Re: selftest/vDSO: vdso_test_abi tests with gcc-13 and pass with clang-19

["Arnd Bergmann" <arnd@arndb.de>]

On Wed, Feb 12, 2025, at 15:29, Naresh Kamboju wrote:
> The kselftest-vDSO/vdso_test_abi test encounters failures when built
> and executed using GCC-13 on armv7 architecture.
> The issue has been observed on both TI X15 devices and QEMU-armv7.
>
> Interestingly, the same test passes without any issues when built using
> Clang-19.This failure is specific to GCC-13. but test case should have
> been failed on clang toolchain but it did not.

To clarify: the failure depends on how the toolchain is built:
for compilers using the default 32-bit time_t in glibc, ltp does
not notice a problem, but using gcc it will run into a testcase
bug because the vdso_test_abi.c file incorrectly mixes libc types
and kernel types.

> The Clang toolchain likely defaults to the traditional 32-bit time_t on
> 32-bit Debian Trixie (except x86), leading to an ABI issue similar to
> older compilers. This is affecting compatibility.
>
> This is not a new regression,
> this report generated on Linux next but also seen on Linux stable tree.
>
> Test name: kselftest-vDSO/vdso_test_abi
> Fails: gcc-13
> pass: clang-19
>
> Arnd Bergmann investigated and proposed a patch which fixes the problem.

The patch only makes changes ltp so it tests the old system calls
correctly regardless of the toolchain settings.

Someone still needs to change LTP to include this change as well as
add tests for the 64-bit time_t vdso functions.

     Arnd