[PATCH] sparseirq: work around __weak alias bug

[Ingo Molnar]

Impact: fix boot crash if the kernel is built with certain GCC versions

GCC has a bug with __weak alias functions: if the functions are in
the same compilation unit as their call site, GCC can decide to
inline them - and thus rob the linker of the opportunity to override
the weak alias with the real thing.

This can lead to the boot crash reported by Kamalesh Babulal:

 ACPI: Core revision 20080926
 Setting APIC routing to flat
 BUG: unable to handle kernel NULL pointer dereference at
 0000000000000000
 IP: [<ffffffff8021f9a8>] add_pin_to_irq_cpu+0x14/0x74
 PGD 0
 Oops: 0000 [#1] SMP
 [...]

So move the arch_init_chip_data() function from handle.c to manage.c.

Reported-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/irq/handle.c |    5 -----
 kernel/irq/manage.c |    9 +++++++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 157c04c..c20db0b 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -86,11 +86,6 @@ void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr)
 		desc->kstat_irqs = (unsigned int *)ptr;
 }
 
-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)
 {
 	memcpy(desc, &irq_desc_init, sizeof(struct irq_desc));
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 46953a0..c2741b0 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -261,6 +261,15 @@ void enable_irq(unsigned int irq)
 }
 EXPORT_SYMBOL(enable_irq);
 
+/*
+ * [ Not in kernel/irq/handle.c, so that GCC does not
+ *   inline the __weak alias: ]
+ */
+int __weak arch_init_chip_data(struct irq_desc *desc, int cpu)
+{
+	return 0;
+}
+
 static int set_irq_wake_real(unsigned int irq, unsigned int on)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
--
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