Segmentation fault in function mjs_stack_size (at mjs.c:7849)

[Vancir]

I found a segmentation fault bug while mjs (latest, b1b6eac) executes the PoC on Ubuntu 20.04.

Download the PoC: mjs_segv_mjs7849.zip

ASAN Report

==866928==ERROR: AddressSanitizer: SEGV on unknown address 0x0000000000d8 (pc 0x0000004dd2e8 bp 0x7ffdde783148 sp 0x7ffdde783148 T0)
==866928==The signal is caused by a READ memory access.
==866928==Hint: address points to the zero page.
    #0 0x4dd2e8 in mjs_stack_size /data/song/projects/latest-programs/mjs/BUILD/mjs.c:7849:13
    #1 0x4dd040 in vptr /data/song/projects/latest-programs/mjs/BUILD/mjs.c:7853:14
    #2 0x4dd317 in mjs_getretvalpos /data/song/projects/latest-programs/mjs/BUILD/mjs.c:7810:21
    #3 0x4dd441 in mjs_return /data/song/projects/latest-programs/mjs/BUILD/mjs.c:7837:13
    #4 0x4db66c in mjs_ffi_cb_free /data/song/projects/latest-programs/mjs/BUILD/mjs.c:10140:3
    #5 0x4dd8ee in mjs_exec_internal /data/song/projects/latest-programs/mjs/BUILD/mjs.c:9044:5
    #6 0x4ddaeb in mjs_exec_file /data/song/projects/latest-programs/mjs/BUILD/mjs.c:9067:11
    #7 0x4e1df7 in main /data/song/projects/latest-programs/mjs/BUILD/mjs.c:11406:13
    #8 0x7f236f6dfd8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #9 0x7f236f6dfe3f in __libc_start_main csu/../csu/libc-start.c:392:3
    #10 0x41f344 in _start (/data/song/projects/latest-programs/mjs/mjs-bin+0x41f344)

Steps to reproduce

git clone https://github.com/cesanta/mjs.git
cd mjs
clang -g -O1 -fsanitize=address -fno-omit-frame-pointer -Wno-error -DMJS_MAIN mjs.c -dl -o mjs_asan
./mjs_asan -f PoC