I used CFLAGS="-DNDEBUG -g2 -O1 -fsanitize=undefined". I built the library, then ran a 'make test V=1'. The output presented to the user looks OK. However, it looks like UBsan found some undefined behavior:
libunistring-0.9.10$ grep -IR 'runtime error' tests/test-u8-width-linebreaks.log:unilbrk/u8-possible-linebreaks.c:49:3: runtime error: null pointer passed as argument 1, which is declared to never be null tests/test-u32-to-u8.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-numeric.log:unictype/numeric.c:52:54: runtime error: left shift of 34927 by 16 places cannot be represented in type 'int' tests/test-nfkc.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u8-tolower.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u16-to-u8.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-nfkd.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u8-casefold.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/unicase/test-ulc-casecmp2.sh.log:uniconv/u8-conv-from-enc.c:89:7: runtime error: null pointer passed as argument 2, which is declared to never be null tests/unicase/test-ulc-casecoll2.sh.log:uniconv/u8-conv-from-enc.c:89:7: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-nfc.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u8-totitle.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-nfd.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u16-possible-linebreaks.log:unilbrk/u16-possible-linebreaks.c:49:3: runtime error: null pointer passed as argument 1, which is declared to never be null tests/test-u16-width-linebreaks.log:unilbrk/u16-possible-linebreaks.c:49:3: runtime error: null pointer passed as argument 1, which is declared to never be null tests/test-u8-toupper.log:unistr/u8-cmp.c:38:10: runtime error: null pointer passed as argument 2, which is declared to never be null tests/test-u8-possible-linebreaks.log:unilbrk/u8-possible-linebreaks.c:49:3: runtime error: null pointer passed as argument 1, which is declared to never be null "runtime error: null pointer passed as argument <N>" is generally benign under glibc, but musl is a different story. Musl believes in early failures, and probably will deference the NULL pointer and crash. Be careful of these in the long run. The compiler is free to drop the code because it is undefined behavior. My personal experience is, little findings like these are the cause of obscure failures, like self test failures on 32-bit ARM with GCC 5.0-5.2, while other platforms will be OK.
