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authorPedro Alves <palves@redhat.com>2020-01-10 20:05:41 +0000
committerPedro Alves <palves@redhat.com>2020-01-10 20:05:41 +0000
commit873657b9e824943ae44c12966c29cbbcd21c986f (patch)
tree151b26a7c25ecb41375900ae9cdf52eeef701a4f /gdb/inferior.c
parent7f0ae84c80aae6fe8f7573343fe1ab455d18b5d8 (diff)
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Preserve selected thread in all-stop w/ background execution
In non-stop mode, if you resume the program in the background (with "continue&", for example), then gdb makes sure to not switch the current thread behind your back. That means that you can be sure that the commands you type apply to the thread you selected, even if some other thread that was running in the background hits some event just while you're typing. In all-stop mode, however, if you resume the program in the background, gdb let's the current thread switch behind your back. This is bogus, of course. All-stop and non-stop background resumptions should behave the same. This patch fixes that, and adds a testcase that exposes the bad behavior in current master. The fork-running-state.exp changes are necessary because that preexisting testcase was expecting the old behavior: Before: continue & Continuing. (gdb) [Attaching after process 8199 fork to child process 8203] [New inferior 2 (process 8203)] info threads Id Target Id Frame 1.1 process 8199 "fork-running-st" (running) * 2.1 process 8203 "fork-running-st" (running) (gdb) After: continue & Continuing. (gdb) [Attaching after process 24660 fork to child process 24664] [New inferior 2 (process 24664)] info threads Id Target Id Frame * 1.1 process 24660 "fork-running-st" (running) 2.1 process 24664 "fork-running-st" (running) (gdb) Here we see that before this patch GDB switches current inferior to the new inferior behind the user's back, as a side effect of handling the fork. The delete_exited_threads call in inferior_appeared is there to fix an issue that Baris found in a previous version of this patch. The fetch_inferior_event change increases the refcount of the current thread, and in case the fetched inferior event denotes a thread exit, the thread will not be deleted right away. A non-deleted but exited thread stays in the inferior's thread list. This, in turn, causes the "init_thread_list" call in inferior.c to be skipped. A consequence is that the global thread ID counter is not restarted if the current thread exits, and then the inferior is restarted: (gdb) start Temporary breakpoint 1 at 0x4004d6: file main.c, line 21. Starting program: /tmp/main Temporary breakpoint 1, main () at main.c:21 21 foo (); (gdb) info threads -gid Id GId Target Id Frame * 1 1 process 16106 "main" main () at main.c:21 (gdb) c Continuing. [Inferior 1 (process 16106) exited normally] (gdb) start Temporary breakpoint 2 at 0x4004d6: file main.c, line 21. Starting program: /tmp/main Temporary breakpoint 2, main () at main.c:21 21 foo (); (gdb) info threads -gid Id GId Target Id Frame * 1 2 process 16138 "main" main () at main.c:21 ^^^ Notice that GId == 2 above. It should have been "1" instead. The new tids-git-reset.exp testcase exercises the problem above. gdb/ChangeLog: 2020-01-10 Pedro Alves <palves@redhat.com> * gdbthread.h (scoped_restore_current_thread) <dont_restore, restore, m_dont_restore>: Declare. * thread.c (thread_alive): Add assertion. Return bool. (switch_to_thread_if_alive): New. (prune_threads): Switch inferior/thread. (print_thread_info_1): Switch thread before calling target methods. (scoped_restore_current_thread::restore): New, factored out from ... (scoped_restore_current_thread::~scoped_restore_current_thread): ... this. (scoped_restore_current_thread::scoped_restore_current_thread): Add assertion. (thread_apply_all_command, thread_select): Use switch_to_thread_if_alive. gdb/testsuite/ChangeLog: 2020-01-10 Pedro Alves <palves@redhat.com> * gdb.base/fork-running-state.exp (do_test): Adjust expected output. * gdb.threads/async.c: New. * gdb.threads/async.exp: New. * gdb.multi/tids-gid-reset.c: New. * gdb.multi/tids-gid-reset.exp: New.
Diffstat (limited to 'gdb/inferior.c')
-rw-r--r--gdb/inferior.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/gdb/inferior.c b/gdb/inferior.c
index e0c2ab2..9882925 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -247,6 +247,7 @@ inferior_appeared (struct inferior *inf, int pid)
{
/* If this is the first inferior with threads, reset the global
thread id. */
+ delete_exited_threads ();
if (!any_thread_p ())
init_thread_list ();