A cursory look at the strace shows:

[127] test_tasks_ada % strace -f ./adatests 
execve("./adatests", ["./adatests"], [/* 66 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7f2efdda9ba8) = 0
set_tid_address(0x7f2efdda9be0)         = 23157
mprotect(0x7f2efdda6000, 4096, PROT_READ) = 0
mprotect(0x64b000, 4096, PROT_READ)     = 0
rt_sigprocmask(SIG_UNBLOCK, [RT_1 RT_2], NULL, 8) = 0
rt_sigaction(SIGABRT, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, NULL, 8) = 0
rt_sigaction(SIGFPE, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, NULL, 8) = 0
rt_sigaction(SIGILL, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, NULL, 8) = 0
rt_sigaction(SIGBUS, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, NULL, 8) = 0
sigaltstack({ss_sp=0x6530e0, ss_flags=0, ss_size=16384}, NULL) = 0
rt_sigaction(SIGSEGV, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_STACK|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, NULL, 8) = 0
clock_getres(CLOCK_REALTIME, {tv_sec=0, tv_nsec=1}) = 0
sched_getaffinity(0, 128, [0, 1])       = 64
rt_sigaction(SIGFPE, {sa_handler=0x40f310, sa_mask=[ILL BUS FPE SEGV], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, 8) = 0
rt_sigaction(SIGILL, {sa_handler=0x40f310, sa_mask=[ILL BUS FPE SEGV], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, 8) = 0
rt_sigaction(SIGSEGV, {sa_handler=0x40f310, sa_mask=[ILL BUS FPE SEGV], sa_flags=SA_RESTORER|SA_STACK|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_STACK|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, 8) = 0
rt_sigaction(SIGBUS, {sa_handler=0x40f310, sa_mask=[ILL BUS FPE SEGV], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, 8) = 0
gettid()                                = 23157
sigaltstack({ss_sp=0x6530e0, ss_flags=0, ss_size=16384}, NULL) = 0
rt_sigaction(SIGABRT, {sa_handler=0x406e50, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f2efdb61f5d}, {sa_handler=0x42d690, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_NODEFER|SA_SIGINFO, sa_restorer=0x7f2efdb61f5d}, 8) = 0
sched_getaffinity(0, 128, [0, 1])       = 64
sched_getaffinity(0, 128, [0, 1])       = 64
sched_setscheduler(23157, SCHED_OTHER, [0]) = 0
sched_getaffinity(0, 128, [0, 1])       = 64
fstat(2, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
fstat(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
writev(1, [{iov_base="", iov_len=0}, {iov_base="Creating  10 tasks.\n", iov_len=20}], 2Creating  10 tasks.
) = 20
brk(NULL)                               = 0x10f2000
brk(0x10f5000)                          = 0x10f5000
rt_sigprocmask(SIG_UNBLOCK, [RT_1 RT_2], NULL, 8) = 0
mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efd911000
mprotect(0x7f2efd912000, 2117632, PROT_READ|PROT_WRITE) = 0
clone(strace: Process 23158 attached
child_stack=0x7f2efdb16ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efdb16b20, tls=0x7f2efdb16ae8) = 23158
[pid 23158] gettid()                    = 23158
[pid 23158] prctl(PR_SET_NAME, "a(1)" <unfinished ...>
[pid 23157] sched_setscheduler(23158, SCHED_OTHER, [0] <unfinished ...>
[pid 23158] <... prctl resumed> )       = 0
[pid 23157] <... sched_setscheduler resumed> ) = 0
[pid 23158] sigaltstack({ss_sp=0x7f2efdb12a70, ss_flags=0, ss_size=16384},  <unfinished ...>
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULL <unfinished ...>
[pid 23158] <... sigaltstack resumed> NULL) = 0
[pid 23158] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23158] <... futex resumed> )       = 1
[pid 23157] futex(0x7f2efddaa31c, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23158] futex(0x7f2efddaa31c, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = -1 EAGAIN (Resource temporarily unavailable)
[pid 23158] <... futex resumed> )       = 0
[pid 23157] brk(0x10f6000)              = 0x10f6000
[pid 23157] brk(0x10f9000)              = 0x10f9000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efd70b000
[pid 23157] mprotect(0x7f2efd70c000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(strace: Process 23159 attached
child_stack=0x7f2efd910ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efd910b20, tls=0x7f2efd910ae8) = 23159
[pid 23159] gettid()                    = 23159
[pid 23159] prctl(PR_SET_NAME, "a(2)")  = 0
[pid 23159] sigaltstack({ss_sp=0x7f2efd90ca70, ss_flags=0, ss_size=16384},  <unfinished ...>
[pid 23157] sched_setscheduler(23159, SCHED_OTHER, [0] <unfinished ...>
[pid 23159] <... sigaltstack resumed> NULL) = 0
[pid 23157] <... sched_setscheduler resumed> ) = 0
[pid 23159] futex(0x64f244, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23157] futex(0x64f244, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23159] <... futex resumed> )       = 0
[pid 23157] brk(0x10fc000)              = 0x10fc000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efd505000
[pid 23157] mprotect(0x7f2efd506000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efd70aab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efd70ab20, tls=0x7f2efd70aae8) = 23160
[pid 23157] sched_setscheduler(23160, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23160 attached
 <unfinished ...>
[pid 23160] gettid()                    = 23160
[pid 23160] prctl(PR_SET_NAME, "a(3)")  = 0
[pid 23160] sigaltstack({ss_sp=0x7f2efd706a70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23160] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] brk(0x10fd000)              = 0x10fd000
[pid 23157] brk(0x1100000)              = 0x1100000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efd2ff000
[pid 23157] mprotect(0x7f2efd300000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efd504ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efd504b20, tls=0x7f2efd504ae8) = 23161
