On 8 Oct 2021, at 11:39, Sergey Kaplun <skaplun@tarantool.org> wrote:

Hi, Sergos!

Thanks for the review!

On 07.10.21, sergos wrote:

Hi!
Thanks for the patch! See my 2 comments below.

Sergos

On 5 Oct 2021, at 13:28, Sergey Kaplun <skaplun@tarantool.org> wrote:

From: Mike Pall <mike>

Reported by Changochen.

(cherry picked from 53f82e6e2e858a0a62fd1a2ff47e9866693382e6)

Additional stack traversal is needed to find an error function set for

  ^^^                          ^^^
Additional to what?            

I mean additional to stack traversal during error raising to find
protected frame, but it is confusing, so I rephrase it as you suggested.

handling runtime errors. cframe unwinding is missed for a C protected
frame during this stack traversal.

I would rephrase - 
A cframe unwinding is miseed for a C protected frame during a serach for 
an error function to handle a runtime error. 

It leads to undefined behaviour or
crash, when raising a runtime error on stack with the CP frame before an
error function handler (for example, an error in __gc handler).

This patch adds missing unwinding for CP frame.

Sergey Kaplun:
* added the description and the test for the problem
---

The new commit message is the following:

| Fix frame traversal for __gc handler frames.
|
| Reported by Changochen.
|
| (cherry picked from 53f82e6e2e858a0a62fd1a2ff47e9866693382e6)
|
| A cframe unwinding is missed for a C protected frame during a search for
| an error function to handle a runtime error. It leads to undefined
| behaviour or crash, when raising a runtime error on stack with the CP
| frame before an error function handler (for example, an error in __gc
| handler).
|
| This patch adds missing unwinding for CP frame.
|
| Sergey Kaplun:
| * added the description and the test for the problem

Branch is force-pushed.

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-601-fix-gc-finderrfunc
Tarantool branch: https://github.com/tarantool/tarantool/tree/skaplun/gh-noticket-fix-gc-finderrfunc
LuaJIT issue: https://github.com/LuaJIT/LuaJIT/issues/601

src/lj_err.c                                  |  1 +
.../lj-601-fix-gc-finderrfunc.test.lua        | 25 +++++++++++++++++++
2 files changed, 26 insertions(+)
create mode 100644 test/tarantool-tests/lj-601-fix-gc-finderrfunc.test.lua

diff --git a/src/lj_err.c b/src/lj_err.c
index b6be357e..b520b3d3 100644
--- a/src/lj_err.c
+++ b/src/lj_err.c
@@ -585,6 +585,7 @@ static ptrdiff_t finderrfunc(lua_State *L)
     if (cframe_canyield(cf)) return 0;
     if (cframe_errfunc(cf) >= 0)
return cframe_errfunc(cf);
+      cf = cframe_prev(cf);
     frame = frame_prevd(frame);
     break;
   case FRAME_PCALL:
diff --git a/test/tarantool-tests/lj-601-fix-gc-finderrfunc.test.lua b/test/tarantool-tests/lj-601-fix-gc-finderrfunc.test.lua
new file mode 100644
index 00000000..d8d79100
--- /dev/null
+++ b/test/tarantool-tests/lj-601-fix-gc-finderrfunc.test.lua

Unfortunately the test passes on the ’tarantool’ branch 

s-ostanevich:luajit s.ostanevich$ git checkout tarantool
Switched to branch 'tarantool'
s-ostanevich:luajit s.ostanevich$ git clean -xdff
[…]
s-ostanevich:luajit s.ostanevich$ cmake .
[…]
s-ostanevich:luajit s.ostanevich$ make
[…]
[100%] Built target libluajit_shared
[100%] Built target libluajit
[100%] Built target luajit
s-ostanevich:luajit s.ostanevich$ git checkout   skaplun/lj-601-fix-gc-finderrfunc
s-ostanevich:luajit s.ostanevich$ cd test/tarantool-tests
s-ostanevich:tarantool-tests s.ostanevich$ ../../src/luajit lj-601-fix-gc-finderrfunc.test.lua 
TAP version 13
1..1
ok - successfully collectgarbage with error

Wild guess: it doesn't fail on Mac due to GC64 ;).
See CI [1] to check my hypothesis.

@@ -0,0 +1,25 @@
+local tap = require('tap')
+
+local test = tap.test('lj-601-fix-gc-finderrfunc')
+test:plan(1)
+
+-- Test file to demonstrate LuaJIT incorrect behaviour, when
+-- throwing error in __gc finalizer.
+-- See also, https://github.com/LuaJIT/LuaJIT/issues/601.
+
+collectgarbage()
+
+local a = newproxy(true)
+getmetatable(a).__gc = function()
+  -- Function to raise error via `lj_err_run()` inside __gc.
+  local _ = load(function() collectgarbage()() end)
+end
+
+-- XXX: Generate a small bunch of proxies. Need several to call
+-- `collectgarbage()` on another proxy inside __gc. N cycles is
+-- empirical number.
+for _ = 1, 4 do newproxy(a) end
+collectgarbage('collect')
+
+test:ok(true, 'successfully collectgarbage with error')
+os.exit(test:check() and 0 or 1)
-- 
2.31.0

[1]: https://github.com/tarantool/tarantool/tree/skaplun/gh-noticket-fix-gc-finderrfunc-no-fix

-- 
Best regards,
Sergey Kaplun