[Tarantool-patches] [PATCH luajit] FFI: Always fall back to metamethods for cdata length/concat.

[Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

From: Mike Pall <mike>

Thanks to Egor Skriptunoff.

(cherry picked from commit cc4bbec483d3f3250b519ccb7cc22f1a8e6fe6f0)

When user tries to concatenate 2 cdata objects without declared
metamethod, the assertion is raised in `carith_int64()`, due to
concatenation operation is not specified and default (assert) branch is
taken.

This patch forcifies usage of metamethod for concatenation on cdata
objects. Also, as far as the behaviour for length operation is the same,
the `lj_carith_len()` routine is removed, its call is replaced with
`ffi_arith()`.

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

Part of tarantool/tarantool#7230
---

Issue: https://github.com/tarantool/tarantool/issues/7230
Branch: https://github.com/tarantool/luajit/tree/skaplun/gh-noticket-cdata-ll-concat-full-ci
PR: https://github.com/tarantool/tarantool/pull/7598
ML: https://www.freelists.org/post/luajit/cdata-concatenation

 src/lj_carith.c                                |  3 +--
 src/lj_crecord.c                               |  6 ++++--
 test/tarantool-tests/fix-cdata-concat.test.lua | 15 +++++++++++++++
 3 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 test/tarantool-tests/fix-cdata-concat.test.lua

diff --git a/src/lj_carith.c b/src/lj_carith.c
index 218abd26..04c18054 100644
--- a/src/lj_carith.c
+++ b/src/lj_carith.c
@@ -265,7 +265,7 @@ int lj_carith_op(lua_State *L, MMS mm)
 {
   CTState *cts = ctype_cts(L);
   CDArith ca;
-  if (carith_checkarg(L, cts, &ca)) {
+  if (carith_checkarg(L, cts, &ca) && mm != MM_len && mm != MM_concat) {
     if (carith_int64(L, cts, &ca, mm) || carith_ptr(L, cts, &ca, mm)) {
       copyTV(L, &G(L)->tmptv2, L->top-1);  /* Remember for trace recorder. */
       return 1;
@@ -347,7 +347,6 @@ uint64_t lj_carith_check64(lua_State *L, int narg, CTypeID *id)
   }
 }
 
-
 /* -- 64 bit integer arithmetic helpers ----------------------------------- */
 
 #if LJ_32 && LJ_HASJIT
diff --git a/src/lj_crecord.c b/src/lj_crecord.c
index 0d7b71f0..3d562d9a 100644
--- a/src/lj_crecord.c
+++ b/src/lj_crecord.c
@@ -1546,8 +1546,10 @@ void LJ_FASTCALL recff_cdata_arith(jit_State *J, RecordFFData *rd)
   }
   {
     TRef tr;
-    if (!(tr = crec_arith_int64(J, sp, s, (MMS)rd->data)) &&
-	!(tr = crec_arith_ptr(J, sp, s, (MMS)rd->data)) &&
+    MMS mm = (MMS)rd->data;
+    if ((mm == MM_len || mm == MM_concat ||
+	 (!(tr = crec_arith_int64(J, sp, s, mm)) &&
+	  !(tr = crec_arith_ptr(J, sp, s, mm)))) &&
 	!(tr = crec_arith_meta(J, sp, s, cts, rd)))
       return;
     J->base[0] = tr;
diff --git a/test/tarantool-tests/fix-cdata-concat.test.lua b/test/tarantool-tests/fix-cdata-concat.test.lua
new file mode 100644
index 00000000..aaeb36fa
--- /dev/null
+++ b/test/tarantool-tests/fix-cdata-concat.test.lua
@@ -0,0 +1,15 @@
+local tap = require('tap')
+
+-- Test file to demonstrate incorrect behaviour of cdata
+-- concatenation in LuaJIT.
+-- See also
+-- https://www.freelists.org/post/luajit/cdata-concatenation.
+local test = tap.test('cdata-concat')
+test:plan(1)
+
+local r, e = pcall(function()
+  return 1LL .. 2LL
+end)
+test:ok(not r and e:match('attempt to concatenate'), 'cdata concatenation')
+
+os.exit(test:check() and 0 or 1)
-- 
2.34.1