arch/x86: Expand cpu boot argument

In order to mitigate at runtime whether it booted on multiboot or EFI,
let's introduce a dedicated x86 cpu argument structure which holds the
type and the actual pointer delivered by the method (multiboot_info, or
efi_system_table)

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>

arch/x86/core/ia32/crt0.S

@@ -44,6 +44,8 @@
 	GDATA(_sse_mxcsr_default_value)
 #endif
 
+	GDATA(x86_cpu_boot_arg)
+
 .macro install_page_tables
 #ifdef CONFIG_X86_MMU
 	/* Enable paging. If virtual memory is enabled, the instruction pointer
@@ -269,7 +271,13 @@ __csSet:
 	/* load 32-bit operand size IDT */
 	lidt	z_x86_idt
 
-	pushl	%ebx		/* pointer to multiboot info, or NULL */
+	movl	$x86_cpu_boot_arg, %ebp
+	/* Boot type to multiboot, ebx content will help to mitigate */
+	movl	$MULTIBOOT_BOOT_TYPE, \
+			__x86_boot_arg_t_boot_type_OFFSET(%ebp)
+	/* pointer to multiboot info, or NULL */
+	movl	%ebx, __x86_boot_arg_t_arg_OFFSET(%ebp)
+	pushl	$x86_cpu_boot_arg
 	call	z_x86_prep_c	/* enter kernel; never returns */
 
 #if defined(CONFIG_X86_SSE)

arch/x86/core/intel64/cpu.c

@@ -90,6 +90,14 @@ struct x86_tss64 tss3 = {
 };
 #endif
 
+
+/* We must put this in a dedicated section, or else it will land into .bss:
+ * in this case, though locore.S initalizes it relevantly, all will be
+ * lost when calling z_bss_zero() in z_x86_cpu_init prior to using it.
+ */
+Z_GENERIC_SECTION(.boot_arg)
+x86_boot_arg_t x86_cpu_boot_arg;
+
 struct x86_cpuboot x86_cpuboot[] = {
 	{
 		.tr = X86_KERNEL_CPU0_TR,
@@ -99,6 +107,7 @@ struct x86_cpuboot x86_cpuboot[] = {
 		.stack_size =
 			Z_KERNEL_STACK_SIZE_ADJUST(CONFIG_ISR_STACK_SIZE),
 		.fn = z_x86_prep_c,
+		.arg = &x86_cpu_boot_arg,
 	},
 #if CONFIG_MP_NUM_CPUS > 1
 	{

arch/x86/core/intel64/locore.S

@@ -190,9 +190,14 @@ __start32:
 	 * has left a pointer to it in EBX.
 	 */
 
-	movl $x86_cpuboot, %ebp		/* BSP is always logical CPU id 0 */
-	movl %ebx, __x86_cpuboot_t_arg_OFFSET(%ebp)	/* multiboot info */
+	movl $x86_cpu_boot_arg, %ebp
 
+	/* Inserting boot type */
+	movl $MULTIBOOT_BOOT_TYPE, __x86_boot_arg_t_boot_type_OFFSET(%ebp)
+	/* and multiboot info */
+	movl %ebx, __x86_boot_arg_t_arg_OFFSET(%ebp)
+
+	movl $x86_cpuboot, %ebp         /* BSP is always logical CPU id 0 */
 
 go64:	/* Install page tables and transition to long mode */
 	install_pagetables_32

arch/x86/core/offsets/offsets.c

@@ -14,6 +14,9 @@
 #include "ia32_offsets.c"
 #endif
 
+GEN_OFFSET_SYM(x86_boot_arg_t, boot_type);
+GEN_OFFSET_SYM(x86_boot_arg_t, arg);
+
 GEN_OFFSET_SYM(_thread_arch_t, flags);
 
 GEN_ABS_SYM_END

arch/x86/core/prep_c.c

@@ -13,13 +13,17 @@
 extern FUNC_NORETURN void z_cstart(void);
 extern void x86_64_irq_init(void);
 
+#if !defined(CONFIG_X86_64)
+x86_boot_arg_t x86_cpu_boot_arg;
+#endif
+
 /* Early global initialization functions, C domain. This runs only on the first
  * CPU for SMP systems.
  */
 __boot_func
 FUNC_NORETURN void z_x86_prep_c(void *arg)
 {
-	struct multiboot_info *info = arg;
+	x86_boot_arg_t *cpu_arg = arg;
 
 	_kernel.cpus[0].nested = 0;
 
@@ -39,11 +43,13 @@ FUNC_NORETURN void z_x86_prep_c(void *arg)
 	x86_64_irq_init();
 #endif
 
-#if defined(CONFIG_MULTIBOOT_INFO) && !defined(CONFIG_BUILD_OUTPUT_EFI)
-	z_multiboot_init(info);
-#else
-	ARG_UNUSED(info);
-#endif
+
+if (IS_ENABLED(CONFIG_MULTIBOOT_INFO) &&
+    cpu_arg->boot_type == MULTIBOOT_BOOT_TYPE) {
+	z_multiboot_init((struct multiboot_info *)cpu_arg->arg);
+} else {
+	ARG_UNUSED(cpu_arg);
+}
 
 #if CONFIG_X86_STACK_PROTECTION
 	for (int i = 0; i < CONFIG_MP_NUM_CPUS; i++) {

arch/x86/include/kernel_arch_data.h

@@ -57,6 +57,18 @@
 #define CR4_PAE		BIT(5)		/* enable PAE */
 #define CR4_OSFXSR	BIT(9)		/* enable SSE (OS FXSAVE/RSTOR) */
 
+#ifndef _ASMLANGUAGE
+
+/* x86 boot argument (see prep_c.c) */
+struct x86_boot_arg {
+	int boot_type;
+	void *arg;
+};
+
+typedef struct x86_boot_arg x86_boot_arg_t;
+
+#endif /* _ASMLANGUAGE  */
+
 #ifdef CONFIG_X86_64
 #include <intel64/kernel_arch_data.h>
 #else

include/arch/x86/intel64/linker.ld

@@ -60,6 +60,7 @@ SECTIONS
 	z_shared_kernel_page_start = .;
 #endif /* CONFIG_X86_KPTI */
 
+        *(.boot_arg)
 	*(.tss)
 	*(.gdt)
 

include/arch/x86/multiboot.h

@@ -62,6 +62,9 @@ struct multiboot_mmap {
 
 #endif /* _ASMLANGUAGE */
 
+/* Boot type value (see prep_c.c) */
+#define MULTIBOOT_BOOT_TYPE 1
+
 /*
  * Possible values for multiboot_mmap.type field.
  * Other values should be assumed to be unusable ranges.