UBSan: hatrack: hash: set: null pointer passed as argument 1, which is declared to never be null

[ee7]

With:

• The latest commit on libcon4m main (de5b659) or jtv/parity-push (4f6ccbe)
• x86_64
• Linux 6.10.4
• glibc 2.40
• Clang 18.1.8
• Profile dev

Building c4test with UBSan enabled and then running it produces 500+ lines of output like:

../src/hatrack/hash/set.c:258:15: runtime error: null pointer passed as argument 1, which is declared to never be null
/usr/include/stdlib.h:971:30: note: nonnull attribute specified here
    #0 0x5899b1111647 in hatrack_set_items_base libcon4m/src/hatrack/hash/set.c:258:9
    #1 0x5899b1111ea1 in hatrack_set_items_sort libcon4m/src/hatrack/hash/set.c:305:12
    #2 0x5899b0fa6772 in c4m_set_to_xlist libcon4m/src/adts/set.c:158:38
    #3 0x5899b11430a6 in process_branch_exit libcon4m/src/compiler/cfg.c:497:30
    #4 0x5899b113cd67 in cfg_process_node libcon4m/src/compiler/cfg.c:633:9
    #5 0x5899b113d1a0 in cfg_process_node libcon4m/src/compiler/cfg.c:644:9
    #6 0x5899b113c070 in cfg_process_node libcon4m/src/compiler/cfg.c:577:31
    #7 0x5899b113d62a in cfg_process_node libcon4m/src/compiler/cfg.c:656:9
    #8 0x5899b113c070 in cfg_process_node libcon4m/src/compiler/cfg.c:577:31
    #9 0x5899b113b154 in c4m_cfg_analyze libcon4m/src/compiler/cfg.c:744:5
    #10 0x5899b106c882 in c4m_check_pass libcon4m/src/compiler/check_pass.c:3320:13
    #11 0x5899b1016fc5 in c4m_compile_from_entry_point libcon4m/src/compiler/compile.c:467:5
    #12 0x5899b0f07197 in execute_test libcon4m/src/harness/con4m_base/run.c:11:11
    #13 0x5899b0f05674 in run_one_item libcon4m/src/harness/con4m_base/run.c:61:29
    #14 0x5899b0f0535a in c4m_run_expected_value_tests libcon4m/src/harness/con4m_base/run.c:152:18
    #15 0x5899b0f01cdb in main libcon4m/src/harness/con4m_base/test.c:44:5
    #16 0x7fd148d45e07 in __libc_start_call_main /usr/src/debug/glibc/glibc/csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #17 0x7fd148d45ecb in __libc_start_main /usr/src/debug/glibc/glibc/csu/../csu/libc-start.c:360:3
    #18 0x5899b0ecf7b4 in _start (libcon4m/build_dev/c4test+0x14f7b4) (BuildId: eb75f65a7b383149176b9e55cbbfdfd116868794)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/hatrack/hash/set.c:258:15 

One test file that triggered this was basic05.c4m.

It looks like qsort may be called with a null view at one call site:

libcon4m/src/hatrack/hash/set.c

Lines 257 to 262 in de5b659

	if (sort) {
	qsort(view,
	*num,
	sizeof(hatrack_set_view_t),
	hatrack_set_epoch_sort_cmp);
	}

which makes UBSan complain on machines where qsort specifies that the first argument must not be null:

    /* Sort NMEMB elements of BASE, of SIZE bytes each,
       using COMPAR to perform the comparisons.  */
    extern void qsort (void *__base, size_t __nmemb, size_t __size,
              __compar_fn_t __compar) __nonnull ((1, 4));

This is pretty noisy, and will only get more noisy as more test cases are added. I'll make a PR, in case the simplest attempt at a fix works.