[pid 23157] sched_setscheduler(23161, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23161 attached
 <unfinished ...>
[pid 23161] gettid()                    = 23161
[pid 23161] prctl(PR_SET_NAME, "a(4)")  = 0
[pid 23161] sigaltstack({ss_sp=0x7f2efd500a70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23161] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] futex(0x7f2efddaa31c, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23161] futex(0x7f2efddaa31c, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23161] <... futex resumed> )       = 1
[pid 23157] brk(0x1103000)              = 0x1103000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efd0f9000
[pid 23157] mprotect(0x7f2efd0fa000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efd2feab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efd2feb20, tls=0x7f2efd2feae8) = 23162
[pid 23157] sched_setscheduler(23162, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23162 attached
 <unfinished ...>
[pid 23162] gettid()                    = 23162
[pid 23162] prctl(PR_SET_NAME, "a(5)")  = 0
[pid 23162] sigaltstack({ss_sp=0x7f2efd2faa70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23162] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] brk(0x1106000)              = 0x1106000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efcef3000
[pid 23157] mprotect(0x7f2efcef4000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efd0f8ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efd0f8b20, tls=0x7f2efd0f8ae8) = 23163
[pid 23157] sched_setscheduler(23163, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23163 attached
 <unfinished ...>
[pid 23163] gettid()                    = 23163
[pid 23163] prctl(PR_SET_NAME, "a(6)")  = 0
[pid 23163] sigaltstack({ss_sp=0x7f2efd0f4a70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23163] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23163] <... futex resumed> )       = 1
[pid 23157] futex(0x7f2efddaa31c, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23163] futex(0x7f2efddaa31c, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23163] <... futex resumed> )       = 1
[pid 23157] brk(0x1107000)              = 0x1107000
[pid 23157] brk(0x110a000)              = 0x110a000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efcced000
[pid 23157] mprotect(0x7f2efccee000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efcef2ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efcef2b20, tls=0x7f2efcef2ae8) = 23164
[pid 23157] sched_setscheduler(23164, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23164 attached
 <unfinished ...>
[pid 23164] gettid()                    = 23164
[pid 23164] prctl(PR_SET_NAME, "a(7)")  = 0
[pid 23164] sigaltstack({ss_sp=0x7f2efceeea70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23164] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] brk(0x110d000)              = 0x110d000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efcae7000
[pid 23157] mprotect(0x7f2efcae8000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efccecab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efccecb20, tls=0x7f2efccecae8) = 23165
[pid 23157] sched_setscheduler(23165, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23165 attached
 <unfinished ...>
[pid 23165] gettid()                    = 23165
[pid 23165] prctl(PR_SET_NAME, "a(8)")  = 0
[pid 23165] sigaltstack({ss_sp=0x7f2efcce8a70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23165] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] futex(0x7f2efddaa31c, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23165] futex(0x7f2efddaa31c, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23165] <... futex resumed> )       = 1
[pid 23157] brk(0x110e000)              = 0x110e000
[pid 23157] brk(0x1111000)              = 0x1111000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efc8e1000
[pid 23157] mprotect(0x7f2efc8e2000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efcae6ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efcae6b20, tls=0x7f2efcae6ae8) = 23166
[pid 23157] sched_setscheduler(23166, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23166 attached
 <unfinished ...>
[pid 23166] gettid()                    = 23166
[pid 23166] prctl(PR_SET_NAME, "a(9)")  = 0
[pid 23166] sigaltstack({ss_sp=0x7f2efcae2a70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23166] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1) = 1
[pid 23157] <... futex resumed> )       = 0
[pid 23157] brk(0x1114000)              = 0x1114000
[pid 23157] mmap(NULL, 2121728, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2efc6db000
[pid 23157] mprotect(0x7f2efc6dc000, 2117632, PROT_READ|PROT_WRITE) = 0
[pid 23157] clone(child_stack=0x7f2efc8e0ab8, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|0x400000, parent_tidptr=0x7f2efc8e0b20, tls=0x7f2efc8e0ae8) = 23167
[pid 23157] sched_setscheduler(23167, SCHED_OTHER, [0]) = 0
[pid 23157] futex(0x7ffee67e6cd4, FUTEX_WAIT_PRIVATE, 2, NULLstrace: Process 23167 attached
 <unfinished ...>
[pid 23167] gettid()                    = 23167
[pid 23167] prctl(PR_SET_NAME, "a(10)") = 0
[pid 23167] sigaltstack({ss_sp=0x7f2efc8dca70, ss_flags=0, ss_size=16384}, NULL) = 0
[pid 23167] futex(0x7ffee67e6cd4, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23167] <... futex resumed> )       = 1
[pid 23157] futex(0x7f2efddaa31c, FUTEX_WAIT_PRIVATE, 2147483664, NULL <unfinished ...>
[pid 23167] futex(0x7f2efddaa31c, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 23157] <... futex resumed> )       = 0
[pid 23167] <... futex resumed> )       = 1
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="PASS: created max_tasks.\n", iov_len=25}], 2PASS: created max_tasks.
