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From:   "Alastair D'Silva" <alastair@au1.ibm.com>
Cc:     "Alastair D'Silva" <alastair@d-silva.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
Date:   Wed, 13 Mar 2019 14:42:06 +1100
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From: Alastair D'Silva <alastair@d-silva.org>

When building an LTO kernel, the existing code generates warnings:
    ./arch/powerpc/include/asm/paca.h:37:30: warning: register of
        ‘local_paca’ used for multiple global register variables
     register struct paca_struct *local_paca asm("r13");
                              ^
    ./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
        ‘local_paca’

This patch reworks local_paca into an inline getter & setter function,
which addresses the warning.

Generated ASM from this patch is broadly similar (addresses have
changed and the compiler uses different GPRs in some places).

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 arch/powerpc/include/asm/paca.h | 44 +++++++++++++++++++++++----------
 arch/powerpc/kernel/paca.c      |  2 +-
 2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index e843bc5d1a0f..9c9e2dea0f9b 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -34,19 +34,6 @@
 #include <asm/cpuidle.h>
 #include <asm/atomic.h>
 
-register struct paca_struct *local_paca asm("r13");
-
-#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
-extern unsigned int debug_smp_processor_id(void); /* from linux/smp.h */
-/*
- * Add standard checks that preemption cannot occur when using get_paca():
- * otherwise the paca_struct it points to may be the wrong one just after.
- */
-#define get_paca()	((void) debug_smp_processor_id(), local_paca)
-#else
-#define get_paca()	local_paca
-#endif
-
 #ifdef CONFIG_PPC_PSERIES
 #define get_lppaca()	(get_paca()->lppaca_ptr)
 #endif
@@ -266,6 +253,37 @@ struct paca_struct {
 #endif
 } ____cacheline_aligned;
 
+#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
+extern unsigned int debug_smp_processor_id(void); /* from linux/smp.h */
+#endif
+
+static inline struct paca_struct *get_paca_no_preempt_check(void)
+{
+	register struct paca_struct *paca asm("r13");
+	return paca;
+}
+
+static inline struct paca_struct *get_paca(void)
+{
+#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
+	/*
+	 * Add standard checks that preemption cannot occur when using get_paca():
+	 * otherwise the paca_struct it points to may be the wrong one just after.
+	 */
+	debug_smp_processor_id();
+#endif
+	return get_paca_no_preempt_check();
+}
+
+#define local_paca	get_paca_no_preempt_check()
+
+static inline void set_paca(struct paca_struct *new)
+{
+	register struct paca_struct *paca asm("r13");
+	paca = new;
+}
+
+
 extern void copy_mm_to_paca(struct mm_struct *mm);
 extern struct paca_struct **paca_ptrs;
 extern void initialise_paca(struct paca_struct *new_paca, int cpu);
diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index 913bfca09c4f..ae5c243f9d5a 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -172,7 +172,7 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
 void setup_paca(struct paca_struct *new_paca)
 {
 	/* Setup r13 */
-	local_paca = new_paca;
+	set_paca(new_paca);
 
 #ifdef CONFIG_PPC_BOOK3E
 	/* On Book3E, initialize the TLB miss exception frames */
-- 
2.20.1