From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 1541 invoked by alias); 14 Mar 2011 14:52:36 -0000 Received: (qmail 1532 invoked by uid 22791); 14 Mar 2011 14:52:35 -0000 X-SWARE-Spam-Status: No, hits=-1.9 required=5.0 tests=AWL,BAYES_00,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mail.codesourcery.com (HELO mail.codesourcery.com) (38.113.113.100) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 14 Mar 2011 14:52:30 +0000 Received: (qmail 3352 invoked from network); 14 Mar 2011 14:52:28 -0000 Received: from unknown (HELO scottsdale.localnet) (pedro@127.0.0.2) by mail.codesourcery.com with ESMTPA; 14 Mar 2011 14:52:28 -0000 From: Pedro Alves To: gdb@sourceware.org Subject: Re: Non-stop mode disfunctional ? Date: Mon, 14 Mar 2011 14:52:00 -0000 User-Agent: KMail/1.13.5 (Linux/2.6.35-27-generic; KDE/4.6.1; x86_64; ; ) Cc: "Chris Hall" References: <014b01cbe252$f0f736c0$d2e5a440$@highwayman.com> In-Reply-To: <014b01cbe252$f0f736c0$d2e5a440$@highwayman.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201103141452.25262.pedro@codesourcery.com> X-IsSubscribed: yes Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org X-SW-Source: 2011-03/txt/msg00097.txt.bz2 On Monday 14 March 2011 14:20:11, Chris Hall wrote: > > Sorry to follow up my own posting... It'd be better to not start a new thread for each post. > ... I'm hoping to discover if the fact that non-stop doesn't work is > (a) because I'm not using it correctly, or (b) a well known problem I > should know about, or (c) an actual bug, or (d) something else ? I only read your original post diagonally, but I'd suspect a problem with displaced-stepping. Try with both non-stop and target-async off (the default), but enabling "set breakpoint always-inserted on", and "set displaced-stepping on". -- Pedro Alves > > Thanks, > > Chris > > > -----Original Message----- > > From: gdb-owner@sourceware.org [mailto:gdb-owner@sourceware.org] On > > Behalf Of Chris Hall > > Sent: 07 March 2011 11:01 > > To: gdb@sourceware.org > > Subject: SIGSEGV on exit from subroutines -- problem with non-stop ? > > > > Hi, > > > > I am using gdb 7.2-14.fc14 to work on a large multi-threaded > > application, in C, x86-64. > > > > I have .gdbinit, per the book: > > > > set target async 1 > > set pagination off > > set non-stop on > > > > When I step using 's' or 'n', as it leaves some subroutines I keep > > getting SIGSEGV, such as: > > > > Program received signal SIGSEGV, Segmentation fault. > > signal_set (signo=Cannot access memory at address > > 0xffffffffffffff5c) > > at ... > > > > When I 'disass' the current instruction is a leaveq. Examining the > > registers I observe that rbp is zero, which is clearly nonsense. > > > > I found one instance which was repeatable, which happened to be > > before > > any threads were started: if I 'ni' through a particular function, > > it > > gets to the leaveq, and gets stuck there. Each time I do ni, the > > rsp > > and the rbp are updated by the repeated leaveq, until it goes bang. > > > > So... I began to think this isn't something complicated to do with > > multiple threads... so here is a test: > > > > <<--test.c----------------------------------------------- > > #include > > #include > > > > static void > > target(const char* message) { > > printf("%s ...BANG!\n", message) ; > > } > > > > int main(int argc, char* argv[]) { > > > > target("Light the blue touch paper") ; > > > > return 0 ; > > } > > ------------------------------------------------------->> > > > > Compiled by gcc 4.5.1 "-g -O0". > > > > If I do "gdb test", stepping by "n": > > > > <<------------------------------------------------------- > > (gdb) show non-stop > > Controlling the inferior in non-stop mode is on. > > (gdb) b target > > Breakpoint 1 at 0x4004d0: file test.c, line 6. > > (gdb) run > > Starting program: ...........test > > > > Breakpoint 1, target (message=0x400615 "Light the blue touch paper") > > at test.c:6 > > 6 printf("%s ...BANG!\n", message) ; > > (gdb) n > > Light the blue touch paper ...BANG! > > 7 } > > (gdb) n > > > > Program received signal SIGSEGV, Segmentation fault. > > target (message=Cannot access memory at address 0xfffffffffffffff8 > > ) at test.c:7 > > 7 } > > (gdb) info reg > > .... > > rbp 0x0 0x0 > > rsp 0x7fffffffe248 0x7fffffffe248 > > .... > > rip 0x4004e9 0x4004e9 > > .... > > ------------------------------------------------------->> > > > > Or, stepping by 'ni': > > > > <<------------------------------------------------------- > > (gdb) show non-stop > > Controlling the inferior in non-stop mode is on. > > (gdb) b target > > Breakpoint 1 at 0x4004d0: file test.c, line 6. > > (gdb) disass target > > Dump of assembler code for function target: > > 0x00000000004004c4 <+0>: push %rbp > > 0x00000000004004c5 <+1>: mov %rsp,%rbp > > 0x00000000004004c8 <+4>: sub $0x10,%rsp > > 0x00000000004004cc <+8>: mov %rdi,-0x8(%rbp) > > 0x00000000004004d0 <+12>: mov $0x400608,%eax > > 0x00000000004004d5 <+17>: mov -0x8(%rbp),%rdx > > 0x00000000004004d9 <+21>: mov %rdx,%rsi > > 0x00000000004004dc <+24>: mov %rax,%rdi > > 0x00000000004004df <+27>: mov $0x0,%eax > > 0x00000000004004e4 <+32>: callq 0x4003b8 > > 0x00000000004004e9 <+37>: leaveq > > 0x00000000004004ea <+38>: retq > > End of assembler dump. > > (gdb) disp/i $pc > > (gdb) run > > Starting program: .......test > > > > Breakpoint 1, target (message=0x400615 "Light the blue touch paper") > > at test.c:6 > > 6 printf("%s ...BANG!\n", message) ; > > ..... > > 1: x/i $pc > > => 0x4004e4 : callq 0x4003b8 > > (gdb) ni > > Light the blue touch paper ...BANG! > > 7 } > > 1: x/i $pc > > => 0x4004e9 : leaveq > > (gdb) ni > > target (message=0x100000000
) at > > test.c:7 > > 7 } > > 1: x/i $pc > > => 0x4004e9 : leaveq > > (gdb) ni > > Cannot access memory at address 0x8 > > (gdb) ni > > The program is not being run. > > ------------------------------------------------------->> > > > > I note that if I turn off the "non-stop" option, it works. So this > > is > > something to do with debugging multi-threaded ! > > > > I note also that if I change the target to: > > > > static int > > target(const char* message) { > > printf("%s ...BANG!\n", message) ; > > return 0 ; > > } > > > > the problem goes away... so one extra instruction between the callq > > and the leaveq makes a difference: > > > > 0x00000000004004dc <+24>: mov %rax,%rdi > > 0x00000000004004df <+27>: mov $0x0,%eax > > 0x00000000004004e4 <+32>: callq 0x4003b8 > > 0x00000000004004e9 <+37>: mov $0x0,%eax > > 0x00000000004004ee <+42>: leaveq > > 0x00000000004004ef <+43>: retq > > > > This goes some way to explaining why it appeared to be a sporadic > > problem. > > > > Is this me, or is this a bug ? It used to work :-( > > > > Thanks, > > > > Chris > >