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Subject[PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
Date
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
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