From 69ab5edb4d601611ba7b4d05e56689d4b60ca3b1 Mon Sep 17 00:00:00 2001 From: Sergio Durigan Junior 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 It is possible to trigger this failure with gdb.base/foll-fork.exp (in which case a bunch of ERROR's will be printed), but one can also use the test below. Consider the following example program: #include int main (int argc, char *argv[]) { fork (); return 0; } 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 no 'inferior' associated with it, which means that 'inf == NULL'. 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. 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. This has been regtested using BuildBot and no regressions were found. gdb/ChangeLog: 2018-01-29 Sergio Durigan Junior * remote.c (remote_follow_fork): Don't call "detach_inferior". --- gdb/ChangeLog | 4 ++++ gdb/remote.c | 1 - 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index c42200571e1..12c18749efd 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,7 @@ +2018-01-29 Sergio Durigan Junior + + * remote.c (remote_follow_fork): Don't call "detach_inferior". + 2018-01-28 Simon Marchi * dwarf2read.c (free_dwo_files): Add forward-declaration. diff --git a/gdb/remote.c b/gdb/remote.c index 5ac84df0a08..74d18f7b17e 100644 --- a/gdb/remote.c +++ b/gdb/remote.c @@ -5206,7 +5206,6 @@ remote_follow_fork (struct target_ops *ops, int follow_child, child_pid = ptid_get_pid (child_ptid); remote_detach_pid (child_pid); - detach_inferior (child_pid); } } return 0; -- 2.30.2