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SubjectRe: 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@linaro.org>
>
> 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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