sparseirq: work around compiler optimizing away __weak functions

Impact: fix panic on null pointer with sparseirq

Some GCC versions seem to inline the weak global function,
when that function is empty.

Work it around, by making the functions return a (dummy) integer.
Signed-off-by: Yinghai <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/io_apic.c

@@ -170,7 +170,7 @@ static struct irq_cfg irq_cfgx[NR_IRQS] = {
 	[15] = { .domain = CPU_MASK_ALL, .vector = IRQ15_VECTOR, },
 };
 
-void __init arch_early_irq_init(void)
+int __init arch_early_irq_init(void)
 {
 	struct irq_cfg *cfg;
 	struct irq_desc *desc;
@@ -184,6 +184,8 @@ void __init arch_early_irq_init(void)
 		desc = irq_to_desc(i);
 		desc->chip_data = &cfg[i];
 	}
+
+	return 0;
 }
 
 #ifdef CONFIG_SPARSE_IRQ
@@ -212,7 +214,7 @@ static struct irq_cfg *get_one_free_irq_cfg(int cpu)
 	return cfg;
 }
 
-void arch_init_chip_data(struct irq_desc *desc, int cpu)
+int arch_init_chip_data(struct irq_desc *desc, int cpu)
 {
 	struct irq_cfg *cfg;
 
@@ -224,6 +226,8 @@ void arch_init_chip_data(struct irq_desc *desc, int cpu)
 			BUG_ON(1);
 		}
 	}
+
+	return 0;
 }
 
 #ifdef CONFIG_NUMA_MIGRATE_IRQ_DESC

include/linux/irq.h

@@ -193,9 +193,9 @@ struct irq_desc {
 	const char		*name;
 } ____cacheline_internodealigned_in_smp;
 
-extern void early_irq_init(void);
-extern void arch_early_irq_init(void);
-extern void arch_init_chip_data(struct irq_desc *desc, int cpu);
+extern int early_irq_init(void);
+extern int arch_early_irq_init(void);
+extern int arch_init_chip_data(struct irq_desc *desc, int cpu);
 extern void arch_init_copy_chip_data(struct irq_desc *old_desc,
 					struct irq_desc *desc, int cpu);
 extern void arch_free_chip_data(struct irq_desc *old_desc, struct irq_desc *desc);

init/main.c

@@ -539,13 +539,14 @@ void __init __weak thread_info_cache_init(void)
 {
 }
 
-void __init __weak arch_early_irq_init(void)
+int __init __weak arch_early_irq_init(void)
 {
+	return 0;
 }
 
-void __init __weak early_irq_init(void)
+int __init __weak early_irq_init(void)
 {
-	arch_early_irq_init();
+	return arch_early_irq_init();
 }
 
 asmlinkage void __init start_kernel(void)

kernel/irq/handle.c

@@ -86,8 +86,9 @@ void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr)
 		desc->kstat_irqs = (unsigned int *)ptr;
 }
 
-void __attribute__((weak)) arch_init_chip_data(struct irq_desc *desc, int cpu)
+int __weak arch_init_chip_data(struct irq_desc *desc, int cpu)
 {
+	return 0;
 }
 
 static void init_one_irq_desc(int irq, struct irq_desc *desc, int cpu)
@@ -132,7 +133,7 @@ static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_sm
 /* FIXME: use bootmem alloc ...*/
 static unsigned int kstat_irqs_legacy[NR_IRQS_LEGACY][NR_CPUS];
 
-void __init early_irq_init(void)
+int __init early_irq_init(void)
 {
 	struct irq_desc *desc;
 	int legacy_count;
@@ -151,7 +152,7 @@ void __init early_irq_init(void)
 	for (i = legacy_count; i < NR_IRQS; i++)
 		irq_desc_ptrs[i] = NULL;
 
-	arch_early_irq_init();
+	return arch_early_irq_init();
 }
 
 struct irq_desc *irq_to_desc(unsigned int irq)