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Re: [Regression] Segfault on native-extended-gdbserver + fork
On Monday, January 29 2018, Pedro Alves wrote:
> On 01/29/2018 05:36 PM, Sergio Durigan Junior wrote:
>> From 4a37d08ca6c1aec7f47e2278b0fe78a0038eb9ee Mon Sep 17 00:00:00 2001
>> From: Sergio Durigan Junior <sergiodj@redhat.com>
>> Date: Mon, 29 Jan 2018 12:29:21 -0500
>> Subject: [PATCH] Don't call "detach_inferior" on "remote_follow_fork"
>>
>> This patch fixes a regression that has been introduced by:
>>
>> commit bc09b0c14fb713a9aec25e09b78499f3bc2441b5
>> Date: Fri Jan 19 11:48:11 2018 -0500
>>
>> Make linux_nat_detach/thread_db_detach use the inferior parameter
>>
>> Consider the following example program:
>>
>> #include <unistd.h>
>>
>> int
>> main (int argc, char *argv[])
>> {
>> fork ();
>>
>> return 0;
>> }
>>
>
> Please also mention gdb.base/foll-fork.exp.
Done.
>> When running it under gdbserver:
>>
>> # ./gdb/gdbserver/gdbserver --multi --once :2345
>>
>> And debugging it under GDB, we see a segmentation fault:
>>
>> # ./gdb/gdb -q -batch -ex 'set remote exec-file ./a.out' -ex 'tar extended-remote :2345' -ex r ./a.out
>> Starting program:
>> ...
>> [Detaching after fork from child process 16102.]
>> Segmentation fault (core dumped)
>>
>> The problem happens on inferior.c:detach_inferior:
>>
>> void
>> detach_inferior (inferior *inf)
>> {
>> /* Save the pid, since exit_inferior_1 will reset it. */
>> int pid = inf->pid;
>> ^^^^^^^^^
>>
>> exit_inferior_1 (inf, 0);
>>
>> if (print_inferior_events)
>> printf_unfiltered (_("[Inferior %d detached]\n"), pid);
>> }
>>
>> When this code is called from remote.c:remote_follow_fork, the PID is
>> valid but there is not 'inferior' associated with it, which means that
>> 'inf == NULL'.
>
> s/there is not/there is no/
Fixed.
>>
>> The proper fix here is to not call "detach_inferior" when doing remote
>> follow-fork, because we don't have an inferior to detach on the host
>> side.
>
> Add something like this here:
>
> Before bc09b0c1, that call was already a nop (exit_inferior_1 bails
> out early if you pass it a NULL inferior), except that it printed
> "Inferior PID detached" when "set print inferior-events" is on.
> Since native debugging doesn't call detach_inferior in this case,
> removing the call from remote aligns remote debugging output
> with native debugging output further.
Added.
> and it's good to me.
Pushed.
69ab5edb4d601611ba7b4d05e56689d4b60ca3b1
Thanks,
--
Sergio
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