[patch part-III V2 06/23] x86/idtentry: Provide macros to define/declare IDT entry points

[Thomas Gleixner]

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 notrace/noprobe 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@xxxxxxxxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
V2: Add comments to explain the C vs. ASM variants
---
 arch/x86/entry/entry_32.S       |    6 ++
 arch/x86/entry/entry_64.S       |    6 ++
 arch/x86/include/asm/idtentry.h |   85 ++++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/traps.h    |    2 
 4 files changed, 98 insertions(+), 1 deletion(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -769,6 +769,12 @@ 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
  */
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -688,6 +688,12 @@ 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.
  *
  * Entry runs with interrupts off. Stack layout at entry:
--- /dev/null
+++ b/arch/x86/include/asm/idtentry.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_IDTENTRY_H
+#define _ASM_X86_IDTENTRY_H
+
+/* Interrupts/Exceptions */
+#include <asm/trapnr.h>
+
+#ifndef __ASSEMBLY__
+
+/**
+ * idtentry_enter - Handle state tracking on idtentry
+ * @regs:	Pointer to pt_regs of interrupted context
+ *
+ * Place holder for now.
+ */
+static __always_inline void idtentry_enter(struct pt_regs *regs)
+{
+}
+
+/**
+ * idtentry_exit - Prepare returning to low level ASM code
+ *
+ * Place holder for now.
+ */
+static __always_inline void idtentry_exit(struct pt_regs *regs)
+{
+}
+
+/**
+ * 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 notrace void func(struct pt_regs *regs)			\
+{									\
+	idtentry_enter(regs);						\
+	__##func (regs);						\
+	idtentry_exit(regs);						\
+}									\
+NOKPROBE_SYMBOL(func);							\
+									\
+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
+
+#endif /* __ASSEMBLY__ */
+
+#endif
--- a/arch/x86/include/asm/traps.h
+++ b/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