) = 25
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="Aborting  10 tasks.\n", iov_len=20}], 2Aborting  10 tasks.
) = 20
[pid 23157] tkill(23158, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  1 NOT aborted.\n", iov_len=27}], 2FAIL: Task  1 NOT aborted.
) = 27
[pid 23157] tkill(23159, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  2 NOT aborted.\n", iov_len=27}], 2FAIL: Task  2 NOT aborted.
) = 27
[pid 23157] tkill(23160, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  3 NOT aborted.\n", iov_len=27}], 2FAIL: Task  3 NOT aborted.
) = 27
[pid 23157] tkill(23161, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  4 NOT aborted.\n", iov_len=27}], 2FAIL: Task  4 NOT aborted.
) = 27
[pid 23157] tkill(23162, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  5 NOT aborted.\n", iov_len=27}], 2FAIL: Task  5 NOT aborted.
) = 27
[pid 23157] tkill(23163, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  6 NOT aborted.\n", iov_len=27}], 2FAIL: Task  6 NOT aborted.
) = 27
[pid 23157] tkill(23164, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  7 NOT aborted.\n", iov_len=27}], 2FAIL: Task  7 NOT aborted.
) = 27
[pid 23157] tkill(23165, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  8 NOT aborted.\n", iov_len=27}], 2FAIL: Task  8 NOT aborted.
) = 27
[pid 23157] tkill(23166, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  9 NOT aborted.\n", iov_len=27}], 2FAIL: Task  9 NOT aborted.
) = 27
[pid 23157] tkill(23167, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  10 NOT aborted.\n", iov_len=28}], 2FAIL: Task  10 NOT aborted.
 <unfinished ...>
[pid 23167] --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=23157, si_uid=1000} ---
[pid 23157] <... writev resumed> )      = 28
[pid 23161] --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=23157, si_uid=1000} ---
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: after abort:  10 tasks ali"..., iov_len=36}], 2FAIL: after abort:  10 tasks alive.
) = 36
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="Will abort main program with C's"..., iov_len=38}], 2Will abort main program with C's exit
) = 38
[pid 23157] exit_group(0 <unfinished ...>
[pid 23167] rt_sigreturn({mask=[]} <ptrace(SYSCALL):No such process>
[pid 23157] <... exit_group resumed>)   = ?
[pid 23167] <... rt_sigreturn resumed>) = ?
[pid 23167] +++ exited with 0 +++
[pid 23163] +++ exited with 0 +++
[pid 23161] +++ exited with 0 +++
[pid 23158] +++ exited with 0 +++
[pid 23165] +++ exited with 0 +++
[pid 23166] +++ exited with 0 +++
[pid 23164] +++ exited with 0 +++
[pid 23162] +++ exited with 0 +++
[pid 23160] +++ exited with 0 +++
[pid 23159] +++ exited with 0 +++
+++ exited with 0 +++

More precisely, one of the issues seems to be that abort seems to be delivered to the child thread after the check for 'thread aborted' has already been done:
[pid 23157] tkill(23167, SIGABRT)       = 0
[pid 23157] writev(1, [{iov_base="", iov_len=0}, {iov_base="FAIL: Task  10 NOT aborted.\n", iov_len=28}], 2FAIL: Task  10 NOT aborted.
 <unfinished ...>
[pid 23167] --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=23157, si_uid=1000} ---

The abort is ignored because of:
line 183 at http://www.loper-os.org/pub/ffa/gnatology/ave1gnat/s-taprop-linux__adb.htm 

Some more info about this ZCX seems to be here:
https://docs.adacore.com/gnat_ugn-docs/html/gnat_ugn/gnat_ugn/platform_specific_information.html