Re: selftests: sigaltstack: sas # exit=1 - # Bail out! SP is not on sigaltstack - on clang build

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On 3/6/2023 10:57 PM, Naresh Kamboju wrote:
kselftest: sigaltstack built with clang-16 getting failed but passed with
gcc-12 build. Please find more details about test logs on clang-16 and
gcc-12 and steps to reproduce locally on your machine by using tuxrun.

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>

Test log:
----------

Linux version 6.3.0-rc1-next-20230307 (tuxmake@tuxmake) (Debian clang
version 16.0.0 (++20230228093516+60692a66ced6-1~exp1~20230228093525.41),
Debian LLD 16.0.0) #1 SMP PREEMPT @1678159722
...
kselftest: Running tests in sigaltstack
TAP version 13
1..1
# selftests: sigaltstack: sas
# # [NOTE] the stack size is 21104
# TAP version 13
# 1..3
# ok 1 Initial sigaltstack state was SS_DISABLE
# Bail out! SP is not on sigaltstack
# # Planned tests != run tests (3 != 1)
# # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
not ok 1 selftests: sigaltstack: sas # exit=1
<snip>

Linux version 6.3.0-rc1-next-20230307 (tuxmake@tuxmake)
(aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils
for Debian) 2.40) #1 SMP PREEMPT @1678159736
...
kselftest: Running tests in sigaltstack
TAP version 13
1..1
# selftests: sigaltstack: sas
# # [NOTE] the stack size is 50080
# TAP version 13
# 1..3
# ok 1 Initial sigaltstack state was SS_DISABLE
# # [RUN] signal USR1
# ok 2 sigaltstack is disabled in sighandler
# # [RUN] switched to user ctx
# # [RUN] signal USR2
# # [OK] Stack preserved
# ok 3 sigaltstack is still SS_AUTODISARM after signal
# # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
ok 1 selftests: sigaltstack: sas

At glance, the log shows the altstack size difference between LLVM and GCC.

But, when I tried with the LLVM that I have,

    $ clang --version
    clang version 13.0.0 ...

it failed only with this compiler:

    $ rm sas;clang -o sas sas.c;./sas
    # [NOTE]        the stack size is 8192
    TAP version 13
    1..3
    ok 1 Initial sigaltstack state was SS_DISABLE
    Bail out! SP is not on sigaltstack
    # Planned tests != run tests (3 != 1)
    # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

    $ rm sas;gcc -o sas sas.c;./sas
    # [NOTE]        the stack size is 8192
    TAP version 13
    1..3
    ok 1 Initial sigaltstack state was SS_DISABLE
    # [RUN] signal USR1
    ok 2 sigaltstack is disabled in sighandler
    # [RUN] switched to user ctx
    # [RUN] signal USR2
    # [OK]  Stack preserved
    ok 3 sigaltstack is still SS_AUTODISARM after signal
    # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

The same is true with some old versions -- e.g. the one that came with commit 0c49ad415512 ("tools/testing/selftests/sigaltstack/sas.c: improve output of sigaltstack testcase"):

    $ rm sas;clang -o sas sas.c;./sas
    [OK]    Initial sigaltstack state was SS_DISABLE
    [FAIL]  SP is not on sigaltstack

    $ rm sas;gcc -o sas sas.c;./sas
    [OK]    Initial sigaltstack state was SS_DISABLE
    [RUN]   signal USR1
    [OK]    sigaltstack is disabled in sighandler
    [RUN]   switched to user ctx
    [RUN]   signal USR2
    [OK]    Stack preserved
    [OK]    sigaltstack is still SS_AUTODISARM after signal
    [OK]    Test passed

So, this test failure appears to have been there for a while. I think the LLVM folks need to take a look at it.

Thanks,
Chang



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