luau/VM/src/ldo.cpp

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// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
// This code is based on Lua 5.x implementation licensed under MIT License; see lua_LICENSE.txt for details
#include "ldo.h"
#include "lstring.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lvm.h"
#if LUA_USE_LONGJMP
#include <setjmp.h>
#include <stdlib.h>
#else
#include <stdexcept>
#endif
#include <string.h>
LUAU_FASTFLAGVARIABLE(LuauCcallRestoreFix, false)
LUAU_FASTFLAG(LuauCoroutineClose)
LUAU_FASTFLAGVARIABLE(LuauActivateBeforeExec, true)
/*
** {======================================================
** Error-recovery functions
** =======================================================
*/
#if LUA_USE_LONGJMP
struct lua_jmpbuf
{
lua_jmpbuf* volatile prev;
volatile int status;
jmp_buf buf;
};
int luaD_rawrunprotected(lua_State* L, Pfunc f, void* ud)
{
lua_jmpbuf jb;
jb.prev = L->global->errorjmp;
jb.status = 0;
L->global->errorjmp = &jb;
if (setjmp(jb.buf) == 0)
f(L, ud);
L->global->errorjmp = jb.prev;
return jb.status;
}
l_noret luaD_throw(lua_State* L, int errcode)
{
if (lua_jmpbuf* jb = L->global->errorjmp)
{
jb->status = errcode;
longjmp(jb->buf, 1);
}
if (L->global->cb.panic)
L->global->cb.panic(L, errcode);
abort();
}
#else
class lua_exception : public std::exception
{
public:
lua_exception(lua_State* L, int status)
: L(L)
, status(status)
{
}
const char* what() const throw() override
{
// LUA_ERRRUN/LUA_ERRSYNTAX pass an object on the stack which is intended to describe the error.
if (status == LUA_ERRRUN || status == LUA_ERRSYNTAX)
{
// Conversion to a string could still fail. For example if a user passes a non-string/non-number argument to `error()`.
if (const char* str = lua_tostring(L, -1))
{
return str;
}
}
switch (status)
{
case LUA_ERRRUN:
return "lua_exception: LUA_ERRRUN (no string/number provided as description)";
case LUA_ERRSYNTAX:
return "lua_exception: LUA_ERRSYNTAX (no string/number provided as description)";
case LUA_ERRMEM:
return "lua_exception: " LUA_MEMERRMSG;
case LUA_ERRERR:
return "lua_exception: " LUA_ERRERRMSG;
default:
return "lua_exception: unexpected exception status";
}
}
int getStatus() const
{
return status;
}
private:
lua_State* L;
int status;
};
int luaD_rawrunprotected(lua_State* L, Pfunc f, void* ud)
{
int status = 0;
try
{
f(L, ud);
return 0;
}
catch (lua_exception& e)
{
// lua_exception means that luaD_throw was called and an exception object is on stack if status is ERRRUN
status = e.getStatus();
}
catch (std::exception& e)
{
// Luau will never throw this, but this can catch exceptions that escape from C++ implementations of external functions
try
{
// there's no exception object on stack; let's push the error on stack so that error handling below can proceed
luaG_pusherror(L, e.what());
status = LUA_ERRRUN;
}
catch (std::exception&)
{
// out of memory while allocating error string
status = LUA_ERRMEM;
}
}
return status;
}
l_noret luaD_throw(lua_State* L, int errcode)
{
throw lua_exception(L, errcode);
}
#endif
/* }====================================================== */
static void correctstack(lua_State* L, TValue* oldstack)
{
CallInfo* ci;
GCObject* up;
L->top = (L->top - oldstack) + L->stack;
for (up = L->openupval; up != NULL; up = up->gch.next)
gco2uv(up)->v = (gco2uv(up)->v - oldstack) + L->stack;
for (ci = L->base_ci; ci <= L->ci; ci++)
{
