[PATCH] x86, traps: early_trap_init() cleanup.

[Wang Nan <wangnan0@huawei.com>]

As early_trap_init() doesn't use IST, replace set_intr_gate_ist(..., 0)
and set_system_intr_gate_ist(..., 0) with their standard counterparts.

set_intr_gate() requires a trace_debug symbol which we don't have and
won't use. Use a small macro trick as a workaround.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---

Hi Andy Lutomirski,

   This patch is a bit tricky, but I think we don't need to define another
   helper for such a small problem. What's your opinion?

Thank you!

---
 arch/x86/kernel/traps.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4281988..c24434a 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -925,17 +925,22 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 /* Set of traps needed for early debugging. */
 void __init early_trap_init(void)
 {
+
 	/*
-	 * Don't set ist to DEBUG_STACK as it doesn't work until TSS is
-	 * ready in cpu_init() <-- trap_init(). Before trap_init(), CPU
-	 * runs at ring 0 so it is impossible to hit an invalid stack.
-	 * Using the original stack works well enough at this early
-	 * stage. DEBUG_STACK will be equipped after cpu_init() in
-	 * trap_init().
+	 * Don't use IST to set DEBUG_STACK as it doesn't work until TSS is
+	 * ready in cpu_init() <-- trap_init(). Before trap_init(), CPU runs at
+	 * ring 0 so it is impossible to hit an invalid stack.  Using the
+	 * original stack works well enough at this early stage. DEBUG_STACK
+	 * will be equipped after cpu_init() in trap_init().
+	 *
+	 * Since set_intr_gate() needs a trace_debug but we don't have it,
+	 * use the following #define as a workaround.
 	 */
-	set_intr_gate_ist(X86_TRAP_DB, &debug, 0);
+#define trace_debug debug
+	set_intr_gate(X86_TRAP_DB, debug);
+#undef trace_debug
 	/* int3 can be called from all */
-	set_system_intr_gate_ist(X86_TRAP_BP, &int3, 0);
+	set_system_intr_gate(X86_TRAP_BP, &int3);
 #ifdef CONFIG_X86_32
 	set_intr_gate(X86_TRAP_PF, page_fault);
 #endif
@@ -1015,7 +1020,7 @@ void __init trap_init(void)
 
 	/*
 	 * X86_TRAP_DB and X86_TRAP_BP have been set
-	 * in early_trap_init(). However, DEBUG_STACK works only after
+	 * in early_trap_init(). However, ITS works only after
 	 * cpu_init() loads TSS. See comments in early_trap_init().
 	 */
 	set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK);
-- 
1.8.4