How do people feel about shipping the minimal UBSan runtime library[1]
in the base system? It takes very little to build (Makefile + a few
ifdefs that both jca@ and I hacked together). The library is tiny and
useful enough for finding UB in base.
% ls -l /usr/lib/clang/13.0.0/lib/libclang_rt.ubsan_minimal*
-r--r--r-- 1 root bin 51516 Feb 4 20:02
/usr/lib/clang/13.0.0/lib/libclang_rt.ubsan_minimal.a
% cd /usr/src/games/battlestar
% make obj && make clean; make LDFLAGS='-fsanitize=undefined
-fsanitize-minimal-runtime' COPTS='-g -fsanitize=undefined
-fsanitize-minimal-runtime -fno-wrapv'
% ./obj/battlestar
Version 4.2, fall 1984.
First Adventure game written by His Lordship, the honorable
Admiral D.W. Riggle
ubsan: shift-out-of-bounds
% egdb ./obj/battlestar
(gdb) b __ubsan_handle_shift_out_of_bounds_minimal
Breakpoint 1 at 0x23630: file
/usr/src/gnu/lib/libclang_rt/ubsan_minimal/../../../llvm/compiler-rt/lib/ubsan_minimal/ubsan_minimal_handlers.cpp,
line 104.
(gdb) bt
No stack.
(gdb) r
Starting program: /usr/obj/games/battlestar/battlestar
Version 4.2, fall 1984.
First Adventure game written by His Lordship, the honorable
Admiral D.W. Riggle
Breakpoint 1, __ubsan_handle_shift_out_of_bounds_minimal ()
at
/usr/src/gnu/lib/libclang_rt/ubsan_minimal/../../../llvm/compiler-rt/lib/ubsan_minimal/ubsan_minimal_handlers.cpp:104
104 HANDLER(shift_out_of_bounds, "shift-out-of-bounds")
(gdb) bt
#0 __ubsan_handle_shift_out_of_bounds_minimal ()
at
/usr/src/gnu/lib/libclang_rt/ubsan_minimal/../../../llvm/compiler-rt/lib/ubsan_minimal/ubsan_minimal_handlers.cpp:104
#1 0x000007434ee9f654 in initialize (filename=<optimized out>) at
/usr/src/games/battlestar/init.c:67
#2 0x000007434ee8af06 in main (argc=1, argv=<optimized out>) at
/usr/src/games/battlestar/battlestar.c:58
(gdb) up
#1 0x00000b1eddd2a654 in initialize (filename=<optimized out>) at
/usr/src/games/battlestar/init.c:67
67 SetBit(location[p->room].objects, p->obj);
(gdb) !grep SetBit extern.h
#define SetBit(array, index) (array[index/BITS] |= (1 << (index % BITS)))
Yup, the usual, shifting too far without 1U. Hence the patch:
--- a/games/battlestar/extern.h
+++ b/games/battlestar/extern.h
@@ -39,9 +39,9 @@
#define OUTSIDE (position > 68 && position < 246 && position !=
218)
#define rnd(x) arc4random_uniform(x)
#define max(a,b) ((a) < (b) ? (b) : (a))
-#define TestBit(array, index) (array[index/BITS] & (1 << (index % BITS)))
-#define SetBit(array, index) (array[index/BITS] |= (1 << (index % BITS)))
-#define ClearBit(array, index) (array[index/BITS] &= ~(1 << (index % BITS)))
+#define TestBit(array, index) (array[index/BITS] & (1U << (index % BITS)))
+#define SetBit(array, index) (array[index/BITS] |= (1U << (index % BITS)))
+#define ClearBit(array, index) (array[index/BITS] &= ~(1U << (index % BITS)))
/*
* These macros yield words to use with objects (followed but not preceded
* by spaces, or with no spaces if the expansion is the empty string).
OK to fix battlestar while we are at it?
[1] https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#minimal-runtime
