[Tarantool-patches] [PATCH luajit] FFI: Fix recording of union initialization.

[Maksim Kokryashkin]

From: Mike Pall <mike>

Thanks to Alex Shpilkin.

(cherry-picked from commit 56c04accf975bff2519c34721dccbbdb7b8e6963)

As stated here[1], only the first field of a union can be
initialized with a flat initializer. However, before this
patch, on-trace initialization instructions were emitted
for other union members too, overwriting the previous
initialization values.

This patch fixes the mentioned behavior by preventing
initialization of members other than the first one.

[1]: https://luajit.org/ext_ffi_semantics.html#init

Maxim Kokryashkin:
* added the description and the test for the problem

Part of tarantool/tarantool#8825
---
Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-128-fix-union-init
PR: https://github.com/tarantool/tarantool/pull/8867
Original LuaJIT PR: https://github.com/LuaJIT/LuaJIT/pull/650

 src/lj_crecord.c                               |  5 +++++
 .../lj-128-fix-union-init.test.lua             | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 test/tarantool-tests/lj-128-fix-union-init.test.lua

diff --git a/src/lj_crecord.c b/src/lj_crecord.c
index 0008a865..ffe995f4 100644
--- a/src/lj_crecord.c
+++ b/src/lj_crecord.c
@@ -1065,6 +1065,11 @@ static void crec_alloc(jit_State *J, RecordFFData *rd, CTypeID id)
 	  dp = emitir(IRT(IR_ADD, IRT_PTR), trcd,
 		      lj_ir_kintp(J, df->size + sizeof(GCcdata)));
 	  crec_ct_tv(J, dc, dp, sp, sval);
+	  if ((d->info & CTF_UNION)) {
+	    if (d->size != dc->size)  /* NYI: partial init of union. */
+	      lj_trace_err(J, LJ_TRERR_NYICONV);
+	    break;
+	  }
 	} else if (!ctype_isconstval(df->info)) {
 	  /* NYI: init bitfields and sub-structures. */
 	  lj_trace_err(J, LJ_TRERR_NYICONV);
diff --git a/test/tarantool-tests/lj-128-fix-union-init.test.lua b/test/tarantool-tests/lj-128-fix-union-init.test.lua
new file mode 100644
index 00000000..6a49cec8
--- /dev/null
+++ b/test/tarantool-tests/lj-128-fix-union-init.test.lua
@@ -0,0 +1,18 @@
+local tap = require('tap')
+local test = tap.test('lj-128-fix-union-init'):skipcond({
+  ['Test requires JIT enabled'] = not jit.status(),
+})
+
+local NITERATIONS = 4
+
+test:plan(NITERATIONS)
+
+local ffi = require('ffi')
+local union_type = ffi.typeof('union { uint32_t u; float f; }')
+
+jit.opt.start('hotloop=1')
+for i = 1, NITERATIONS do
+  test:ok(union_type(i).u == i)
+end
+
+os.exit(test:check() and 0 or 1)
-- 
2.39.2 (Apple Git-143)