arch/x86: CONFIG_BOOTLOADER_UNKNOWN renamed to CONFIG_X86_MULTIBOOT

The only use of the BOOTLOADER_UNKNOWN config option is on x86, where
it controls whether a multiboot header is embedded in the output.
This patch renames the option to be more descriptive, and makes it
an x86-specific option, rather than a Zephyr top-level option.

This also enables X86_MULTIBOOT by default, since the header only
occupies 12-16 bytes of memory and is (almost always) harmless.

Signed-off-by: Charles E. Youse <charles.youse@intel.com>

Kconfig.zephyr

@@ -392,15 +392,6 @@ config BOOTLOADER_KEXEC
 	  This option signifies that Linux boots the kernel using kexec system call
 	  and utility. This method is used to boot the kernel over the network.
 
-config BOOTLOADER_UNKNOWN
-	bool "Generic boot loader support"
-	depends on X86
-	help
-	  This option signifies that the target has a generic bootloader
-	  or that it supports multiple ways of booting and it isn't clear
-	  at build time which method is to be used. When this option is enabled
-	  the board may have to do extra work to ensure a proper startup.
-
 config BOOTLOADER_CONTEXT_RESTORE
 	bool "Boot loader has context restore support"
 	default y

arch/x86/Kconfig

@@ -11,6 +11,16 @@ menu "X86 Architecture Options"
 config ARCH
 	default "x86"
 
+config X86_MULTIBOOT
+	bool "Generate multiboot header"
+	default y
+	help
+	  Embed a multiboot header in the output executable. This is used
+	  by some boot loaders (e.g., GRUB) when loading Zephyr. It is safe
+	  to leave this option on if you're not sure. It only expands the
+	  text segment by 12-16 bytes and is typically ignored if not needed.
+
+
 source "arch/x86/core/Kconfig"
 
 #

arch/x86/core/crt0.S

@@ -466,7 +466,7 @@ z_x86_idt:
 	.long	_idt_base_address		/* physical start address */
 
 
-#ifdef CONFIG_BOOTLOADER_UNKNOWN
+#ifdef CONFIG_X86_MULTIBOOT
 	/* Multiboot header definition is needed for some bootloaders */
 
 	/*
@@ -495,7 +495,7 @@ z_x86_idt:
 	 */
 
 	.long	-(0x1BADB002 + 0)
-#endif /* CONFIG_BOOTLOADER_UNKNOWN */
+#endif /* CONFIG_X86_MULTIBOOT */
 
 #ifdef CONFIG_SET_GDT
 

soc/x86/apollo_lake/Kconfig.soc

@@ -7,7 +7,6 @@
 config SOC_APOLLO_LAKE
 	bool "Intel Apollo Lake Soc"
 	select CPU_APOLLO_LAKE
-	select BOOTLOADER_UNKNOWN
 	select HAS_I2C_DW
 	select PCI
 	select PCI_ENUMERATION

soc/x86/atom/Kconfig.soc

@@ -3,6 +3,5 @@
 config SOC_ATOM
 	bool "Intel ATOM SoC"
 	select CPU_ATOM
-	select BOOTLOADER_UNKNOWN
 	select X86_MMU
 	select ARCH_HAS_USERSPACE

soc/x86/ia32/Kconfig.soc

@@ -3,4 +3,3 @@
 config SOC_IA32
 	bool "Generic IA32 SoC"
 	select CPU_MINUTEIA
-	select BOOTLOADER_UNKNOWN

soc/x86/intel_quark/quark_d2000/Kconfig.defconfig.series

@@ -12,6 +12,9 @@ config SOC_SERIES
 config X86_IAMCU
         default y
 
+config X86_MULTIBOOT
+	default n
+
 config SYS_CLOCK_HW_CYCLES_PER_SEC
 	default 32000000
 

soc/x86/intel_quark/quark_se/Kconfig.defconfig.series

@@ -12,6 +12,9 @@ config SOC_SERIES
 config X86_IAMCU
 	default y
 
+config X86_MULTIBOOT
+	default n
+
 config X86_NO_MELTDOWN
 	default y
 

soc/x86/intel_quark/quark_x1000/Kconfig.series

@@ -5,7 +5,6 @@ config SOC_SERIES_QUARK_X1000
 	select CPU_MINUTEIA
 	select CPU_HAS_FPU
 	select HPET_TIMER
-	select BOOTLOADER_UNKNOWN
 	select PCI
 	select PCI_ENUMERATION
 	select PCIE

soc/x86/intel_quark/quark_x1000/Kconfig.soc

@@ -5,7 +5,6 @@ config SOC_QUARK_X1000
 	select CPU_MINUTEIA
 	select CPU_HAS_FPU
 	select HPET_TIMER
-	select BOOTLOADER_UNKNOWN
 	select PCI
 	select PCI_ENUMERATION
 	select PCIE