[Tarantool-patches] [PATCH luajit 3/4] ARM64: Fix xpcall() error case.

[Sergey Kaplun]

From: Mike Pall <mike>

Thanks to Stefan Pejic.

(cherry picked from commit 33082a6f4778aa152f6a4a684a7fe79436f1ecb6)

Premature incrementing VM's BASE register before switch to fff_fallback
handler during processing `xpcall()` fast function leads to incorrect
L->base value in case, when `xpcall()` calls without a second argument
or if it equals nil (see <301-basic.t> test in lua-Harness test suite).
While further error processing it leads to crash, due to stack
inconsistency.

This patch moves BASE incrementing after possible switching to
fallback handler.

Sergey Kaplun:
* added the description for the problem

Part of tarantool/tarantool#6093
Part of tarantool/tarantool#5629
---
 src/vm_arm64.dasc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/vm_arm64.dasc b/src/vm_arm64.dasc
index 6bf59509..e16a77ab 100644
--- a/src/vm_arm64.dasc
+++ b/src/vm_arm64.dasc
@@ -1186,12 +1186,12 @@ static void build_subroutines(BuildCtx *ctx)
   |   subs NARGS8:RC, NARGS8:RC, #16
   |   blo ->fff_fallback
   |    mov RB, BASE
-  |    add BASE, BASE, #24
   |     asr ITYPE, CARG2, #47
   |  ubfx TMP0w, TMP0w, #HOOK_ACTIVE_SHIFT, #1
   |     cmn ITYPE, #-LJ_TFUNC
   |  add PC, TMP0, #24+FRAME_PCALL
   |     bne ->fff_fallback		// Traceback must be a function.
+  |    add BASE, BASE, #24
   |     stp CARG2, CARG1, [RB]		// Swap function and traceback.
   |   cbz NARGS8:RC, ->vm_call_dispatch
   |  b <1
-- 
2.31.0