From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by sourceware.org (Postfix) with ESMTPS id 568D3383F842 for ; Thu, 7 May 2020 05:04:14 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 568D3383F842 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tdevries@suse.de X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id D0134ABC7; Thu, 7 May 2020 05:04:15 +0000 (UTC) Date: Thu, 7 May 2020 07:04:11 +0200 From: Tom de Vries To: gdb-patches@sourceware.org Cc: Pedro Alves Subject: [PATCH][gdb] Fix stepping over fork with follow-fork-mode child and gcc-8 Message-ID: <20200507050409.GA30601@delia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) X-Spam-Status: No, score=-19.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, KAM_NUMSUBJECT, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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: Thu, 07 May 2020 05:04:15 -0000 Hi, When running test-case gdb.threads/fork-child-threads.exp with gcc-8 instead of gcc-7, we have: ... (gdb) next^M [Attaching after Thread 0x7ffff7fae740 (LWP 27574) fork to child process \ 27578]^M [New inferior 2 (process 27578)]^M [Detaching after fork from parent process 27574]^M [Inferior 1 (process 27574) detached]^M [Thread debugging using libthread_db enabled]^M Using host libthread_db library "/lib64/libthread_db.so.1".^M [Switching to Thread 0x7ffff7fae740 (LWP 27578)]^M -main () at src/gdb/testsuite/gdb.threads/fork-child-threads.c:41^M +main () at src/gdb/testsuite/gdb.threads/fork-child-threads.c:34^M -41 i = pthread_create (&thread, NULL, start, NULL);^M +34 switch (fork ())^M -(gdb) PASS: gdb.threads/fork-child-threads.exp: next over fork +(gdb) FAIL: gdb.threads/fork-child-threads.exp: next over fork ... This is due to the fact that gcc-8 generates more precise line info, making the instruction after the call to fork a "recommended breakpoint location". However, it is a bug because next is supposed to move to the next source line. The problem is that in process_event_stop_test we hit this code: ... if ((ecs->event_thread->suspend.stop_pc == stop_pc_sal.pc) && (ecs->event_thread->current_line != stop_pc_sal.line || ecs->event_thread->current_symtab != stop_pc_sal.symtab)) { if (stop_pc_sal.is_stmt) { /* We are at the start of a different line. So stop. Note that we don't stop if we step into the middle of a different line. That is said to make things like for (;;) statements work better. */ if (debug_infrun) fprintf_unfiltered (gdb_stdlog, "infrun: stepped to a different line\n"); end_stepping_range (ecs); return; } ... because current_line and current_symtab have initial values: ... (gdb) p ecs->event_thread->current_line $8 = 0 (gdb) p ecs->event_thread->current_symtab $9 = (symtab *) 0x0 ... Fix this in follow_fork by copying current_line and current_symtab from parent thread to child thread. Tested on x86_64-linux, with gcc 7.5.0 and gcc 10.0.1. OK for trunk? Thanks, - Tom [gdb] Fix stepping over fork with follow-fork-mode child and gcc-8 gdb/ChangeLog: 2020-05-07 Tom de Vries * infrun.c (follow_fork): Copy current_line and current_symtab to child thread. --- gdb/infrun.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/gdb/infrun.c b/gdb/infrun.c index 0e1ba6986b1..3c6b201a9fc 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -681,6 +681,8 @@ follow_fork () struct breakpoint *exception_resume_breakpoint = NULL; CORE_ADDR step_range_start = 0; CORE_ADDR step_range_end = 0; + int current_line = 0; + symtab *current_symtab = NULL; struct frame_id step_frame_id = { 0 }; struct thread_fsm *thread_fsm = NULL; @@ -734,6 +736,8 @@ follow_fork () (tp->control.step_resume_breakpoint); step_range_start = tp->control.step_range_start; step_range_end = tp->control.step_range_end; + current_line = tp->current_line; + current_symtab = tp->current_symtab; step_frame_id = tp->control.step_frame_id; exception_resume_breakpoint = clone_momentary_breakpoint (tp->control.exception_resume_breakpoint); @@ -794,6 +798,8 @@ follow_fork () = step_resume_breakpoint; tp->control.step_range_start = step_range_start; tp->control.step_range_end = step_range_end; + tp->current_line = current_line; + tp->current_symtab = current_symtab; tp->control.step_frame_id = step_frame_id; tp->control.exception_resume_breakpoint = exception_resume_breakpoint;