[LTP] [PATCH v2] arch_prctl: add ARCH_GET_FS, ARCH_GET_GS tests

[dm.chestnykh@gmail.com]

From: Dmitry Chestnykh <dm.chestnykh@gmail.com>

Signed-off-by: Dmitry Chestnykh <dm.chestnykh@gmail.com>
---
 configure.ac                                  |  1 +
 include/lapi/arch_prctl.h                     |  9 ++
 runtest/syscalls                              |  1 +
 .../kernel/syscalls/arch_prctl/.gitignore     |  1 +
 .../kernel/syscalls/arch_prctl/arch_prctl02.c | 87 +++++++++++++++++++
 5 files changed, 99 insertions(+)
 create mode 100644 testcases/kernel/syscalls/arch_prctl/arch_prctl02.c

diff --git a/configure.ac b/configure.ac
index e979de0e7..9db3e06ad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -53,6 +53,7 @@ AC_CHECK_HEADERS_ONCE([ \
     aio.h \
     asm/ldt.h \
     asm/prctl.h \
+    asm/hwcap2.h \
     cpuid.h \
     emmintrin.h \
     ifaddrs.h \
diff --git a/include/lapi/arch_prctl.h b/include/lapi/arch_prctl.h
index a4e7f8458..6d8376e58 100644
--- a/include/lapi/arch_prctl.h
+++ b/include/lapi/arch_prctl.h
@@ -19,4 +19,13 @@
 # define ARCH_SET_CPUID 0x1012
 #endif

+#ifdef __x86_64__
+# ifdef HAVE_ASM_HWCAP2_H
+#  include <asm/hwcap2.h>
+# endif /* HAVE_ASM_HWCAP2_H */
+# ifndef HWCAP2_FSGSBASE
+#  define HWCAP2_FSGSBASE (1UL << 1)
+# endif /* HWCAP2_FSGSBASE */
+#endif /* __x86_64__ */
+
 #endif /* LAPI_ARCH_PRCTL_H__ */
diff --git a/runtest/syscalls b/runtest/syscalls
index accdf2df9..f2f2a0602 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -32,6 +32,7 @@ alarm06 alarm06
 alarm07 alarm07

 arch_prctl01 arch_prctl01
+arch_prctl02 arch_prctl02

 bind01 bind01
 bind02 bind02
diff --git a/testcases/kernel/syscalls/arch_prctl/.gitignore b/testcases/kernel/syscalls/arch_prctl/.gitignore
index 24871e249..72187b8b4 100644
--- a/testcases/kernel/syscalls/arch_prctl/.gitignore
+++ b/testcases/kernel/syscalls/arch_prctl/.gitignore
@@ -1 +1,2 @@
 /arch_prctl01
+/arch_prctl02
diff --git a/testcases/kernel/syscalls/arch_prctl/arch_prctl02.c b/testcases/kernel/syscalls/arch_prctl/arch_prctl02.c
new file mode 100644
index 000000000..180c64b27
--- /dev/null
+++ b/testcases/kernel/syscalls/arch_prctl/arch_prctl02.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Dmitry Chestnykh <dm.chestnykh@gmail.com>
+ * Author: Dmitry Chestnykh <dm.chestnykh@gmail.com>
+ */
+
+/*\
+ *  Simple test on arch_prctl to get FS_BASE and GS_BASE
+ */
+
+#include "tst_test.h"
+#include "lapi/syscalls.h"
+#include "lapi/arch_prctl.h"
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef __x86_64__
+
+#ifdef HAVE_GETAUXVAL
+# include <sys/auxv.h>
+#endif
+
+static int arch_prctl_get(int code, unsigned long *out)
+{
+	return tst_syscall(__NR_arch_prctl, code, out);
+}
+
+static bool tag;
+
+static void setup(void)
+{
+    unsigned long v = 0;
+
+#ifdef AT_HWCAP2
+	v = getauxval(AT_HWCAP2);
+#endif
+	tag = v & HWCAP2_FSGSBASE ? true : false;
+}
+
+#define READ_FS_BASE() ({                              \
+	unsigned long long __res;                          \
+	asm volatile("rdfsbase %0" : "=r"(__res));         \
+	__res;                                             \
+})
+
+#define READ_GS_BASE() ({                              \
+	unsigned long long __res;                          \
+	asm volatile("rdgsbase %0" : "=r"(__res));         \
+	__res;                                             \
+})
+
+static void run(unsigned int index)
+{
+	(void)index;
+	if (!tag)
+		tst_brk(TCONF, "rdfsbase/rdgsbase are not supported/enabled");
+
+	unsigned long fs = READ_FS_BASE();
+	unsigned long gs = READ_GS_BASE();
+	unsigned long fs_prctl, gs_prctl;
+
+	TST_EXP_PASS_SILENT(arch_prctl_get(ARCH_GET_FS, &fs_prctl));
+	if (TST_PASS)
+		TST_EXP_EQ_LU(fs_prctl, fs);
+	else
+		tst_res(TFAIL, "got wrong fs register value");
+
+	TST_EXP_PASS_SILENT(arch_prctl_get(ARCH_GET_GS, &gs_prctl));
+	if (TST_PASS)
+		TST_EXP_EQ_LU(gs_prctl, gs);
+	else
+		tst_res(TFAIL, "got wrong gs register value");
+}
+
+static struct tst_test test = {
+	.test = run,
+	.setup = setup,
+	.tcnt = 1,
+	.min_kver = "5.9",
+	.supported_archs = (const char *const []){"x86_64", NULL}
+};
+
+#else
+
+TST_TEST_TCONF("Tests needs x86_64 CPU");
+
+#endif /* __x86_64__ */
--
2.56.0