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

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Date:   Tue, 7 Mar 2023 11:28:39 -0800
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, <linux-api@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        <lkft-triage@...ts.linaro.org>
CC:     Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Len Brown" <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
        Stas Sergeev <stsp@...t.ru>, Arnd Bergmann <arnd@...db.de>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: selftests: sigaltstack: sas # exit=1 - # Bail out! SP is not on
 sigaltstack - on clang build

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@...aro.org>
> 
> Test log:
> ----------
> 
> Linux version 6.3.0-rc1-next-20230307 (tuxmake@...make) (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@...make)
> (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