From 17dbaa8639505c9ad1a9946591f5960123fbd741 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Fri, 22 May 2020 11:40:34 -0300
Subject: [PATCH] Improvements in the handling of signals

Added 'volatile' to 'l_signalT' variables plus some minor changes.
---
 ldebug.c | 20 +++++++++++---------
 ldo.c    | 10 +++++-----
 lstate.c |  9 +++++----
 lstate.h |  4 ++--
 lua.c    |  3 ++-
 5 files changed, 25 insertions(+), 21 deletions(-)

diff --git a/ldebug.c b/ldebug.c
index eaac16f7..afdc2b74 100644
--- a/ldebug.c
+++ b/ldebug.c
@@ -107,13 +107,15 @@ static int getcurrentline (CallInfo *ci) {
 
 
 /*
-** This function can be called asynchronously (e.g. during a signal),
-** under "reasonable" assumptions. A new 'ci' is completely linked
-** in the list before it becomes part of the "active" list, and
-** we assume that pointers are atomic (see comment in next function).
-** (If we traverse one more item, there is no problem. If we traverse
-** one less item, the worst that can happen is that the signal will
-** not interrupt the script.)
+** Set 'trap' for all active Lua frames.
+** This function can be called during a signal, under "reasonable"
+** assumptions. A new 'ci' is completely linked in the list before it
+** becomes part of the "active" list, and we assume that pointers are
+** atomic; see comment in next function.
+** (A compiler doing interprocedural optimizations could, theoretically,
+** reorder memory writes in such a way that the list could be
+** temporarily broken while inserting a new element. We simply assume it
+** has no good reasons to do that.)
 */
 static void settraps (CallInfo *ci) {
   for (; ci != NULL; ci = ci->previous)
@@ -123,8 +125,8 @@ static void settraps (CallInfo *ci) {
 
 
 /*
-** This function can be called asynchronously (e.g. during a signal),
-** under "reasonable" assumptions.
+** This function can be called during a signal, under "reasonable"
+** assumptions.
 ** Fields 'oldpc', 'basehookcount', and 'hookcount' (set by
 ** 'resethookcount') are for debug only, and it is no problem if they
 ** get arbitrary values (causes at most one wrong hook call). 'hookmask'
diff --git a/ldo.c b/ldo.c
index 64fe2915..c563b1d9 100644
--- a/ldo.c
+++ b/ldo.c
@@ -422,7 +422,7 @@ void luaD_poscall (lua_State *L, CallInfo *ci, int nres) {
 
 
 
-#define next_ci(L)  (L->ci = (L->ci->next ? L->ci->next : luaE_extendCI(L)))
+#define next_ci(L)  (L->ci->next ? L->ci->next : luaE_extendCI(L))
 
 
 /*
@@ -466,13 +466,13 @@ void luaD_call (lua_State *L, StkId func, int nresults) {
       f = fvalue(s2v(func));
      Cfunc: {
       int n;  /* number of returns */
-      CallInfo *ci;
+      CallInfo *ci = next_ci(L);
       checkstackp(L, LUA_MINSTACK, func);  /* ensure minimum stack size */
-      ci = next_ci(L);
       ci->nresults = nresults;
       ci->callstatus = CIST_C;
       ci->top = L->top + LUA_MINSTACK;
       ci->func = func;
+      L->ci = ci;
       lua_assert(ci->top <= L->stack_last);
       if (L->hookmask & LUA_MASKCALL) {
         int narg = cast_int(L->top - func) - 1;
@@ -486,18 +486,18 @@ void luaD_call (lua_State *L, StkId func, int nresults) {
       break;
     }
     case LUA_VLCL: {  /* Lua function */
-      CallInfo *ci;
+      CallInfo *ci = next_ci(L);
       Proto *p = clLvalue(s2v(func))->p;
       int narg = cast_int(L->top - func) - 1;  /* number of real arguments */
       int nfixparams = p->numparams;
       int fsize = p->maxstacksize;  /* frame size */
       checkstackp(L, fsize, func);
-      ci = next_ci(L);
       ci->nresults = nresults;
       ci->u.l.savedpc = p->code;  /* starting point */
       ci->callstatus = 0;
       ci->top = func + 1 + fsize;
       ci->func = func;
+      L->ci = ci;
       for (; narg < nfixparams; narg++)
         setnilvalue(s2v(L->top++));  /* complete missing arguments */
       lua_assert(ci->top <= L->stack_last);
diff --git a/lstate.c b/lstate.c
index 8fba70d7..42a48436 100644
--- a/lstate.c
+++ b/lstate.c
@@ -190,14 +190,15 @@ void luaE_freeCI (lua_State *L) {
 */
 void luaE_shrinkCI (lua_State *L) {
   CallInfo *ci = L->ci;
+  CallInfo *next;
   CallInfo *next2;  /* next's next */
   L->nCcalls += L->nci;  /* add removed elements back to 'nCcalls' */
   /* while there are two nexts */
-  while (ci->next != NULL && (next2 = ci->next->next) != NULL) {
-    luaM_free(L, ci->next);  /* free next */
-    L->nci--;
-    ci->next = next2;  /* remove 'next' from the list */
+  while ((next = ci->next) != NULL && (next2 = next->next) != NULL) {
+    ci->next = next2;  /* remove next from the list */
     next2->previous = ci;
+    luaM_free(L, next);  /* free next */
+    L->nci--;
     ci = next2;  /* keep next's next */
   }
   L->nCcalls -= L->nci;  /* adjust result */
diff --git a/lstate.h b/lstate.h
index df9148eb..2e8bd6c4 100644
--- a/lstate.h
+++ b/lstate.h
@@ -173,7 +173,7 @@ typedef struct CallInfo {
   union {
     struct {  /* only for Lua functions */
       const Instruction *savedpc;
-      l_signalT trap;
+      volatile l_signalT trap;
       int nextraargs;  /* # of extra arguments in vararg functions */
     } l;
     struct {  /* only for C functions */
@@ -300,7 +300,7 @@ struct lua_State {
   int stacksize;
   int basehookcount;
   int hookcount;
-  l_signalT hookmask;
+  volatile l_signalT hookmask;
 };
 
 
diff --git a/lua.c b/lua.c
index 18f53c30..454ce12f 100644
--- a/lua.c
+++ b/lua.c
@@ -54,8 +54,9 @@ static void lstop (lua_State *L, lua_Debug *ar) {
 ** interpreter.
 */
 static void laction (int i) {
+  int flag = LUA_MASKCALL | LUA_MASKRET | LUA_MASKLINE | LUA_MASKCOUNT;
   signal(i, SIG_DFL); /* if another SIGINT happens, terminate process */
-  lua_sethook(globalL, lstop, LUA_MASKCALL | LUA_MASKRET | LUA_MASKCOUNT, 1);
+  lua_sethook(globalL, lstop, flag, 1);
 }