[PATCH] tiny: Make x86 doublefault handling optional

This adds configurable support for doublefault reporting on x86

add/remove: 0/3 grow/shrink: 0/1 up/down: 0/-13048 (-13048)
function old new delta
cpu_init 846 786 -60
doublefault_fn 188 - -188
doublefault_stack 4096 - -4096
doublefault_tss 8704 - -8704

Signed-off-by: Matt Mackall <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/Makefile

···
 obj-y	:= process.o semaphore.o signal.o entry.o traps.o irq.o vm86.o \
 		ptrace.o time.o ioport.o ldt.o setup.o i8259.o sys_i386.o \
 		pci-dma.o i386_ksyms.o i387.o dmi_scan.o bootflag.o \
-		doublefault.o quirks.o i8237.o
+		quirks.o i8237.o
 
 obj-y				+= cpu/
 obj-y				+= timers/
···
 obj-$(CONFIG_ACPI_SRAT) 	+= srat.o
 obj-$(CONFIG_HPET_TIMER) 	+= time_hpet.o
 obj-$(CONFIG_EFI) 		+= efi.o efi_stub.o
+obj-$(CONFIG_DOUBLEFAULT) 	+= doublefault.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 
 EXTRA_AFLAGS   := -traditional

arch/i386/kernel/cpu/common.c

···
 	load_TR_desc();
 	load_LDT(&init_mm.context);
 
+#ifdef CONFIG_DOUBLEFAULT
 	/* Set up doublefault TSS pointer in the GDT */
 	__set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss);
+#endif
 
 	/* Clear %fs and %gs. */
 	asm volatile ("xorl %eax, %eax; movl %eax, %fs; movl %eax, %gs");

init/Kconfig

···
           option for embedded systems with no facilities for reporting errors.
           Just say Y.
 
+config DOUBLEFAULT
+	depends X86
+	default y if X86
+	bool "Enable doublefault exception handler" if EMBEDDED
+	help
+          This option allows trapping of rare doublefault exceptions that
+          would otherwise cause a system to silently reboot. Disabling this
+          option saves about 4k.
+
 config BASE_FULL
 	default y
 	bool "Enable full-sized data structures for core" if EMBEDDED