x86/idtentry: Provide macros to define/declare IDT entry points

Provide DECLARE/DEFINE_IDTENTRY() macros.

DEFINE_IDTENTRY() provides a wrapper which acts as the function
definition. The exception handler body is just appended to it with curly
brackets. The entry point is marked noinstr so that irq tracing and the
enter_from_user_mode() can be moved into the C-entry point. As all
C-entries use the same macro (or a later variant) the necessary entry
handling can be implemented at one central place.

DECLARE_IDTENTRY() provides the function prototypes:
  - The C entry point 	    	cfunc
  - The ASM entry point		asm_cfunc
  - The XEN/PV entry point	xen_asm_cfunc

They all follow the same naming convention.

When included from ASM code DECLARE_IDTENTRY() is a macro which emits the
low level entry point in assembly by instantiating idtentry.

IDTENTRY is the simplest variant which just has a pt_regs argument. It's
going to be used for all exceptions which have no error code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134904.273363275@linutronix.de

arch/x86/entry/entry_32.S

@@ -752,6 +752,12 @@ SYM_CODE_START(\asmsym)
 SYM_CODE_END(\asmsym)
 .endm
 
+/*
+ * Include the defines which emit the idt entries which are shared
+ * shared between 32 and 64 bit.
+ */
+#include <asm/idtentry.h>
+
 /*
  * %eax: prev task
  * %edx: next task

arch/x86/entry/entry_64.S

@@ -698,6 +698,12 @@ _ASM_NOKPROBE(\asmsym)
 SYM_CODE_END(\asmsym)
 .endm
 
+/*
+ * Include the defines which emit the idt entries which are shared
+ * shared between 32 and 64 bit.
+ */
+#include <asm/idtentry.h>
+
 /*
  * Interrupt entry helper function.
  *

arch/x86/include/asm/idtentry.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_IDTENTRY_H
+#define _ASM_X86_IDTENTRY_H
+
+/* Interrupts/Exceptions */
+#include <asm/trapnr.h>
+
+#ifndef __ASSEMBLY__
+
+/**
+ * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
+ *		      No error code pushed by hardware
+ * @vector:	Vector number (ignored for C)
+ * @func:	Function name of the entry point
+ *
+ * Declares three functions:
+ * - The ASM entry point: asm_##func
+ * - The XEN PV trap entry point: xen_##func (maybe unused)
+ * - The C handler called from the ASM entry point
+ *
+ * Note: This is the C variant of DECLARE_IDTENTRY(). As the name says it
+ * declares the entry points for usage in C code. There is an ASM variant
+ * as well which is used to emit the entry stubs in entry_32/64.S.
+ */
+#define DECLARE_IDTENTRY(vector, func)					\
+	asmlinkage void asm_##func(void);				\
+	asmlinkage void xen_asm_##func(void);				\
+	__visible void func(struct pt_regs *regs)
+
+/**
+ * DEFINE_IDTENTRY - Emit code for simple IDT entry points
+ * @func:	Function name of the entry point
+ *
+ * @func is called from ASM entry code with interrupts disabled.
+ *
+ * The macro is written so it acts as function definition. Append the
+ * body with a pair of curly brackets.
+ *
+ * idtentry_enter() contains common code which has to be invoked before
+ * arbitrary code in the body. idtentry_exit() contains common code
+ * which has to run before returning to the low level assembly code.
+ */
+#define DEFINE_IDTENTRY(func)						\
+static __always_inline void __##func(struct pt_regs *regs);		\
+									\
+__visible noinstr void func(struct pt_regs *regs)			\
+{									\
+	idtentry_enter(regs);						\
+	instrumentation_begin();					\
+	__##func (regs);						\
+	instrumentation_end();						\
+	idtentry_exit(regs);						\
+}									\
+									\
+static __always_inline void __##func(struct pt_regs *regs)
+
+#else /* !__ASSEMBLY__ */
+
+/*
+ * The ASM variants for DECLARE_IDTENTRY*() which emit the ASM entry stubs.
+ */
+#define DECLARE_IDTENTRY(vector, func)					\
+	idtentry vector asm_##func func has_error_code=0 sane=1
+
+#endif /* __ASSEMBLY__ */
+
+#endif

arch/x86/include/asm/traps.h

@@ -6,8 +6,8 @@
 #include <linux/kprobes.h>
 
 #include <asm/debugreg.h>
+#include <asm/idtentry.h>
 #include <asm/siginfo.h>			/* TRAP_TRACE, ... */
-#include <asm/trapnr.h>
 
 #define dotraplinkage __visible