$ clang -g -fno-omit-frame-pointer -fsanitize=address geohash_test.c geohash.c
./a.out
=================================================================
==145148==ERROR: AddressSanitizer: global-buffer-overflow on address 0x55ba71db93e0 at pc 0x55ba71cf095b bp 0x7fff48e04d10 sp 0x7fff48e044c0
READ of size 33 at 0x55ba71db93e0 thread T0
#0 0x55ba71cf095a in __interceptor_strlen.part.0 (/home/mpech/libgeohash/a.out+0x6895a)
#1 0x55ba71d8326f in index_for_char /home/mpech/libgeohash/geohash.c:83:25
#2 0x55ba71d83f1e in geohash_decode /home/mpech/libgeohash/geohash.c:209:33
#3 0x55ba71d826cd in main /home/mpech/libgeohash/geohash_test.c:84:22
#4 0x7f83bb758151 in __libc_start_main (/usr/lib/libc.so.6+0x28151)
#5 0x55ba71ca919d in _start (/home/mpech/libgeohash/a.out+0x2119d)
0x55ba71db93e0 is located 0 bytes to the right of global variable 'char_map' defined in 'geohash.c:59:13' (0x55ba71db93c0) of size 32
SUMMARY: AddressSanitizer: global-buffer-overflow (/home/mpech/libgeohash/a.out+0x6895a) in __interceptor_strlen.part.0
Shadow bytes around the buggy address:
0x0ab7ce3af220: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af230: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af240: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af250: f9 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 f9 f9 f9 f9
0x0ab7ce3af260: 00 00 00 00 f9 f9 f9 f9 00 00 00 00 f9 f9 f9 f9
=>0x0ab7ce3af270: 00 00 00 00 f9 f9 f9 f9 00 00 00 00[f9]f9 f9 f9
0x0ab7ce3af280: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af290: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af2a0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af2b0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
0x0ab7ce3af2c0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
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
Shadow gap: cc
==145148==ABORTING
make: *** [Makefile:12: test] Error 1
