From owner-freebsd-current@FreeBSD.ORG Mon Feb 6 21:20:21 2012 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6ECFF1065673 for ; Mon, 6 Feb 2012 21:20:21 +0000 (UTC) (envelope-from dmitrym@juniper.net) Received: from exprod7og122.obsmtp.com (exprod7og122.obsmtp.com [64.18.2.22]) by mx1.freebsd.org (Postfix) with ESMTP id EC8BB8FC12 for ; Mon, 6 Feb 2012 21:20:20 +0000 (UTC) Received: from P-EMHUB03-HQ.jnpr.net ([66.129.224.36]) (using TLSv1) by exprod7ob122.postini.com ([64.18.6.12]) with SMTP ID DSNKTzBEEttUxkE/WnrnHjVv91PrzYEDCpD9@postini.com; Mon, 06 Feb 2012 13:20:21 PST Received: from magenta.juniper.net (172.17.27.123) by P-EMHUB03-HQ.jnpr.net (172.24.192.33) with Microsoft SMTP Server (TLS) id 8.3.213.0; Mon, 6 Feb 2012 13:19:31 -0800 Received: from [172.24.26.191] (dmitrym-lnx.jnpr.net [172.24.26.191]) by magenta.juniper.net (8.11.3/8.11.3) with ESMTP id q16LJV128863; Mon, 6 Feb 2012 13:19:31 -0800 (PST) (envelope-from dmitrym@juniper.net) Message-ID: <4F3043E2.6090607@juniper.net> Date: Mon, 6 Feb 2012 13:19:30 -0800 From: Dmitry Mikulin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111229 Thunderbird/9.0 MIME-Version: 1.0 To: Konstantin Belousov References: <749E238A-A85F-4264-9DEB-BCE1BBD21C9D@juniper.net> <20120125074824.GD2726@deviant.kiev.zoral.com.ua> <4F2094B4.70707@juniper.net> <20120126122326.GT2726@deviant.kiev.zoral.com.ua> <4F22E8FD.6010201@juniper.net> <20120129074843.GL2726@deviant.kiev.zoral.com.ua> <4F26E0D1.8040100@juniper.net> <20120130192727.GZ2726@deviant.kiev.zoral.com.ua> <4F2C756A.80900@juniper.net> <20120204204218.GC3283@deviant.kiev.zoral.com.ua> In-Reply-To: <20120204204218.GC3283@deviant.kiev.zoral.com.ua> Content-Type: multipart/mixed; boundary="------------000108040008060709070606" X-EXCLAIMER-MD-CONFIG: e4081efb-6d29-443c-8708-750833aec629 X-Mailman-Approved-At: Mon, 06 Feb 2012 21:27:55 +0000 Cc: freebsd-current Current , Marcel Moolenaar Subject: Re: [ptrace] please review follow fork/exec changes X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Feb 2012 21:20:21 -0000 --------------000108040008060709070606 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit > I see what is going on. The wait loop for P_PPWAIT in do_fork() simply > do not allow the ptracestop() in the syscall return path to be reached. > There seems to be more problems. In particular, I do not see anything > which would prevent the child from being reapped while the loop is > executing (assume that the parent is multithreaded and other thread > processed SIGCHLD and called wait). > > Lets deal with these bugs after your proposal for interface changes is > dealt with. OK. > > Yes, I agree with the proposal to add flag to the child lwp info. > I think it will be easier if the flag is different from PL_FLAG_FORKED. > I named it PL_FLAG_CHILD. > > PT_FOLLOW_EXEC is easy to implement, but my question is, how can debugger > operate (correctly) if it ignores exec events ? After exec, the whole > cached state of the debuggee must be invalidated, and since debugger > ignores the notification when the invalidation shall be done, it probably > gets very confused. You're right, the debugger needs to handle exec() events implicitly when it starts up executables. The problem is that there is OS-independent machinery in gdb which handles statup fork-exec sequence differently from when the debuggee itself does an exec(). Basically in the event handling code I need to be able to distinguish app startup by gdb from an exec done by the app. Other OS-es have flags like PL_FLAG_EXEC set on demand: they have an equivalent of PT_FOLLOW_EXEC. I attached a modified patch that solves the problem. It tries to separate the always-on TDB_EXEC from the on-demand TDB_FOLLOWEXEC without changing existing functionality. Let me know if it's acceptable. Another issue I'm investigating is that after the switch-over to the child gdb gets a SIGHUP when it continues the child. I think it has to do with the re-parenting/orphan business. I'll let you know what I find, but if you have an idea what might be causing it, please let me know. Thanks. Dmitry. --------------000108040008060709070606 Content-Type: text/x-patch; name="follow-exec-2.