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-- $Id: testes/cstack.lua $
-- See Copyright Notice in file all.lua
local debug = require "debug"
print"testing C-stack overflow detection"
print"If this test crashes, see its file ('cstack.lua')"
-- Segmentation faults in these tests probably result from a C-stack
-- overflow. To avoid these errors, you can use the function
-- 'debug.setcstacklimit' to set a smaller limit for the use of
-- C stack by Lua. After finding a reliable limit, you might want
-- to recompile Lua with this limit as the value for
-- the constant 'LUAI_MAXCCALLS', which defines the default limit.
-- (The default limit is printed by this test.)
-- Alternatively, you can ensure a larger stack for the program.
-- For Linux, a limit up to 30_000 seems Ok. Windows cannot go much
-- higher than 2_000.
-- get and print original limit
local origlimit <const> = debug.setcstacklimit(400)
print("default stack limit: " .. origlimit)
-- Do the tests using the original limit. Or else you may want to change
-- 'currentlimit' to lower values to avoid a seg. fault or to higher
-- values to check whether they are reliable.
local currentlimit <const> = origlimit
print("current stack limit: " .. currentlimit)
local function checkerror (msg, f, ...)
local s, err = pcall(f, ...)
assert(not s and string.find(err, msg))
-- auxiliary function to keep 'count' on the screen even if the program
-- crashes.
local count
local back = string.rep("\b", 8)
local function progress ()
count = count + 1
local n = string.format("%-8d", count)
io.stderr:write(back, n) -- erase previous value and write new one
do print("testing simple recursion:")
count = 0
local function foo ()
foo() -- do recursive calls until a stack error (or crash)
checkerror("stack overflow", foo)
print("\tfinal count: ", count)
do print("testing stack overflow in message handling")
count = 0
local function loop (x, y, z)
return 1 + loop(x, y, z)
local res, msg = xpcall(loop, loop)
assert(msg == "error in error handling")
print("\tfinal count: ", count)
-- bug since 2.5 (C-stack overflow in recursion inside pattern matching)
do print("testing recursion inside pattern matching")
local function f (size)
local s = string.rep("a", size)
local p = string.rep(".?", size)
return string.match(s, p)
local m = f(80)
assert(#m == 80)
checkerror("too complex", f, 200000)
do print("testing stack-overflow in recursive 'gsub'")
count = 0
local function foo ()
string.gsub("a", ".", foo)
checkerror("stack overflow", foo)
print("\tfinal count: ", count)
print("testing stack-overflow in recursive 'gsub' with metatables")
count = 0
local t = setmetatable({}, {__index = foo})
foo = function ()
count = count + 1
string.gsub("a", ".", t)
checkerror("stack overflow", foo)
print("\tfinal count: ", count)
do print("testing changes in C-stack limit")
-- Just an alternative limit, different from the current one
-- (smaller to avoid stack overflows)
local alterlimit <const> = currentlimit * 8 // 10
assert(not debug.setcstacklimit(0)) -- limit too small
assert(not debug.setcstacklimit(50000)) -- limit too large
local co = coroutine.wrap (function ()
return debug.setcstacklimit(alterlimit)
assert(not co()) -- cannot change C stack inside coroutine
local n
local function foo () n = n + 1; foo () end
local function check ()
n = 0
return n
-- set limit to 'alterlimit'
assert(debug.setcstacklimit(alterlimit) == currentlimit)
local limalter <const> = check()
-- set a very low limit (given that there are already several active
-- calls to arrive here)
local lowlimit <const> = 38
assert(debug.setcstacklimit(lowlimit) == alterlimit)
-- usable limit is much lower, due to active calls
local actuallow = check()
assert(actuallow < lowlimit - 30)
-- now, add 'lowlimit' extra slots, which should all be available
assert(debug.setcstacklimit(lowlimit + lowlimit) == lowlimit)
local lim2 <const> = check()
assert(lim2 == actuallow + lowlimit)
-- 'setcstacklimit' works inside protected calls. (The new stack
-- limit is kept when 'pcall' returns.)
assert(pcall(function ()
assert(debug.setcstacklimit(alterlimit) == lowlimit * 2)
assert(check() <= limalter)
assert(check() == limalter)
-- restore original limit
assert(debug.setcstacklimit(origlimit) == alterlimit)