[RFC PATCH 3/4] powerpc: Optimize register usage for dear register

[sxwjean at me.com]

From: Xiongwei Song <sxwjean at gmail.com>

Create an anonymous union for dar and dear regsiters, we can reference
dear to get the effective address when CONFIG_4xx=y or CONFIG_BOOKE=y.
Otherwise, reference dar. This makes code more clear.

Signed-off-by: Xiongwei Song <sxwjean at gmail.com>
---
 arch/powerpc/include/asm/ptrace.h      | 5 ++++-
 arch/powerpc/include/uapi/asm/ptrace.h | 5 ++++-
 arch/powerpc/kernel/process.c          | 2 +-
 arch/powerpc/kernel/ptrace/ptrace.c    | 2 ++
 arch/powerpc/kernel/traps.c            | 5 ++++-
 arch/powerpc/mm/fault.c                | 2 +-
 6 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index c252d04b1206..fa725e3238c2 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -43,7 +43,10 @@ struct pt_regs
 			unsigned long mq;
 #endif
 			unsigned long trap;
-			unsigned long dar;
+			union {
+				unsigned long dar;
+				unsigned long dear;
+			};
 			union {
 				unsigned long dsisr;
 				unsigned long esr;
diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
index e357288b5f34..9ae150fb4c4b 100644
--- a/arch/powerpc/include/uapi/asm/ptrace.h
+++ b/arch/powerpc/include/uapi/asm/ptrace.h
@@ -52,7 +52,10 @@ struct pt_regs
 	unsigned long trap;		/* Reason for being here */
 	/* N.B. for critical exceptions on 4xx, the dar and dsisr
 	   fields are overloaded to hold srr0 and srr1. */
-	unsigned long dar;		/* Fault registers */
+	union {
+		unsigned long dar;		/* Fault registers */
+		unsigned long dear;
+	};
 	union {
 		unsigned long dsisr;		/* on Book-S used for DSISR */
 		unsigned long esr;		/* on 4xx/Book-E used for ESR */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index f74af8f9133c..50436b52c213 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1499,7 +1499,7 @@ static void __show_regs(struct pt_regs *regs)
 	    trap == INTERRUPT_DATA_STORAGE ||
 	    trap == INTERRUPT_ALIGNMENT) {
 		if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
-			pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->esr);
+			pr_cont("DEAR: "REG" ESR: "REG" ", regs->dear, regs->esr);
 		else
 			pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
 	}
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 00789ad2c4a3..969dca8b0718 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -373,6 +373,8 @@ void __init pt_regs_check(void)
 		     offsetof(struct user_pt_regs, trap));
 	BUILD_BUG_ON(offsetof(struct pt_regs, dar) !=
 		     offsetof(struct user_pt_regs, dar));
+	BUILD_BUG_ON(offsetof(struct pt_regs, dear) !=
+		     offsetof(struct user_pt_regs, dear));
 	BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=
 		     offsetof(struct user_pt_regs, dsisr));
 	BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 2164f5705a0b..0796630d3d23 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1609,7 +1609,10 @@ DEFINE_INTERRUPT_HANDLER(alignment_exception)
 	}
 bad:
 	if (user_mode(regs))
-		_exception(sig, regs, code, regs->dar);
+		if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
+			_exception(sig, regs, code, regs->dear);
+		else
+			_exception(sig, regs, code, regs->dar);
 	else
 		bad_page_fault(regs, sig);
 }
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 62953d4e7c93..3db6b39a1178 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -542,7 +542,7 @@ static __always_inline void __do_page_fault(struct pt_regs *regs)
 	long err;
 
 	if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
-		err = ___do_page_fault(regs, regs->dar, regs->esr);
+		err = ___do_page_fault(regs, regs->dear, regs->esr);
 	else
 		err = ___do_page_fault(regs, regs->dar, regs->dsisr);
 
-- 
2.30.2