x86: move some per-cpu initialization to C

No reason we need to stay in assembly domain once we have
GS and a stack set up.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

arch/x86/core/intel64/cpu.c

@@ -117,3 +117,28 @@ void arch_start_cpu(int cpu_num, k_thread_stack_t *stack, int sz,
 	while (x86_cpuboot[cpu_num].ready == 0) {
 	}
 }
+
+/* Per-CPU initialization, C domain. On the first CPU, z_x86_prep_c is the
+ * next step. For other CPUs it is probably smp_init_top().
+ */
+FUNC_NORETURN void z_x86_cpu_init(struct x86_cpuboot *cpuboot)
+{
+	x86_sse_init(NULL);
+
+	z_loapic_enable();
+
+#ifdef CONFIG_USERSPACE
+	/* Set landing site for 'syscall' instruction */
+	z_x86_msr_write(X86_LSTAR_MSR, (u64_t)z_x86_syscall_entry_stub);
+
+	/* Set segment descriptors for syscall privilege transitions */
+	z_x86_msr_write(X86_STAR_MSR, (u64_t)X86_STAR_UPPER << 32);
+
+	/* Mask applied to RFLAGS when making a syscall */
+	z_x86_msr_write(X86_FMASK_MSR, EFLAGS_SYSCALL);
+#endif
+
+	/* Enter kernel, never return */
+	cpuboot->ready++;
+	cpuboot->fn(cpuboot->arg);
+}

arch/x86/core/intel64/locore.S

@@ -162,42 +162,9 @@ go64:	movl %cr4, %eax			/* enable PAE and SSE */
 	rep stosq
 #endif
 
-	xorl %edi, %edi
-	call x86_sse_init
-
-#ifdef CONFIG_LOAPIC
-	call z_loapic_enable
-#endif
-
-#ifdef CONFIG_USERSPACE
-	/* Set landing site for system calls made with 'syscall' instruction */
-	movq $z_x86_syscall_entry_stub, %rax
-	movq %rax, %rdx
-	shrq $32, %rdx
-	movl $X86_LSTAR_MSR, %ecx
-	/* LSTAR set to 64-bit address denoted by EDX:EAX */
-	wrmsr
-
-	/* Set segment descriptors in STAR */
-	xorl %eax, %eax			/* Zero low bits, reserved */
-	movl $X86_STAR_UPPER, %edx
-	movl $X86_STAR_MSR, %ecx
-	wrmsr
-
-	/* Set EFLAGS mask applied when making system calls. Currently we
-	 * mask interrupts and clear direction flag.
-	 */
-	movl $0x600, %eax
-	xorl %edx, %edx
-	movl $X86_FMASK_MSR, %ecx
-	wrmsr
-#endif /* CONFIG_USERSPACE */
-
-	/* don't replace CALL with JMP; honor the ABI stack alignment! */
-
-	incl __x86_cpuboot_t_ready_OFFSET(%rbp)
-	movq __x86_cpuboot_t_arg_OFFSET(%rbp), %rdi
-	call *__x86_cpuboot_t_fn_OFFSET(%rbp) /* enter kernel; never return */
+	/* Enter C domain now that we have a stack set up, never to return */
+	movq %rbp, %rdi
+	call z_x86_cpu_init
 
 /*
  * void x86_sse_init(struct k_thread *thread);

arch/x86/include/intel64/kernel_arch_func.h

@@ -30,6 +30,12 @@ static inline void arch_kernel_init(void)
 	/* nothing */;
 }
 
+FUNC_NORETURN void z_x86_cpu_init(struct x86_cpuboot *cpuboot);
+
+void x86_sse_init(struct k_thread *thread);
+
+void z_x86_syscall_entry_stub(void);
+
 #endif /* _ASMLANGUAGE */
 
 #endif /* ZEPHYR_ARCH_X86_INCLUDE_INTEL64_KERNEL_ARCH_FUNC_H_ */

arch/x86/include/kernel_arch_data.h

@@ -41,9 +41,11 @@
  * EFLAGS/RFLAGS definitions. (RFLAGS is just zero-extended EFLAGS.)
  */
 
-#define EFLAGS_IF	0x00000200U	/* interrupts enabled */
-#define EFLAGS_INITIAL	(EFLAGS_IF)
+#define EFLAGS_IF	BIT(9)	/* interrupts enabled */
+#define EFLAGS_DF	BIT(10)	/* Direction flag */
 
+#define EFLAGS_INITIAL	(EFLAGS_IF)
+#define EFLAGS_SYSCALL	(EFLAGS_IF | EFLAGS_DF)
 /*
  * Control register definitions.
  */