UBSAN: function pointer casting in dt_htab

[thesamesam]

With Clang's UBSAN:

$ export UBSAN_OPTIONS="print_stacktrace=1:halt_on_error=0"
$ make CC=clang CFLAGS="-O2 -fsanitize=undefined -static-libsan -ggdb3" LDFLAGS="-fsanitize=undefined -static-libsan" verbose=yes -j32 -k
[...]
clang -O2 -fsanitize=undefined -static-libsan -ggdb3 -std=gnu99 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_DT_VERSION=\"2.0.1\" -Iuts/common -fsanitize=undefined -static-libsan -o /home/sam/git/dtrace-utils-bad/build/usdt-tst-argmap /home/sam/git/dtrace-utils-bad/build/test-triggers--usdt-tst-argmap.o /home/sam/git/dtrace-utils-bad/build/test-triggers--usdt-tst-argmap-prov.o -L/home/sam/git/dtrace-utils-bad/build
rm -f test/triggers/usdt-tst-argmap
ln -s /home/sam/git/dtrace-utils-bad/build/usdt-tst-argmap test/triggers/usdt-tst-argmap
libdtrace/dt_htab.c:238:18: runtime error: call to function prv_hval through pointer to incorrect function type 'unsigned int (*)(const void *)'
/home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:54:1: note: prv_hval defined here
    #0 0x7fc4f086a4ab in dt_htab_delete /home/sam/git/dtrace-utils-bad/libdtrace/dt_htab.c:238:18
    #1 0x7fc4f0910dcb in dt_probe_destroy /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:354:3
    #2 0x7fc4f091c81e in dt_probe_fini /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:1334:3
    #3 0x7fc4f08bab46 in dtrace_close /home/sam/git/dtrace-utils-bad/libdtrace/dt_open.c:1313:2
    #4 0x55caac25000e in main /home/sam/git/dtrace-utils-bad/cmd/dtrace.c
    #5 0x7fc4f0389834  (/usr/lib64/libc.so.6+0x26834)
    #6 0x7fc4f03898e7 in __libc_start_main (/usr/lib64/libc.so.6+0x268e7)
    #7 0x55caac221ef4 in _start (/home/sam/git/dtrace-utils-bad/build/dtrace+0xcef4)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior libdtrace/dt_htab.c:238:18
libdtrace/dt_htab.c:248:7: runtime error: call to function prv_cmp through pointer to incorrect function type 'int (*)(const void *, const void *)'
/home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:54:1: note: prv_cmp defined here
    #0 0x7fc4f086a2cf in dt_htab_delete /home/sam/git/dtrace-utils-bad/libdtrace/dt_htab.c:248:7
    #1 0x7fc4f0910dcb in dt_probe_destroy /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:354:3
    #2 0x7fc4f091c81e in dt_probe_fini /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:1334:3
    #3 0x7fc4f08bab46 in dtrace_close /home/sam/git/dtrace-utils-bad/libdtrace/dt_open.c:1313:2
    #4 0x55caac25000e in main /home/sam/git/dtrace-utils-bad/cmd/dtrace.c
    #5 0x7fc4f0389834  (/usr/lib64/libc.so.6+0x26834)
    #6 0x7fc4f03898e7 in __libc_start_main (/usr/lib64/libc.so.6+0x268e7)
    #7 0x55caac221ef4 in _start (/home/sam/git/dtrace-utils-bad/build/dtrace+0xcef4)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior libdtrace/dt_htab.c:248:7
libdtrace/dt_htab.c:258:9: runtime error: call to function prv_del through pointer to incorrect function type 'void *(*)(void *, void *)'
/home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:54:1: note: prv_del defined here
    #0 0x7fc4f086a81a in dt_htab_delete /home/sam/git/dtrace-utils-bad/libdtrace/dt_htab.c:258:9
    #1 0x7fc4f0910dcb in dt_probe_destroy /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:354:3
    #2 0x7fc4f091c81e in dt_probe_fini /home/sam/git/dtrace-utils-bad/libdtrace/dt_probe.c:1334:3
    #3 0x7fc4f08bab46 in dtrace_close /home/sam/git/dtrace-utils-bad/libdtrace/dt_open.c:1313:2
    #4 0x55caac25000e in main /home/sam/git/dtrace-utils-bad/cmd/dtrace.c
    #5 0x7fc4f0389834  (/usr/lib64/libc.so.6+0x26834)
    #6 0x7fc4f03898e7 in __libc_start_main (/usr/lib64/libc.so.6+0x268e7)
    #7 0x55caac221ef4 in _start (/home/sam/git/dtrace-utils-bad/build/dtrace+0xcef4)

See https://maskray.me/blog/2022-12-18-control-flow-integrity#fsanitizefunction. Note that GCC's UBSAN doesn't yet include this. This is less important than the other sanitizer issues as I don't think CFI is really a priority for DTrace.