From 80d82c196402f6a61aa84452104b9aaed364eb42 Mon Sep 17 00:00:00 2001 From: Joel Brobecker Date: Mon, 23 Nov 2015 09:56:23 -0800 Subject: [PATCH] [LynxOS] GDBserver crash debugging threaded program This crash is observable by debugging a threaded program on LynxOS. On the GDB side, this is what we would see: % gdb q (gdb) target remote machine:4444 (gdb) break q.adb:6 (gdb) cont [gdb hits breakpoint] (gdb) cont Remote connection closed <<<--- expected: [Inferior 1 (Remote target) exited normally] On the gdbserver side, which was launched as usual: % gdbserver --once :4444 q Segmentation fault (core dumped) Ooops! The problem happens while GDB is trying to handle the thread termination event of the thread that hit the breakpoint. It started happening after the following change was made: commit 96e7a1eb6d09fda9e22e112e35e7d0085a8f4fd0 Date: Fri Oct 16 11:08:38 2015 -0400 Subject: gdbserver: Reset current_thread when the thread is removed. Reset current_thread and make sure 'remove_process' is used after all associated threads have been removed first. More precisely: . GDBserver receives the execution-resume order; . lynx-low resumes it succesfully, and then relies on lynx_wait_1 to wait for the next event; . We quickly receive one, which lynx_wait_1 analyzes to be a "thread exit" event, and therefore does... case SIGTHREADEXIT: remove_thread (find_thread_ptid (new_ptid)); lynx_continue (new_ptid); goto retry; => remove_thread causes current_thread to be set to NULL... (that's the recent change mentioned above) => ... which causes problems during lynx_continue, because it calls lynx_resume, which calls regcache_invalidate, which unfortunately assumes that CURRENT_THREAD is not NULL: void regcache_invalidate (void) { /* Only update the threads of the current process. */ SEGV!--> int pid = ptid_get_pid (current_thread->entry.id); find_inferior (&all_threads, regcache_invalidate_one, &pid); } Since the problem at hand is caused by trying to figure out which inferior to reset the regcache for, and since lynx_resume actually had that info, this patch fixes the problem by introducing a new routine called regcache_invalidate_pid, which invalidates the cache of the given pid; and then modifies lynx_resume use that new routine rather than relying on regcache_invalidate to invalidate the regcache of the expected inferior. gdb/gdbserver/ChangeLog: * regcache.h (regcache_invalidate_pid): Add declaration. * regcache.c (regcache_invalidate_pid): New function, extracted from regcache_invalidate. (regcache_invalidate): Reimplement using regcache_invalidate_pid. Add trivial documentation comment. * lynx-low.c: Use regcache_invalidate_pid instead of regcache_invalidate. --- gdb/gdbserver/ChangeLog | 10 ++++++++++ gdb/gdbserver/lynx-low.c | 2 +- gdb/gdbserver/regcache.c | 12 +++++++++++- gdb/gdbserver/regcache.h | 4 ++++ 4 files changed, 26 insertions(+), 2 deletions(-) diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 7e9d695..e265798 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,5 +1,15 @@ 2015-11-23 Joel Brobecker + * regcache.h (regcache_invalidate_pid): Add declaration. + * regcache.c (regcache_invalidate_pid): New function, extracted + from regcache_invalidate. + (regcache_invalidate): Reimplement using regcache_invalidate_pid. + Add trivial documentation comment. + * lynx-low.c: Use regcache_invalidate_pid instead of + regcache_invalidate. + +2015-11-23 Joel Brobecker + * configure.ac: Do not call AC_CHECK_TYPES for Elf32_auxv_t and Elf64_auxv_t if the target is Android. diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c index 0582399..36ab0a3 100644 --- a/gdb/gdbserver/lynx-low.c +++ b/gdb/gdbserver/lynx-low.c @@ -343,7 +343,7 @@ lynx_resume (struct thread_resume *resume_info, size_t n) if (ptid_equal (ptid, minus_one_ptid)) ptid = thread_to_gdb_id (current_thread); - regcache_invalidate (); + regcache_invalidate_pid (ptid_get_pid (ptid)); errno = 0; lynx_ptrace (request, ptid, 1, signal, 0); diff --git a/gdb/gdbserver/regcache.c b/gdb/gdbserver/regcache.c index e11b173..b9311fe 100644 --- a/gdb/gdbserver/regcache.c +++ b/gdb/gdbserver/regcache.c @@ -107,13 +107,23 @@ regcache_invalidate_one (struct inferior_list_entry *entry, return 0; } +/* See regcache.h. */ + +void +regcache_invalidate_pid (int pid) +{ + find_inferior (&all_threads, regcache_invalidate_one, &pid); +} + +/* See regcache.h. */ + void regcache_invalidate (void) { /* Only update the threads of the current process. */ int pid = ptid_get_pid (current_thread->entry.id); - find_inferior (&all_threads, regcache_invalidate_one, &pid); + regcache_invalidate_pid (pid); } #endif diff --git a/gdb/gdbserver/regcache.h b/gdb/gdbserver/regcache.h index d2d9fc7..a0be95e 100644 --- a/gdb/gdbserver/regcache.h +++ b/gdb/gdbserver/regcache.h @@ -74,6 +74,10 @@ void free_register_cache (struct regcache *regcache); void regcache_invalidate_thread (struct thread_info *); +/* Invalidate cached registers for all threads of the given process. */ + +void regcache_invalidate_pid (int pid); + /* Invalidate cached registers for all threads of the current process. */ -- 2.7.4