Re: [LTP] arch_prctl: add ARCH_GET_FS, ARCH_GET_GS tests

[linuxtestproject.agent@gmail.com]

Hi Dmitry,

On 2026-10-09, 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
> +static int arch_prctl_get(int code, unsigned long *out)
> +{
> +	return tst_syscall(__NR_arch_prctl, code, out);
> +}

High: On x32, unsigned long is four bytes, but these raw GET operations
write eight bytes, overflowing fs_prctl and gs_prctl. Both __x86_64__ and
the framework's x86_64 architecture check admit x32; glibc's x32
arch_prctl wrapper uses a uint64_t temporary, but tst_syscall bypasses it.
Use uint64_t for the output pointer, both output objects, and comparison
values.

> +	if (gs == 0) {
> +		unsigned long test_gs = 0xabababab;
> +		TST_EXP_PASS_SILENT(set_gs(test_gs));
> +		if (TST_PASS) {
> +			TEST_GS_BASE();
> +		}
> +	}

Low: GS remains nonzero after the first iteration, so subsequent -i
iterations skip the zero-base comparison and ARCH_SET_GS branch; -i 3
produces seven comparisons rather than repeating all three each time.
Restore the original GS base after the changed-base comparison.

> +	unsigned long long __res_fs;                       \
> +	unsigned long long __res_gs;                       \
> +		if (TST_PASS) {
> +			TEST_GS_BASE();
> +		}
> +	unsigned idx;
> +static void run(unsigned index)

Low: check-arch_prctl02 reports missing blank lines after declarations,
unnecessary single-statement braces, an unnecessary blank line before a
closing brace, and bare unsigned declarations; fix these and use unsigned
int. Rename __res_fs and __res_gs to avoid reserved identifiers.

Verdict - Needs revision

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