ci->top = (ci->top - oldstack) + L->stack;
ci->base = (ci->base - oldstack) + L->stack;
ci->func = (ci->func - oldstack) + L->stack;
}
L->base = (L->base - oldstack) + L->stack;
}
void luaD_reallocstack(lua_State* L, int newsize)
{
TValue* oldstack = L->stack;
int realsize = newsize + 1 + EXTRA_STACK;
LUAU_ASSERT(L->stack_last - L->stack == L->stacksize - EXTRA_STACK - 1);
luaM_reallocarray(L, L->stack, L->stacksize, realsize, TValue, L->memcat);
for (int i = L->stacksize; i < realsize; i++)
setnilvalue(L->stack + i); /* erase new segment */
L->stacksize = realsize;
L->stack_last = L->stack + newsize;
correctstack(L, oldstack);
}
void luaD_reallocCI(lua_State* L, int newsize)
{
CallInfo* oldci = L->base_ci;
luaM_reallocarray(L, L->base_ci, L->size_ci, newsize, CallInfo, L->memcat);
L->size_ci = newsize;
L->ci = (L->ci - oldci) + L->base_ci;
L->end_ci = L->base_ci + L->size_ci - 1;
}
void luaD_growstack(lua_State* L, int n)
{
if (n <= L->stacksize) /* double size is enough? */
luaD_reallocstack(L, 2 * L->stacksize);
else
luaD_reallocstack(L, L->stacksize + n);
}
CallInfo* luaD_growCI(lua_State* L)
{
if (L->size_ci > LUAI_MAXCALLS) /* overflow while handling overflow? */
luaD_throw(L, LUA_ERRERR);
else
{
luaD_reallocCI(L, 2 * L->size_ci);
if (L->size_ci > LUAI_MAXCALLS)
luaG_runerror(L, "stack overflow");
}
return ++L->ci;
}
/*
** Call a function (C or Lua). The function to be called is at *func.
** The arguments are on the stack, right after the function.
** When returns, all the results are on the stack, starting at the original
** function position.
*/
void luaD_call(lua_State* L, StkId func, int nResults)
{
if (++L->nCcalls >= LUAI_MAXCCALLS)
{
if (L->nCcalls == LUAI_MAXCCALLS)
luaG_runerror(L, "C stack overflow");
else if (L->nCcalls >= (LUAI_MAXCCALLS + (LUAI_MAXCCALLS >> 3)))
luaD_throw(L, LUA_ERRERR); /* error while handing stack error */
}
if (luau_precall(L, func, nResults) == PCRLUA)
{ /* is a Lua function? */
L->ci->flags |= LUA_CALLINFO_RETURN; /* luau_execute will stop after returning from the stack frame */
if (FFlag::LuauActivateBeforeExec)
{
int oldactive = luaC_threadactive(L);
l_setbit(L->stackstate, THREAD_ACTIVEBIT);
luaC_checkthreadsleep(L);
luau_execute(L); /* call it */
if (!oldactive)
resetbit(L->stackstate, THREAD_ACTIVEBIT);
}
else
{
luau_execute(L); /* call it */
}
}
L->nCcalls--;
luaC_checkGC(L);
}
static void seterrorobj(lua_State* L, int errcode, StkId oldtop)
{
switch (errcode)
{
case LUA_ERRMEM:
{
setsvalue2s(L, oldtop, luaS_newliteral(L, LUA_MEMERRMSG)); /* can not fail because string is pinned in luaopen */
break;
}
case LUA_ERRERR:
{
setsvalue2s(L, oldtop, luaS_newliteral(L, LUA_ERRERRMSG)); /* can not fail because string is pinned in luaopen */
break;
}
case LUA_ERRSYNTAX:
case LUA_ERRRUN:
{
setobjs2s(L, oldtop, L->top - 1); /* error message on current top */
break;
}
}
L->top = oldtop + 1;
}
static void resume_continue(lua_State* L)
{
// unroll Lua/C combined stack, processing continuations
while (L->status == 0 && L->ci > L->base_ci)
{
LUAU_ASSERT(L->baseCcalls == L->nCcalls);
Closure* cl = curr_func(L);
if (cl->isC)
{
LUAU_ASSERT(cl->c.cont);
// C continuation; we expect this to be followed by Lua continuations
int n = cl->c.cont(L, 0);
// Continuation can break again
if (L->status == LUA_BREAK)
break;
luau_poscall(L, L->top - n);
}
else
{
// Lua continuation; it terminates at the end of the stack or at another C continuation
