From patchwork Wed Apr 13 15:53:22 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Machado X-Patchwork-Id: 11732 Received: (qmail 43567 invoked by alias); 13 Apr 2016 15:53:45 -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 43543 invoked by uid 89); 13 Apr 2016 15:53:44 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL, BAYES_00, RCVD_IN_DNSWL_NONE, SPF_PASS autolearn=ham version=3.3.2 spammy= X-HELO: relay1.mentorg.com Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Wed, 13 Apr 2016 15:53:34 +0000 Received: from svr-orw-fem-05.mgc.mentorg.com ([147.34.97.43]) by relay1.mentorg.com with esmtp id 1aqN6i-0001zm-CT from Luis_Gustavo@mentor.com for gdb-patches@sourceware.org; Wed, 13 Apr 2016 08:53:32 -0700 Received: from opsys.world.mentorg.com (147.34.91.1) by svr-orw-fem-05.mgc.mentorg.com (147.34.97.43) with Microsoft SMTP Server id 14.3.224.2; Wed, 13 Apr 2016 08:53:31 -0700 From: Luis Machado To: Subject: [PATCH v3 1/2] Debugging without a binary (regression) Date: Wed, 13 Apr 2016 10:53:22 -0500 Message-ID: <1460562803-10817-2-git-send-email-lgustavo@codesourcery.com> In-Reply-To: <1460562803-10817-1-git-send-email-lgustavo@codesourcery.com> References: <1460562803-10817-1-git-send-email-lgustavo@codesourcery.com> MIME-Version: 1.0 X-IsSubscribed: yes When we attempt to debug a process using GDBserver in standard remote mode without a symbol file on GDB's end, we may run into an issue where GDB cuts the connection attempt short due to an error. The error is caused by not being able to open a symbol file, like so: --- (gdb) set sysroot (gdb) tar rem :2345 Remote debugging using :2345 /proc/23769/exe: Permission denied. (gdb) i r The program has no registers now. (gdb) It should've been like this: (gdb) set sysroot (gdb) tar rem :2345 Remote debugging using :2345 warning: /tmp/symbol-file: Permission denied. 0xf7ddb2d0 in ?? () (gdb) i r eax 0x0 0 ecx 0x0 0 edx 0x0 0 ebx 0x0 0 esp 0xffffdfa0 0xffffdfa0 ebp 0x0 0x0 esi 0x0 0 edi 0x0 0 eip 0xf7ddb2d0 0xf7ddb2d0 eflags 0x200 [ IF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0 (gdb) This is caused by a couple of function calls within exec_file_locate_attach that can potentially throw errors. The following patch guards both exec_file_attach and symbol_file_add_main to prevent the errors from disrupting the connection process. There was also a case where native GDB tripped on this problem, but it was mostly fixed by bf74e428bca61022bd5cdf6bf28789a184748b4d. Regression-tested on x86-64/Ubuntu. Changes in v2: - We are using two TRY/CATCH blocks to guard both exec_file_attach and symbol_file_add_main. - Adjusted code to display only a single warning message if both TRY/CATCH blocks throw with the same error message. - I had to duplicate the exception message string because the second CATCH block will overwrite the contents of the pointer we saved. Changes in v3: - Fixed unitialized exception variable. - Used cleanup to free dynamically-allocated exception message. - Fixed comment typo. gdb/ChangeLog: 2016-04-13 Luis Machado * exec.c (exec_file_locate_attach): Guard a couple functions that can throw errors. (exception_print_same): New helper function. --- gdb/exec.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 58 insertions(+), 2 deletions(-) diff --git a/gdb/exec.c b/gdb/exec.c index a10ab9b..c998ab1 100644 --- a/gdb/exec.c +++ b/gdb/exec.c @@ -135,6 +135,25 @@ exec_file_clear (int from_tty) printf_unfiltered (_("No executable file now.\n")); } +/* Returns non-zero if exceptions E1 and E2 are equal. Returns zero + otherwise. */ + +static int +exception_print_same (struct gdb_exception e1, struct gdb_exception e2) +{ + const char *msg1 = e1.message; + const char *msg2 = e2.message; + + if (msg1 == NULL) + msg1 = ""; + if (msg2 == NULL) + msg2 = ""; + + return (e1.reason == e2.reason + && e1.error == e2.error + && strcmp (e1.message, e2.message) == 0); +} + /* See gdbcore.h. */ void @@ -142,6 +161,7 @@ exec_file_locate_attach (int pid, int from_tty) { char *exec_file, *full_exec_path = NULL; struct cleanup *old_chain; + struct gdb_exception prev_err = exception_none; /* Do nothing if we already have an executable filename. */ exec_file = (char *) get_exec_file (0); @@ -181,9 +201,45 @@ exec_file_locate_attach (int pid, int from_tty) } old_chain = make_cleanup (xfree, full_exec_path); + make_cleanup (free_current_contents, &prev_err.message); + + /* exec_file_attach and symbol_file_add_main may throw an error if the file + cannot be opened either locally or remotely. + + This happens for example, when the file is first found in the local + sysroot (above), and then disappears (a TOCTOU race), or when it doesn't + exist in the target filesystem, or when the file does exist, but + is not readable. + + Even without a symbol file, the remote-based debugging session should + continue normally instead of ending abruptly. Hence we catch thrown + errors/exceptions in the following code. */ + TRY + { + exec_file_attach (full_exec_path, from_tty); + } + CATCH (err, RETURN_MASK_ERROR) + { + if (err.message != NULL) + warning ("%s", err.message); + + prev_err = err; + + /* Save message so it doesn't get trashed by the catch below. */ + prev_err.message = xstrdup (err.message); + } + END_CATCH - exec_file_attach (full_exec_path, from_tty); - symbol_file_add_main (full_exec_path, from_tty); + TRY + { + symbol_file_add_main (full_exec_path, from_tty); + } + CATCH (err, RETURN_MASK_ERROR) + { + if (!exception_print_same (prev_err, err)) + warning ("%s", err.message); + } + END_CATCH do_cleanups (old_chain); }