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Re: [Regression] Segfault on native-extended-gdbserver + fork
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.
> 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/
>
> 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.
and it's good to me.
Thanks,
Pedro Alves