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="follow-exec-2.diff" Index: kern/kern_exec.c =================================================================== --- kern/kern_exec.c (revision 231088) +++ kern/kern_exec.c (working copy) @@ -890,6 +890,8 @@ exec_fail_dealloc: if (error == 0) { PROC_LOCK(p); td->td_dbgflags |= TDB_EXEC; + if (p->p_flag & P_FOLLOWEXEC) + td->td_dbgflags |= TDB_FOLLOWEXEC; PROC_UNLOCK(p); /* Index: kern/kern_fork.c =================================================================== --- kern/kern_fork.c (revision 231088) +++ kern/kern_fork.c (working copy) @@ -1035,7 +1035,9 @@ fork_return(struct thread *td, struct trapframe *f p->p_oppid = p->p_pptr->p_pid; proc_reparent(p, dbg); sx_xunlock(&proctree_lock); + td->td_dbgflags |= TDB_CHILD; ptracestop(td, SIGSTOP); + td->td_dbgflags &= ~TDB_CHILD; } else { /* * ... otherwise clear the request. Index: kern/sys_process.c =================================================================== --- kern/sys_process.c (revision 231088) +++ kern/sys_process.c (working copy) @@ -660,6 +660,7 @@ kern_ptrace(struct thread *td, int req, pid_t pid, case PT_TO_SCX: case PT_SYSCALL: case PT_FOLLOW_FORK: + case PT_FOLLOW_EXEC: case PT_DETACH: sx_xlock(&proctree_lock); proctree_locked = 1; @@ -873,6 +874,12 @@ kern_ptrace(struct thread *td, int req, pid_t pid, else p->p_flag &= ~P_FOLLOWFORK; break; + case PT_FOLLOW_EXEC: + if (data) + p->p_flag &= ~P_FOLLOWEXEC; + else + p->p_flag |= P_FOLLOWEXEC; + break; case PT_STEP: case PT_CONTINUE: @@ -936,7 +943,8 @@ kern_ptrace(struct thread *td, int req, pid_t pid, p->p_sigparent = SIGCHLD; } p->p_oppid = 0; - p->p_flag &= ~(P_TRACED | P_WAITED | P_FOLLOWFORK); + p->p_flag &= ~(P_TRACED | P_WAITED | P_FOLLOWFORK | + P_FOLLOWEXEC); /* should we send SIGCHLD? */ /* childproc_continued(p); */ @@ -1141,10 +1149,14 @@ kern_ptrace(struct thread *td, int req, pid_t pid, pl->pl_flags |= PL_FLAG_SCX; if (td2->td_dbgflags & TDB_EXEC) pl->pl_flags |= PL_FLAG_EXEC; + if (td2->td_dbgflags & TDB_FOLLOWEXEC) + pl->pl_flags |= PL_FLAG_FOLLOWEXEC; if (td2->td_dbgflags & TDB_FORK) { pl->pl_flags |= PL_FLAG_FORKED; pl->pl_child_pid = td2->td_dbg_forked; } + if (td2->td_dbgflags & TDB_CHILD) + pl->pl_flags |= PL_FLAG_CHILD; pl->pl_sigmask = td2->td_sigmask; pl->pl_siglist = td2->td_siglist; strcpy(pl->pl_tdname, td2->td_name); Index: kern/subr_syscall.c =================================================================== --- kern/subr_syscall.c (revision 230847) +++ kern/subr_syscall.c (working copy) @@ -216,7 +216,8 @@ syscallret(struct thread *td, int error, struct sy ((td->td_dbgflags & (TDB_FORK | TDB_EXEC)) != 0 || (p->p_stops & S_PT_SCX) != 0)) ptracestop(td, SIGTRAP); - td->td_dbgflags &= ~(TDB_SCX | TDB_EXEC | TDB_FORK); + td->td_dbgflags &= + ~(TDB_SCX | TDB_EXEC | TDB_FOLLOWEXEC | TDB_FORK); PROC_UNLOCK(p); } } Index: sys/proc.h =================================================================== --- sys/proc.h (revision 231088) +++ sys/proc.h (working copy) @@ -384,6 +384,8 @@ do { \ process */ #define TDB_STOPATFORK 0x00000080 /* Stop at the return from fork (child only) */ +#define TDB_CHILD 0x00000100 /* New child indicator for ptrace() */ +#define TDB_FOLLOWEXEC 0x00000200 /* follow exec(2) */ /* * "Private" flags kept in td_pflags: @@ -613,6 +615,7 @@ struct proc { #define P_HWPMC 0x800000 /* Process is using HWPMCs */ #define P_JAILED 0x1000000 /* Process is in jail. */ +#define P_FOLLOWEXEC 0x2000000 /* Do not report execs with ptrace. */ #define P_INEXEC 0x4000000 /* Process is in execve(). */ #define P_STATCHILD 0x8000000 /* Child process stopped or exited. */ #define P_INMEM 0x10000000 /* Loaded into memory. */ Index: sys/ptrace.h =================================================================== --- sys/ptrace.h (revision 231088) +++ sys/ptrace.h (working copy) @@ -64,6 +64,7 @@ #define PT_SYSCALL 22 #define PT_FOLLOW_FORK 23 +#define PT_FOLLOW_EXEC 24 #define PT_GETREGS 33 /* get general-purpose registers */ #define PT_SETREGS 34 /* set general-purpose registers */ @@ -106,7 +107,9 @@ struct ptrace_lwpinfo { #define PL_FLAG_SCX 0x08 /* syscall leave point */ #define PL_FLAG_EXEC 0x10 /* exec(2) succeeded */ #define PL_FLAG_SI 0x20 /* siginfo is valid */ -#define PL_FLAG_FORKED 0x40 /* new child */ +#define PL_FLAG_FORKED 0x40 /* child born */ +#define PL_FLAG_CHILD 0x80 /* I am from child */ +#define PL_FLAG_FOLLOWEXEC 0x100 /* follow exec(2) */ sigset_t pl_sigmask; /* LWP signal mask */ sigset_t pl_siglist; /* LWP pending signal */ struct __siginfo pl_siginfo; /* siginfo for signal */ --------------000108040008060709070606--