From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 54010 invoked by alias); 4 Jul 2018 13:36:35 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 53987 invoked by uid 89); 4 Jul 2018 13:36:34 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,HTML_MESSAGE,RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.2 spammy=HX-Google-Smtp-Source:AAOMgpc, H*c:alternative X-HELO: mail-oi0-f67.google.com Received: from mail-oi0-f67.google.com (HELO mail-oi0-f67.google.com) (209.85.218.67) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 04 Jul 2018 13:36:30 +0000 Received: by mail-oi0-f67.google.com with SMTP id k81-v6so10771055oib.4 for ; Wed, 04 Jul 2018 06:36:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ndmsystems-com.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=3/8xoSWJSLaX60ygIbzOYqFFBJxubpsvhfUU0TJSSoc=; b=JaWQDuN8UtgHePhHVa/1z9bxnjcbTbicsf43CnXm+YjQTFhA4eTLeOd2g3CK6p9LSi YXpVKwUxeCt84okpcNe6yVzZMKwLx6/CTI2fSDdlUqFTaR3MPXMiSA83NeFGz8rOKeR+ 0u8c+W4UmH5Tkfayp+6un8okOZPKUUmNeWyuQaCKdei2MWqa1L96+haJzOx/BjNE1UZd hx6MS0jTedN0f05Nk5TxCifOQ9vgODsuir8PXSFXPzDMm1AV2SBt7ZqcMMIV7rJM2ahE 5TwIGfkA+LoE77WA9f9H+AsnYZgB1UIgOSH7JPs0iRXDZ+9fnl7Upk0s2FXCKiJN/cKN DBLQ== MIME-Version: 1.0 Received: by 2002:a9d:4b83:0:0:0:0:0 with HTTP; Wed, 4 Jul 2018 06:35:48 -0700 (PDT) In-Reply-To: <20180703193753.GC2675@embecosm.com> References: <20180703193753.GC2675@embecosm.com> From: Sergey Korolev Date: Wed, 04 Jul 2018 13:36:00 -0000 Message-ID: Subject: Re: [PATCH] MIPS/GDB/linux-nat.c: Fix a child detach condition for uClibc-ng To: Andrew Burgess Cc: gdb-patches@sourceware.org Content-Type: text/plain; charset="UTF-8" X-IsSubscribed: yes X-SW-Source: 2018-07/txt/msg00086.txt.bz2 Andrew, thanks for your feedback. I agree that your explanation and variable names are more descriptive. I tested your patch in my environment and did not see any problems. On Tue, Jul 3, 2018 at 10:37 PM, Andrew Burgess wrote: > * Sergey Korolev [2018-06-15 01:54:12 +0300]: > > > Current implementation expects that WIFSTOPPED (W_STOPCODE (0)) is true, > > but in the uClibc-ng it is false on MIPS. The patch adds a "detach" > > helper variable to avoid this corner case: WIFSTOPPED applied > > only to a status filled by a waitpid call that should never return > > the status with zero stop signal. > > I took a quick look through this patch, and have a little feedback. > > You might want to expand your commit message to explain _why_ MIPS is > different (having a signal 127), I didn't know this, and it puzzled me > for a while as to why your above text didn't just indicate a bug in > uClibc-ng :) > > > --- > > gdb/linux-nat.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c > > index 445b59fa4a..916de2d335 100644 > > --- a/gdb/linux-nat.c > > +++ b/gdb/linux-nat.c > > @@ -468,6 +468,7 @@ linux_nat_target::follow_fork (int follow_child, int > > detach_fork) > > /* Detach new forked process? */ > > if (detach_fork) > > { > > + int detach = 1; > > There's already a detach_fork variable in this function, so maybe a > more descriptive name would make thing clearer. > > > struct cleanup *old_chain = make_cleanup (delete_lwp_cleanup, > > child_lp); > > > > @@ -492,9 +493,11 @@ linux_nat_target::follow_fork (int follow_child, int > > detach_fork) > > perror_with_name (_("Couldn't do single step")); > > if (my_waitpid (child_pid, &status, 0) < 0) > > perror_with_name (_("Couldn't wait vfork process")); > > + else > > + detach = WIFSTOPPED (status); > > } > > > > - if (WIFSTOPPED (status)) > > + if (detach) > > { > > int signo; > > I wonder if we should move the status into the scope of the call to > WIFSTOPPED, and avoid making any calls on it unless we know it has > been filled in. > > Such a thing might look like this: > > > [PATCH] gdb: Avoid using W_STOPCODE(0) as this is ambiguous on MIPS > > The MIPS target supports 127 signals, and this can create an ambiguity > in process wait statuses. A status value of 0x007f could potentially > indicate a process that has exited with signal 127, or a process that > has stopped with signal 0. > > In uClibc-ng the interpretation of 0x007f is that the process has > exited with signal 127 rather than stopped with signal 0, and so, > WIFSTOPPED (W_STOPCODE (0)) will be false rather than true as it would > be on most other platforms. > > Given that it's pretty easy to avoid using W_STOPCODE (0), lets do that. > > gdb/ChangeLog: > > * linux-nat.c (linux_nat_target::follow_fork): Avoid using > 'W_STOPCODE (0)' as this could be ambiguous. > --- > gdb/ChangeLog | 6 ++++++ > gdb/linux-nat.c | 15 +++++++++++---- > 2 files changed, 17 insertions(+), 4 deletions(-) > > diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c > index af38a2a1a5b..4de19770f42 100644 > --- a/gdb/linux-nat.c > +++ b/gdb/linux-nat.c > @@ -448,7 +448,6 @@ linux_nat_target::follow_fork (int follow_child, int > detach_fork) > if (!follow_child) > { > struct lwp_info *child_lp = NULL; > - int status = W_STOPCODE (0); > int has_vforked; > ptid_t parent_ptid, child_ptid; > int parent_pid, child_pid; > @@ -468,6 +467,8 @@ linux_nat_target::follow_fork (int follow_child, int > detach_fork) > /* Detach new forked process? */ > if (detach_fork) > { > + int child_stop_signal = 0; > + bool detach_child = true; > struct cleanup *old_chain = make_cleanup (delete_lwp_cleanup, > child_lp); > > @@ -487,18 +488,24 @@ linux_nat_target::follow_fork (int follow_child, int > detach_fork) > if (!gdbarch_software_single_step_p (target_thread_architecture > (parent_ptid))) > { > + int status; > + > linux_disable_event_reporting (child_pid); > if (ptrace (PTRACE_SINGLESTEP, child_pid, 0, 0) < 0) > perror_with_name (_("Couldn't do single step")); > if (my_waitpid (child_pid, &status, 0) < 0) > perror_with_name (_("Couldn't wait vfork process")); > + else > + { > + detach_child = WIFSTOPPED (status); > + child_stop_signal = WSTOPSIG (status); > + } > } > > - if (WIFSTOPPED (status)) > + if (detach_child) > { > - int signo; > + int signo = child_stop_signal; > > - signo = WSTOPSIG (status); > if (signo != 0 > && !signal_pass_state (gdb_signal_from_host (signo))) > signo = 0; > -- > 2.14.4 > >