[PATCH] commands: smc: disable -c (start cpu) test option for ARMv8

[Ahmad Fatoum]

This option is meant for debugging and was only tested on an ARMv7 CPU.
On ARMv8, the handshake times out and the code executing on the second
CPU invokes undefined behavior by modifying the stack base from a non-
naked function. This led so far to a warning, which went unnoticed, but
a follow-up commit will make it an error to use arm_setup_stack on
ARM64. Prepare for this by disabling -c usage on ARM64.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
Please reorder before "ARM: document arm_setup_stack() pitfalls"
---
 commands/smc.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/commands/smc.c b/commands/smc.c
index 2a53e1b64752..31430655829a 100644
--- a/commands/smc.c
+++ b/commands/smc.c
@@ -9,14 +9,15 @@
 
 #include <asm/psci.h>
 #include <asm/secure.h>
+#include <asm/barebox-arm.h>
 #include <linux/arm-smccc.h>
 
-#define STACK_SIZE 100
+#define HANDSHAKE_STACK_SIZE 100
 #define HANDSHAKE_MAGIC	0xBA12EB0C
 #define ERROR_MAGIC	0xDEADBEEF
 
 struct cpu_context {
-	unsigned long stack[STACK_SIZE];
+	unsigned long stack[HANDSHAKE_STACK_SIZE];
 	long handshake;
 };
 
@@ -35,12 +36,12 @@ static void noinline cpu_handshake(long *handshake)
 		;
 }
 
-static void __naked second_entry(unsigned long arg0)
+static void NAKED second_entry(unsigned long arg0)
 {
 	struct cpu_context *context = (void*)arg0;
 
 	arm_cpu_lowlevel_init();
-	arm_setup_stack((unsigned long)&context->stack[STACK_SIZE]);
+	arm_setup_stack((unsigned long)&context->stack[HANDSHAKE_STACK_SIZE]);
 	barrier();
 
 	cpu_handshake(&context->handshake);
@@ -110,6 +111,11 @@ static int do_smc(int argc, char *argv[])
 			printf("found psci version %ld.%ld\n", res.a0 >> 16, res.a0 & 0xffff);
 			break;
 		case 'c':
+			if (IS_ENABLED(CONFIG_CPU_64)) {
+				printf("CPU bootstrap test not supported for ARMv8\n");
+				return COMMAND_ERROR;
+			}
+
 			if (!context)
 				context = dma_alloc_coherent(sizeof(*context),
 							     DMA_ADDRESS_BROKEN);
-- 
2.30.2