[LTP] arch_prctl: add ARCH_GET_FS, ARCH_GET_GS tests

[linuxtestproject.agent@gmail.com]

Hi Dmitry,

On Sat, 10 Oct 2026, Dmitry Chestnykh wrote:
> arch_prctl: add ARCH_GET_FS, ARCH_GET_GS tests

> diff --git a/testcases/kernel/syscalls/arch_prctl/arch_prctl02.c b/testcases/kernel/syscalls/arch_prctl/arch_prctl02.c
> +	if (gs == 0) {
> +		unsigned long long test_gs = 0xabababab;

Medium: Both exercised GS bases fit in 32 bits when the initial base is
zero, so an ARCH_GET_GS implementation that drops the upper 32 bits still
passes. Include a valid base above UINT32_MAX, such as 0x1ababababULL, to
exercise the documented 64-bit result.

> +		set_gs(orig_gs);

Medium: The restoration syscall's return value is discarded. Injecting
EPERM here leaves GS nonzero, but -i 3 exits successfully with seven
passes and silently skips the set/read case in subsequent iterations.
Use TST_EXP_PASS_SILENT(set_gs(orig_gs)) and abort with TBROK on failure.

Verdict - Needs revision

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