Hi, This is what happens when I try to build XEmacs 21.4.24 with the address sanitizer enabled. This is the relevant ./configure switch: '--cflags=-std=gnu89 -g -fsanitize=address -fno-omit-frame-pointer' Dumping under the name xemacs ================================================================= ==56900==ERROR: AddressSanitizer: global-buffer-overflow on address 0x0001008b8da8 at pc 0x000100cba91a bp 0x7fff5fbf8110 sp 0x7fff5fbf78c8 READ of size 48 at 0x0001008b8da8 thread T0 #0 0x100cba919 in __asan_memcpy (libclang_rt.asan_osx_dynamic.dylib:x86_64+0x50919) #1 0x10015534c in pdump_dump_data dumper.c:634 #2 0x100154cab in pdump_scan_by_alignment dumper.c:828 #3 0x100153e8a in pdump dumper.c:1060 #4 0x1000fc22d in Fdump_emacs emacs.c:3217 #5 0x100100189 in Feval eval.c:3335 #6 0x100102f17 in Fprogn eval.c:775 #7 0x1000ffa3d in Feval eval.c:3308 #8 0x100102b83 in Fif eval.c:691 #9 0x1000ffa3d in Feval eval.c:3308 #10 0x100101e6c in Feval eval.c:3414 #11 0x1005312e7 in readevalloop lread.c:1449 #12 0x10052c86b in Fload_internal lread.c:737 #13 0x1001007a6 in Feval eval.c:3335 #14 0x10010d82b in condition_case_1 eval.c:1652 #15 0x10007f7cf in top_level_1 cmdloop.c:206 #16 0x10010c69b in internal_catch eval.c:1318 #17 0x10007ebec in initial_command_loop cmdloop.c:285 #18 0x1000f2d84 in xemacs_21_4_24_i386_apple_darwin14_5_0 emacs.c:2460 #19 0x1000fa5b5 in main emacs.c:2829 #20 0x7fff8818b5c8 in start (libdyld.dylib:x86_64+0x35c8) 0x0001008b8da8 is located 0 bytes to the right of global variable 'guts_of_unbound_marker' defined in 'symbols.c:3238:40' (0x1008b8d80) of size 40 SUMMARY: AddressSanitizer: global-buffer-overflow (libclang_rt.asan_osx_dynamic.dylib:x86_64+0x50919) in __asan_memcpy Shadow bytes around the buggy address: 0x100020117160: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100020117170: 00 00 f9 f9 f9 f9 f9 f9 00 00 00 f9 f9 f9 f9 f9 0x100020117180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f9 0x100020117190: f9 f9 f9 f9 00 00 00 00 00 00 f9 f9 f9 f9 f9 f9 0x1000201171a0: 00 00 00 00 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9 =>0x1000201171b0: 00 00 00 00 00[f9]f9 f9 f9 f9 f9 f9 00 00 00 00 0x1000201171c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1000201171d0: f9 f9 f9 f9 00 00 00 00 00 00 00 00 01 f9 f9 f9 0x1000201171e0: f9 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00 0x1000201171f0: 00 00 00 00 f9 f9 f9 f9 00 00 00 00 00 00 00 00 0x100020117200: 00 00 00 00 f9 f9 f9 f9 00 00 00 00 00 00 00 00 Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe Left alloca redzone: ca Right alloca redzone: cb ==56900==ABORTING -- Johann I'm not from the internet, I just work there.