libpayload/x86/exception: Add methods to enable/disable interrupts

Will be used by the APIC.

BUG=b:109749762
TEST=Verified by the other cls in the stack.

Change-Id: Id86f2719d98a90318ac625e09601e5dbb06e3765
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/28239
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

payloads/libpayload/arch/x86/exception.c

@@ -32,6 +32,8 @@
 #include <libpayload.h>
 #include <stdint.h>
 
+#define IF_FLAG				(1 << 9)
+
 u32 exception_stack[0x400] __attribute__((aligned(8)));
 
 static exception_hook hook;
@@ -182,3 +184,33 @@ void exception_install_hook(exception_hook h)
 	die_if(hook, "Implement support for a list of hooks if you need it.");
 	hook = h;
 }
+
+static uint32_t eflags(void)
+{
+	uint32_t eflags;
+	asm volatile(
+		"pushf\n\t"
+		"pop %0\n\t"
+	: "=rm" (eflags));
+	return eflags;
+}
+
+void enable_interrupts(void)
+{
+	asm volatile (
+		"sti\n"
+		: : : "cc"
+	);
+}
+void disable_interrupts(void)
+{
+	asm volatile (
+		"cli\n"
+		: : : "cc"
+	);
+}
+
+int interrupts_enabled(void)
+{
+	return !!(eflags() & IF_FLAG);
+}

payloads/libpayload/include/x86/arch/exception.h

@@ -34,6 +34,10 @@
 
 void exception_init_asm(void);
 void exception_dispatch(void);
+void enable_interrupts(void);
+void disable_interrupts(void);
+/** Returns 1 if interrupts are enabled. */
+int interrupts_enabled(void);
 
 struct exception_state
 {