luau_execute(L);
}
}
}
static void resume(lua_State* L, void* ud)
{
StkId firstArg = cast_to(StkId, ud);
if (L->status == 0)
{
// start coroutine
LUAU_ASSERT(L->ci == L->base_ci && firstArg >= L->base);
if (FFlag::LuauCoroutineClose && firstArg == L->base)
luaG_runerror(L, "cannot resume dead coroutine");
if (luau_precall(L, firstArg - 1, LUA_MULTRET) != PCRLUA)
return;
L->ci->flags |= LUA_CALLINFO_RETURN;
}
else
{
// resume from previous yield or break
LUAU_ASSERT(L->status == LUA_YIELD || L->status == LUA_BREAK);
L->status = 0;
Closure* cl = curr_func(L);
if (cl->isC)
{
// if the top stack frame is a C call continuation, resume_continue will handle that case
if (!cl->c.cont)
{
// finish interrupted execution of `OP_CALL'
luau_poscall(L, firstArg);
}
}
else
{
// yielded inside a hook: just continue its execution
L->base = L->ci->base;
}
}
// run continuations from the stack; typically resumes Lua code and pcalls
resume_continue(L);
}
static CallInfo* resume_findhandler(lua_State* L)
{
CallInfo* ci = L->ci;
while (ci > L->base_ci)
{
if (ci->flags & LUA_CALLINFO_HANDLE)
return ci;
ci--;
}
return NULL;
}
static void resume_handle(lua_State* L, void* ud)
{
CallInfo* ci = (CallInfo*)ud;
Closure* cl = ci_func(ci);
LUAU_ASSERT(ci->flags & LUA_CALLINFO_HANDLE);
LUAU_ASSERT(cl->isC && cl->c.cont);
LUAU_ASSERT(L->status != 0);
// restore nCcalls back to base since this might not have happened during error handling
L->nCcalls = L->baseCcalls;
// make sure we don't run the handler the second time
ci->flags &= ~LUA_CALLINFO_HANDLE;
// restore thread status to 0 since we're handling the error
int status = L->status;
L->status = 0;
// push error object to stack top if it's not already there
if (status != LUA_ERRRUN)
seterrorobj(L, status, L->top);
// adjust the stack frame for ci to prepare for cont call
L->base = ci->base;
ci->top = L->top;
// save ci pointer - it will be invalidated by cont call!
ptrdiff_t old_ci = saveci(L, ci);
// handle the error in continuation; note that this executes on top of original stack!
int n = cl->c.cont(L, status);
// restore the stack frame to the frame with continuation
L->ci = restoreci(L, old_ci);
// close eventual pending closures; this means it's now safe to restore stack
luaF_close(L, L->base);
// finish cont call and restore stack to previous ci top
luau_poscall(L, L->top - n);
// run remaining continuations from the stack; typically resumes pcalls
resume_continue(L);
}
static int resume_error(lua_State* L, const char* msg)
{
L->top = L->ci->base;
setsvalue2s(L, L->top, luaS_new(L, msg));
incr_top(L);
return LUA_ERRRUN;
}
static void resume_finish(lua_State* L, int status)
{
L->nCcalls = L->baseCcalls;
resetbit(L->stackstate, THREAD_ACTIVEBIT);
if (status != 0)
{ /* error? */
L->status = cast_byte(status); /* mark thread as `dead' */
seterrorobj(L, status, L->top);
L->ci->top = L->top;
}
else if (L->status == 0)
{
expandstacklimit(L, L->top);
}
}
int lua_resume(lua_State* L, lua_State* from, int nargs)
{
int status;
if (L->status != LUA_YIELD && L->status != LUA_BREAK && (L->status != 0 || L->ci != L->base_ci))
return resume_error(L, "cannot resume non-suspended coroutine");
L->nCcalls = from ? from->nCcalls : 0;
if (L->nCcalls >= LUAI_MAXCCALLS)
return resume_error(L, "C stack overflow");
L->baseCcalls = ++L->nCcalls;
l_setbit(L->stackstate, THREAD_ACTIVEBIT);
