aarch64: userspace: Implement syscalls

This patch adds the code managing the syscalls. The privileged stack
is setup before jumping into the real syscall.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

arch/arm/core/aarch64/Kconfig

@@ -64,6 +64,9 @@ config AARCH64_IMAGE_HEADER
 	  This option enables standard ARM64 boot image header used by Linux
 	  and understood by loaders such as u-boot on Xen xl tool.
 
+config PRIVILEGED_STACK_SIZE
+	default 4096
+
 if CPU_CORTEX_A
 
 config ARMV8_A_NS

arch/arm/core/aarch64/switch.S

@@ -111,6 +111,11 @@ SECTION_FUNC(TEXT, z_arm64_sync_exc)
 	cmp	x1, #_SVC_CALL_RUNTIME_EXCEPT
 	beq	oops
 
+#ifdef CONFIG_USERSPACE
+	cmp	x1, #_SVC_CALL_SYSTEM_CALL
+	beq	z_arm64_do_syscall
+#endif
+
 #ifdef CONFIG_IRQ_OFFLOAD
 	cmp	x1, #_SVC_CALL_IRQ_OFFLOAD
 	beq	offload

arch/arm/core/aarch64/thread.c

@@ -54,6 +54,7 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 	}
 
 	pInitCtx->tpidrro_el0 = 0x0;
+	thread->arch.priv_stack_start = 0;
 #else
 	pInitCtx->elr = (uint64_t)z_thread_entry;
 #endif
@@ -82,6 +83,9 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
 	z_arch_esf_t *pInitCtx;
 	uintptr_t stack_ptr;
 
+	/* Setup the private stack */
+	_current->arch.priv_stack_start = (uint64_t)(_current->stack_obj);
+
 	/* Reset the stack pointer to the base discarding any old context */
 	stack_ptr = Z_STACK_PTR_ALIGN(_current->stack_info.start +
 				      _current->stack_info.size -

arch/arm/core/aarch64/userspace.S

@@ -85,6 +85,61 @@ abv_fail:
 	mov	x0, #-1
 	ret
 
+/*
+ * System call entry point.
+ */
+
+GTEXT(z_arm64_do_syscall)
+SECTION_FUNC(TEXT, z_arm64_do_syscall)
+	/* Recover the syscall parameters from the ESF */
+	ldp	x0, x1, [sp, ___esf_t_x0_x1_OFFSET]
+	ldp	x2, x3, [sp, ___esf_t_x2_x3_OFFSET]
+	ldp	x4, x5, [sp, ___esf_t_x4_x5_OFFSET]
+
+	/* Recover the syscall ID */
+	ldr	x8, [sp, ___esf_t_x8_x9_OFFSET]
+
+	/* Check whether the ID is valid */
+	ldr	x9, =K_SYSCALL_LIMIT
+	cmp	x8, x9
+	blo	valid_syscall_id
+	ldr	x8, =K_SYSCALL_BAD
+
+valid_syscall_id:
+	ldr	x9, =_k_syscall_table
+	ldr	x9, [x9, x8, lsl #3]
+
+	/* Recover the privileged stack */
+#ifdef CONFIG_SMP
+	get_cpu	x10, x8
+	ldr	x10, [x10, #___cpu_t_current_OFFSET]
+#else
+	ldr	x10, =_kernel
+	ldr	x10, [x10, #_kernel_offset_to_current]
+#endif
+	ldr     x10, [x10, #_thread_offset_to_priv_stack_start]
+	add	x10, x10, #CONFIG_PRIVILEGED_STACK_SIZE
+
+	/* Save the original SP on the privileged stack */
+	mov	x11, sp
+	mov	sp, x10
+	str	x11,  [sp, #-16]!
+
+	/* Jump into the syscall */
+	msr	daifclr, #(DAIFSET_IRQ_BIT)
+	blr	x9
+	msr	daifset, #(DAIFSET_IRQ_BIT)
+
+	/* Restore the original SP containing the ESF */
+	ldr	x11, [sp], #16
+	mov	sp, x11
+
+	/* Save the return value into the ESF */
+	str	x0, [sp, ___esf_t_x0_x1_OFFSET]
+
+	/* Return from exception */
+	b	z_arm64_exit_exc
+
 /*
  * Routine to jump into userspace
  *

