:11:39 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Antoine Tremblay X-Patchwork-Id: 10667 Received: (qmail 83661 invoked by alias); 29 Jan 2016 13:11:46 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Delivered-To: mailing list gdb-patches@sourceware.org Received: (qmail 82836 invoked by uid 89); 29 Jan 2016 13:11:45 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-0.9 required=5.0 tests=BAYES_00, KAM_LAZY_DOMAIN_SECURITY autolearn=no version=3.3.2 spammy=4907, Antoine, 490, 7, 498, 7 X-HELO: usplmg20.ericsson.net Received: from usplmg20.ericsson.net (HELO usplmg20.ericsson.net) (198.24.6.45) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-SHA encrypted) ESMTPS; Fri, 29 Jan 2016 13:11:43 +0000 Received: from EUSAAHC006.ericsson.se (Unknown_Domain [147.117.188.90]) by usplmg20.ericsson.net (Symantec Mail Security) with SMTP id 2D.5E.06940.3226BA65; Fri, 29 Jan 2016 13:59:15 +0100 (CET) Received: from [142.133.110.95] (147.117.188.8) by smtp-am.internal.ericsson.com (147.117.188.92) with Microsoft SMTP Server id 14.3.248.2; Fri, 29 Jan 2016 08:11:40 -0500 Subject: Re: [PATCH] gdb.trace: Remove struct tracepoint_action_ops. To: =?UTF-8?Q?Marcin_Ko=c5=9bcielnicki?= , Pedro Alves , References: <1453577516-19252-1-git-send-email-koriakin@0x04.net> <56A60CD3.6060704@redhat.com> <56A61255.8020503@0x04.net> From: Antoine Tremblay Message-ID: <56AB650B.1000204@ericsson.com> Date: Fri, 29 Jan 2016 08:11:39 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <56A61255.8020503@0x04.net> X-IsSubscribed: yes On 01/25/2016 07:17 AM, Marcin Kościelnicki wrote: > On 25/01/16 12:53, Pedro Alves wrote: >> On 01/23/2016 07:31 PM, Marcin Kościelnicki wrote: >>> The struct tracepoint_action has an ops field, pointing to >>> a tracepoint_action_ops structure, containing send and download ops. >>> However, this field is only present when compiled in gdbserver, and not >>> when compiled in IPA. When gdbserver is downloading tracepoint actions >>> to IPA, it skips offsetof(struct tracepoint_action, type) bytes from >>> its struct tracepoint_action, to get to the part that corresponds to >>> IPA's struct tracepoint_action. >>> >>> Unfortunately, this fails badly on ILP32 platforms where alignof(long >>> long) >>> == 8. Consider struct collect_memory_action layout in gdbserver: >>> >>> 0-3: base.ops >>> 4: base.type >>> 8-15: addr >>> 16-23: len >>> 24-27: basereg >>> sizeof == 32 >>> >>> and its layout in IPA: >>> >>> 0: base.type >>> 8-15: addr >>> 16-23: len >>> 24-27: basereg >>> sizeof == 32 >>> >>> When gdbserver tries to download it to IPA, it skips the first 4 bytes >>> (base.ops), figuring the rest will match what IPA expects - which is >>> not true, since addr is aligned to 8 bytes and will be at a different >>> relative position to base.type. >>> >>> The problem went unnoticed on the currently supported platforms, since >>> aarch64 and x86_64 have ops aligned to 8 bytes, and i386 has only 4-byte >>> alignment for long long. >>> >>> There are a few possible ways around this problem. I decided on >>> removing >>> ops altogether, since they can be easily inlined in their (only) places >>> of use - in fact allowing us share the code between 'L' and 'R'. Any >>> approach where struct tracepoint_action is different between IPA and >>> gdbserver is just asking for trouble. >>> >>> Found on s390. Tested on x86_64, s390, s390x. >> >> Hmm, this is essentially the same as: >> >> https://sourceware.org/ml/gdb-patches/2015-03/msg00995.html >> >> Right? >> >> Seems that other patch inlines things a bit less though, which offhand >> looks preferable. WDYT? >> >> Not sure what happened to that series. I thought most of it (if not all) >> had been approved already. >> >> Thanks, >> Pedro Alves >> > > Huh, I didn't