[PATCH] alpha: Implement "current_stack_pointer"

[Kees Cook <keescook@chromium.org>]

To follow the existing per-arch conventions replace open-coded use
of asm "$30" as "current_stack_pointer". This will let it be used in
non-arch places (like HARDENED_USERCOPY).

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: "Alexander A. Klimov" <grandmaster@al2klimov.de>
Cc: linux-alpha@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/alpha/Kconfig                   | 1 +
 arch/alpha/include/asm/thread_info.h | 2 ++
 arch/alpha/lib/stacktrace.c          | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 4e87783c90ad..31f3dbcdc28c 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -3,6 +3,7 @@ config ALPHA
 	bool
 	default y
 	select ARCH_32BIT_USTAT_F_TINODE
+	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select ARCH_NO_PREEMPT
diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h
index 2592356e3215..28214db31053 100644
--- a/arch/alpha/include/asm/thread_info.h
+++ b/arch/alpha/include/asm/thread_info.h
@@ -43,6 +43,8 @@ struct thread_info {
 register struct thread_info *__current_thread_info __asm__("$8");
 #define current_thread_info()  __current_thread_info
 
+register unsigned long *current_stack_pointer __asm__ ("$30");
+
 #endif /* __ASSEMBLY__ */
 
 /* Thread information allocation.  */
diff --git a/arch/alpha/lib/stacktrace.c b/arch/alpha/lib/stacktrace.c
index 62454a7810e2..2b1176dd5174 100644
--- a/arch/alpha/lib/stacktrace.c
+++ b/arch/alpha/lib/stacktrace.c
@@ -92,7 +92,7 @@ stacktrace(void)
 {
 	instr * ret_pc;
 	instr * prologue = (instr *)stacktrace;
-	register unsigned char * sp __asm__ ("$30");
+	unsigned char *sp = (unsigned char *)current_stack_pointer;
 
 	printk("\tstack trace:\n");
 	do {
-- 
2.30.2