[PATCH] selftests: sigaltstack: fix -Wuninitialized

[Nick Desaulniers <ndesaulniers@google.com>]

Building sigaltstack with clang via:
$ ARCH=x86 make LLVM=1 -C tools/testing/selftests/sigaltstack/

produces the following warning:
  warning: variable 'sp' is uninitialized when used here [-Wuninitialized]
  if (sp < (unsigned long)sstack ||
      ^~

Clang expects these to be declared at global scope; we've fixed this in
the kernel proper by using the macro `current_stack_pointer`. This is
defined in different headers for different target architectures, so just
create a new header that defines the arch-specific register names for
the stack pointer register, and define it for more targets (at least the
ones that support current_stack_pointer/ARCH_HAS_CURRENT_STACK_POINTER).

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Link: https://lore.kernel.org/lkml/CA+G9fYsi3OOu7yCsMutpzKDnBMAzJBCPimBp86LhGBa0eCnEpA@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: KERNEL SELFTEST FRAMEWORK <linux-kselftest@vger.kernel.org>
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: lkft-triage@lists.linaro.org
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Stas Sergeev <stsp@list.ru>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: llvm@lists.linux.dev
---
 .../sigaltstack/current_stack_pointer.h       | 23 +++++++++++++++++++
 tools/testing/selftests/sigaltstack/sas.c     |  7 +-----
 2 files changed, 24 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/sigaltstack/current_stack_pointer.h

diff --git a/tools/testing/selftests/sigaltstack/current_stack_pointer.h b/tools/testing/selftests/sigaltstack/current_stack_pointer.h
new file mode 100644
index 000000000000..ea9bdf3a90b1
--- /dev/null
+++ b/tools/testing/selftests/sigaltstack/current_stack_pointer.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#if __alpha__
+register unsigned long sp asm("$30");
+#elif __arm__ || __aarch64__ || __csky__ || __m68k__ || __mips__ || __riscv
+register unsigned long sp asm("sp");
+#elif __i386__
+register unsigned long sp asm("esp");
+#elif __loongarch64
+register unsigned long sp asm("$sp");
+#elif __ppc__
+register unsigned long sp asm("r1");
+#elif __s390x__
+register unsigned long sp asm("%15");
+#elif __sh__
+register unsigned long sp asm("r15");
+#elif __x86_64__
+register unsigned long sp asm("rsp");
+#elif __XTENSA__
+register unsigned long sp asm("a1");
+#else
+#error "implement current_stack_pointer equivalent"
+#endif
diff --git a/tools/testing/selftests/sigaltstack/sas.c b/tools/testing/selftests/sigaltstack/sas.c
index c53b070755b6..98d37cb744fb 100644
--- a/tools/testing/selftests/sigaltstack/sas.c
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -20,6 +20,7 @@
 #include <sys/auxv.h>
 
 #include "../kselftest.h"
+#include "current_stack_pointer.h"
 
 #ifndef SS_AUTODISARM
 #define SS_AUTODISARM  (1U << 31)
@@ -46,12 +47,6 @@ void my_usr1(int sig, siginfo_t *si, void *u)
 	stack_t stk;
 	struct stk_data *p;
 
-#if __s390x__
-	register unsigned long sp asm("%15");
-#else
-	register unsigned long sp asm("sp");
-#endif
-
 	if (sp < (unsigned long)sstack ||
 			sp >= (unsigned long)sstack + stack_size) {
 		ksft_exit_fail_msg("SP is not on sigaltstack\n");
-- 
2.40.0.rc0.216.gc4246ad0f0-goog