From 9dee1c884eb50ba282eb9dd2495c5269add25963 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Fri, 14 Jul 2017 04:54:05 -0700 Subject: [PATCH] Improve stack-overflow heuristic on GNU/Linux Problem reported by Steve Kemp (Bug#27585). * src/eval.c (near_C_stack_top): Remove. All uses replaced by current_thread->stack_top. (record_in_backtrace): Set current_thread->stack_top. This is for when the Lisp interpreter calls itself. * src/lread.c (read1): Set current_thread->stack_top. This is for recursive s-expression reads. * src/print.c (print_object): Set current_thread->stack_top. This is for recursive s-expression printing. * src/thread.c (mark_one_thread): Get stack top first. * src/thread.h (struct thread_state.stack_top): Now void *, not char *. --- src/eval.c | 9 +-------- src/lisp.h | 1 - src/lread.c | 1 + src/print.c | 2 +- src/sysdep.c | 2 +- src/thread.c | 10 ++++++---- src/thread.h | 10 ++++++++-- 7 files changed, 18 insertions(+), 17 deletions(-) diff --git a/src/eval.c b/src/eval.c index 8f293c9..e590038 100644 --- a/src/eval.c +++ b/src/eval.c @@ -213,13 +213,6 @@ backtrace_next (union specbinding *pdl) return pdl; } -/* Return a pointer to somewhere near the top of the C stack. */ -void * -near_C_stack_top (void) -{ - return backtrace_args (backtrace_top ()); -} - void init_eval_once (void) { @@ -2090,7 +2083,7 @@ record_in_backtrace (Lisp_Object function, Lisp_Object *args, ptrdiff_t nargs) specpdl_ptr->bt.kind = SPECPDL_BACKTRACE; specpdl_ptr->bt.debug_on_exit = false; specpdl_ptr->bt.function = function; - specpdl_ptr->bt.args = args; + current_thread->stack_top = specpdl_ptr->bt.args = args; specpdl_ptr->bt.nargs = nargs; grow_specpdl (); diff --git a/src/lisp.h b/src/lisp.h index f5cb6c7..1e8ef7a 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -3874,7 +3874,6 @@ extern Lisp_Object vformat_string (const char *, va_list) ATTRIBUTE_FORMAT_PRINTF (1, 0); extern void un_autoload (Lisp_Object); extern Lisp_Object call_debugger (Lisp_Object arg); -extern void *near_C_stack_top (void); extern void init_eval_once (void); extern Lisp_Object safe_call (ptrdiff_t, Lisp_Object, ...); extern Lisp_Object safe_call1 (Lisp_Object, Lisp_Object); diff --git a/src/lread.c b/src/lread.c index fe5de38..901e40b 100644 --- a/src/lread.c +++ b/src/lread.c @@ -2676,6 +2676,7 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list) bool uninterned_symbol = false; bool multibyte; char stackbuf[MAX_ALLOCA]; + current_thread->stack_top = stackbuf; *pch = 0; diff --git a/src/print.c b/src/print.c index b6ea3ff..12edf01 100644 --- a/src/print.c +++ b/src/print.c @@ -1748,7 +1748,7 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag) char buf[max (sizeof "from..to..in " + 2 * INT_STRLEN_BOUND (EMACS_INT), max (sizeof " . #" + INT_STRLEN_BOUND (printmax_t), 40))]; - + current_thread->stack_top = buf; maybe_quit (); /* Detect circularities and truncate them. */ diff --git a/src/sysdep.c b/src/sysdep.c index b522367..db99f53 100644 --- a/src/sysdep.c +++ b/src/sysdep.c @@ -1772,7 +1772,7 @@ stack_overflow (siginfo_t *siginfo) /* The known top and bottom of the stack. The actual stack may extend a bit beyond these boundaries. */ char *bot = stack_bottom; - char *top = near_C_stack_top (); + char *top = current_thread->stack_top; /* Log base 2 of the stack heuristic ratio. This ratio is the size of the known stack divided by the size of the guard area past the diff --git a/src/thread.c b/src/thread.c index e378797..1f7ced3 100644 --- a/src/thread.c +++ b/src/thread.c @@ -595,14 +595,15 @@ thread_select (select_func *func, int max_fds, fd_set *rfds, static void mark_one_thread (struct thread_state *thread) { - struct handler *handler; - Lisp_Object tem; + /* Get the stack top now, in case mark_specpdl changes it. */ + void *stack_top = thread->stack_top; mark_specpdl (thread->m_specpdl, thread->m_specpdl_ptr); - mark_stack (thread->m_stack_bottom, thread->stack_top); + mark_stack (thread->m_stack_bottom, stack_top); - for (handler = thread->m_handlerlist; handler; handler = handler->next) + for (struct handler *handler = thread->m_handlerlist; + handler; handler = handler->next) { mark_object (handler->tag_or_ch); mark_object (handler->val); @@ -610,6 +611,7 @@ mark_one_thread (struct thread_state *thread) if (thread->m_current_buffer) { + Lisp_Object tem; XSETBUFFER (tem, thread->m_current_buffer); mark_object (tem); } diff --git a/src/thread.h b/src/thread.h index 9e94de5..52b16f1 100644 --- a/src/thread.h +++ b/src/thread.h @@ -62,8 +62,14 @@ struct thread_state char *m_stack_bottom; #define stack_bottom (current_thread->m_stack_bottom) - /* An address near the top of the stack. */ - char *stack_top; + /* The address of an object near the C stack top, used to determine + which words need to be scanned by the garbage collector. This is + also used to detect heuristically whether segmentation violation + address indicates stack overflow, as opposed to some internal + error in Emacs. If the C function F calls G which calls H which + calls ... F, then at least one of the functions in the chain + should set this to the address of a local variable. */ + void *stack_top; struct catchtag *m_catchlist; #define catchlist (current_thread->m_catchlist) -- 2.7.4