know about that patch series. Good to know, since I was > going to try doing ppc tracepoints next, and had no idea that has > already been attempted. What happened to that patchset/author? Kind of > strange to abandon mostly-finished code when there's a $3k bounty on it. > > The other patch looks fine too, I have no preference here. > > Marcin Kościelnicki I had the same problem on ARM. We could just keep the struct and pack it too, this is common for ABIs IMO... It would avoid this kind of mistake in the future if we were going to reintroduce something similar... I had this patch in the pipeline: Author: Antoine Tremblay Date: Thu Jan 28 13:03:10 2016 -0500 Fix structure alignment problems with IPA protocol objects. While testing fast tracepoints on ARM I came across this problem : Program received signal SIGSEGV, Segmentation fault. 0x4010b56c in ?? () from target:/lib/arm-linux-gnueabihf/libc.so.6 (gdb) FAIL: gdb.trace/ftrace.exp: ond globvar > 7: continue The problem is that on GDBServer side struct tracepoint_action is aligned on 4 bytes, and collect_memory_action is aligned on 8. However in the IPA they are both aligned on 8 bytes. Thus when we copy the data from GDBServer's struct tracepoint_action->type offset to the ipa the alignement is wrong and the addr,len,basereg values are wrong also, causing a crash in the inferiror as it tries to read memory at a bogus address. This patch fixes this issue by setting the tracepoint_action and collect_memory_action as packed. This patch also fixes this issue in general by setting all IPA protocol object structures as packed. gdb/gdbserver/ChangeLog: * tracepoint.c (ATTR_PACKED): Moved earlier in the file. (struct tracepoint_action): Use ATTR_PACKED. (struct collect_memory_action): Likewise. (struct collect_registers_action): Likewise. (struct eval_expr_action): Likewise. (struct collect_static_trace_data_action): Likewise. struct tracepoint_action; @@ -490,7 +498,7 @@ struct tracepoint_action const struct tracepoint_action_ops *ops; #endif char type; -}; +} ATTR_PACKED; /* An 'M' (collect memory) action. */ struct collect_memory_action @@ -500,14 +508,14 @@ struct collect_memory_action ULONGEST addr; ULONGEST len; int32_t basereg; -}; +} ATTR_PACKED; /* An 'R' (collect registers) action. */ struct collect_registers_action { struct tracepoint_action base; -}; +} ATTR_PACKED; /* An 'X' (evaluate expression) action. */ @@ -516,13 +524,13 @@ struct eval_expr_action struct tracepoint_action base; struct agent_expr *expr; -}; +} ATTR_PACKED; /* An 'L' (collect static trace data) action. */ struct collect_static_trace_data_action { struct tracepoint_action base; -}; +} ATTR_PACKED; #ifndef IN_PROCESS_AGENT static CORE_ADDR @@ -828,14 +836,6 @@ IP_AGENT_EXPORT_VAR struct trace_state_variable *trace_state_variables; when the wrapped-around trace frame is the one being discarded; the free space ends up in two parts at opposite ends of the buffer. */ -#ifndef ATTR_PACKED -# if defined(__GNUC__) -# define ATTR_PACKED __attribute__ ((packed)) -# else -# define ATTR_PACKED /* nothing */ -# endif -#endif - /* The data collected at a tracepoint hit. This object should be as small as possible, since there may be a great many of them. We do not need to keep a frame number, because they are all sequential WDYT ? Thanks, Antoine diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c index 33f6120..35ce2ad 100644 --- a/gdb/gdbserver/tracepoint.c +++ b/gdb/gdbserver/tracepoint.c @@ -467,6 +467,14 @@ static int write_inferior_data_ptr (CORE_ADDR where, CORE_ADDR ptr); #endif +#ifndef ATTR_PACKED +# if defined(__GNUC__) +# define ATTR_PACKED __attribute__ ((packed)) +# else +# define ATTR_PACKED /* nothing */ +# endif +#endif + /* Operations on various types of tracepoint actions. */