luaC_checkthreadsleep(L);
status = luaD_rawrunprotected(L, resume, L->top - nargs);
CallInfo* ch = NULL;
while (status != 0 && (ch = resume_findhandler(L)) != NULL)
{
L->status = cast_byte(status);
status = luaD_rawrunprotected(L, resume_handle, ch);
}
resume_finish(L, status);
--L->nCcalls;
return L->status;
}
int lua_resumeerror(lua_State* L, lua_State* from)
{
int status;
if (L->status != LUA_YIELD && L->status != LUA_BREAK && (L->status != 0 || L->ci != L->base_ci))
return resume_error(L, "cannot resume non-suspended coroutine");
L->nCcalls = from ? from->nCcalls : 0;
if (L->nCcalls >= LUAI_MAXCCALLS)
return resume_error(L, "C stack overflow");
L->baseCcalls = ++L->nCcalls;
l_setbit(L->stackstate, THREAD_ACTIVEBIT);
luaC_checkthreadsleep(L);
status = LUA_ERRRUN;
CallInfo* ch = NULL;
while (status != 0 && (ch = resume_findhandler(L)) != NULL)
{
L->status = cast_byte(status);
status = luaD_rawrunprotected(L, resume_handle, ch);
}
resume_finish(L, status);
--L->nCcalls;
return L->status;
}
int lua_yield(lua_State* L, int nresults)
{
if (L->nCcalls > L->baseCcalls)
luaG_runerror(L, "attempt to yield across metamethod/C-call boundary");
L->base = L->top - nresults; /* protect stack slots below */
L->status = LUA_YIELD;
return -1;
}
int lua_break(lua_State* L)
{
if (L->nCcalls > L->baseCcalls)
luaG_runerror(L, "attempt to break across metamethod/C-call boundary");
L->status = LUA_BREAK;
return -1;
}
int lua_isyieldable(lua_State* L)
{
return (L->nCcalls <= L->baseCcalls);
}
static void callerrfunc(lua_State* L, void* ud)
{
StkId errfunc = cast_to(StkId, ud);
setobjs2s(L, L->top, L->top - 1);
setobjs2s(L, L->top - 1, errfunc);
incr_top(L);
luaD_call(L, L->top - 2, 1);
}
static void restore_stack_limit(lua_State* L)
{
LUAU_ASSERT(L->stack_last - L->stack == L->stacksize - EXTRA_STACK - 1);
if (L->size_ci > LUAI_MAXCALLS)
{ /* there was an overflow? */
int inuse = cast_int(L->ci - L->base_ci);
if (inuse + 1 < LUAI_MAXCALLS) /* can `undo' overflow? */
luaD_reallocCI(L, LUAI_MAXCALLS);
}
}
int luaD_pcall(lua_State* L, Pfunc func, void* u, ptrdiff_t old_top, ptrdiff_t ef)
{
unsigned short oldnCcalls = L->nCcalls;
ptrdiff_t old_ci = saveci(L, L->ci);
int oldactive = luaC_threadactive(L);
int status = luaD_rawrunprotected(L, func, u);
if (status != 0)
{
// call user-defined error function (used in xpcall)
if (ef)
{
// if errfunc fails, we fail with "error in error handling"
if (luaD_rawrunprotected(L, callerrfunc, restorestack(L, ef)) != 0)
status = LUA_ERRERR;
}
if (FFlag::LuauActivateBeforeExec)
{
// since the call failed with an error, we might have to reset the 'active' thread state
if (!oldactive)
resetbit(L->stackstate, THREAD_ACTIVEBIT);
}
if (FFlag::LuauCcallRestoreFix)
{
// Restore nCcalls before calling the debugprotectederror callback which may rely on the proper value to have been restored.
L->nCcalls = oldnCcalls;
}
// an error occurred, check if we have a protected error callback
if (L->global->cb.debugprotectederror)
{
L->global->cb.debugprotectederror(L);
// debug hook is only allowed to break
if (L->status == LUA_BREAK)
return 0;
}
StkId oldtop = restorestack(L, old_top);
luaF_close(L, oldtop); /* close eventual pending closures */
seterrorobj(L, status, oldtop);
if (!FFlag::LuauCcallRestoreFix)
{
L->nCcalls = oldnCcalls;
}
L->ci = restoreci(L, old_ci);
L->base = L->ci->base;
restore_stack_limit(L);
}
return status;
}