arch/arm/core/offsets/offsets_aarch64.c

@@ -29,6 +29,10 @@
 #include <kernel_arch_data.h>
 #include <kernel_offsets.h>
 
+#ifdef CONFIG_USERSPACE
+GEN_OFFSET_SYM(_thread_arch_t, priv_stack_start);
+#endif
+
 GEN_NAMED_OFFSET_SYM(_callee_saved_t, x19, x19_x20);
 GEN_NAMED_OFFSET_SYM(_callee_saved_t, x21, x21_x22);
 GEN_NAMED_OFFSET_SYM(_callee_saved_t, x23, x23_x24);

arch/arm/include/aarch64/offsets_short_arch.h

@@ -9,4 +9,9 @@
 
 #include <offsets.h>
 
+#ifdef CONFIG_USERSPACE
+#define _thread_offset_to_priv_stack_start \
+	(___thread_t_arch_OFFSET + ___thread_arch_t_priv_stack_start_OFFSET)
+#endif
+
 #endif /* ZEPHYR_ARCH_ARM_INCLUDE_AARCH64_OFFSETS_SHORT_ARCH_H_ */

include/arch/arm/aarch64/syscall.h

@@ -19,6 +19,7 @@
 #define _SVC_CALL_CONTEXT_SWITCH	0
 #define _SVC_CALL_IRQ_OFFLOAD		1
 #define _SVC_CALL_RUNTIME_EXCEPT	2
+#define _SVC_CALL_SYSTEM_CALL		3
 
 #ifdef CONFIG_USERSPACE
 #ifndef _ASMLANGUAGE
@@ -31,6 +32,137 @@
 extern "C" {
 #endif
 
+/*
+ * Syscall invocation macros. arm-specific machine constraints used to ensure
+ * args land in the proper registers.
+ */
+static inline uintptr_t arch_syscall_invoke6(uintptr_t arg1, uintptr_t arg2,
+					     uintptr_t arg3, uintptr_t arg4,
+					     uintptr_t arg5, uintptr_t arg6,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r1 __asm__("x1") = arg2;
+	register uint64_t r2 __asm__("x2") = arg3;
+	register uint64_t r3 __asm__("x3") = arg4;
+	register uint64_t r4 __asm__("x4") = arg5;
+	register uint64_t r5 __asm__("x5") = arg6;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r1), "r" (r2), "r" (r3),
+			   "r" (r4), "r" (r5), "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke5(uintptr_t arg1, uintptr_t arg2,
+					     uintptr_t arg3, uintptr_t arg4,
+					     uintptr_t arg5,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r1 __asm__("x1") = arg2;
+	register uint64_t r2 __asm__("x2") = arg3;
+	register uint64_t r3 __asm__("x3") = arg4;
+	register uint64_t r4 __asm__("x4") = arg5;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r1), "r" (r2), "r" (r3),
+			   "r" (r4), "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke4(uintptr_t arg1, uintptr_t arg2,
+					     uintptr_t arg3, uintptr_t arg4,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r1 __asm__("x1") = arg2;
+	register uint64_t r2 __asm__("x2") = arg3;
+	register uint64_t r3 __asm__("x3") = arg4;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r1), "r" (r2), "r" (r3),
+			   "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke3(uintptr_t arg1, uintptr_t arg2,
+					     uintptr_t arg3,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r1 __asm__("x1") = arg2;
+	register uint64_t r2 __asm__("x2") = arg3;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r1), "r" (r2), "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke2(uintptr_t arg1, uintptr_t arg2,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r1 __asm__("x1") = arg2;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r1), "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke1(uintptr_t arg1,
+					     uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0") = arg1;
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r8)
+			 : "memory");
+	return ret;
+}
+
+static inline uintptr_t arch_syscall_invoke0(uintptr_t call_id)
+{
+	register uint64_t ret __asm__("x0");
+	register uint64_t r8 __asm__("x8") = call_id;
+
+	__asm__ volatile("svc %[svid]\n"
+			 : "=r"(ret)
+			 : [svid] "i" (_SVC_CALL_SYSTEM_CALL),
+			   "r" (ret), "r" (r8)
+			 : "memory");
+
+	return ret;
+}
+
 static inline bool arch_is_user_context(void)
 {
 	uint64_t tpidrro_el0;

include/arch/arm/aarch64/thread.h

@@ -40,7 +40,9 @@ struct _callee_saved {
 typedef struct _callee_saved _callee_saved_t;
 
 struct _thread_arch {
-	/* empty */
+#ifdef CONFIG_USERSPACE
+	uint64_t priv_stack_start;
+#endif
 };
 
 typedef struct _thread_arch _thread_arch_t;