Avoid crashes on C-g when several threads wait for input

* src/thread.h (m_getcjmp): New member of 'struct thread_state'.
(getcjmp): Define to current thread's 'm_getcjmp'.
* src/thread.c (maybe_reacquire_global_lock): Switch to main
thread, since this is called from a SIGINT handler, which always
runs in the context of the main thread.
* src/lisp.h (sys_jmp_buf, sys_setjmp, sys_longjmp): Move the
definitions before thread.h is included, as thread.h now uses
sys_jmp_buf.
* src/keyboard.c (getcjmp): Remove declaration.
(read_char): Don't call maybe_reacquire_global_lock here.
(handle_interrupt): Call maybe_reacquire_global_lock here, if
invoked from the SIGINT handler, to make sure
quit_throw_to_read_char runs with main thread's Lisp bindings and
uses the main thread's jmp_buf buffer.  (Bug#28630)

1 files changed, 7 insertions, 0 deletions

diff --git a/src/thread.h b/src/thread.h
index 7fce8674f0e..cb2133d72d4 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -158,6 +158,13 @@ struct thread_state
   bool m_waiting_for_input;
 #define waiting_for_input (current_thread->m_waiting_for_input)
 
+  /* For longjmp to where kbd input is being done.  This is per-thread
+     so that if more than one thread calls read_char, they don't
+     clobber each other's getcjmp, which will cause
+     quit_throw_to_read_char crash due to using a wrong stack.  */
+  sys_jmp_buf m_getcjmp;
+#define getcjmp (current_thread->m_getcjmp)
+
   /* The OS identifier for this thread.  */
   sys_thread_t thread_id;