cant compile on alpha with gcc-4.3 and CONFIG_ALPHA_NAUTILUS

cant compile on alpha with gcc-4.3 and CONFIG_ALPHA_NAUTILUS

[Daniel Drake]

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Hi,

As reported here:
http://bugs.gentoo.org/show_bug.cgi?id=254150

.config here:
http://bugs.gentoo.org/attachment.cgi?id=177958&action=view

Compile fails for the CONFIG_ALPHA_NAUTILUS systype on gcc 4.3, due to
gcc's new array bounds checking:
   CC      arch/alpha/kernel/irq_srm.o
cc1: warnings being treated as errors
arch/alpha/kernel/irq_srm.c: In function 'init_srm_irqs':
arch/alpha/kernel/irq_srm.c:69: error: array subscript is above array
bounds
arch/alpha/kernel/irq_srm.c:70: error: array subscript is above array
bounds
make[1]: *** [arch/alpha/kernel/irq_srm.o] Error 1

I was surprised to see that alpha has -Werror set, but I see that is
also true of some other architectures. Ordinarily, bounds checking is
only a warning.

gcc is both right and wrong with this warning. It is right, because
nautilus hits this in arch/alpha/include/asm/irq.h:
#else /* everyone else */
# define NR_IRQS	16
#endif

And init_srm_irqs() would clearly go above the size of the array:
	for (i = 16; i < max; ++i)

But gcc is also wrong, in that it is assuming that init_srm_irqs() would
be called with max > 16. In fact, in this configuration, init_srm_irqs()
is never called at all (but I am not sure how we could expect gcc to
know this, given that object files are compiled individually). It is
only called on two of the many alpha systypes, as far as I can see.

To fix this, we could remove -Werror or we could restructure the irq_srm
code so that it is only compiled on systems that use it. One small
function (srm_device_interrupt) is used all over the place so would have
to be separated. Patch attached, which has been compile-tested on 
nautilus. The disadvantage is that srm_device_interrupt() is now built 
on all alpha sys types, but it is so small that it doesn't seem worth 
creating its own file or creating ifdef spaghetti.

Thoughts?

Daniel


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From: Daniel Drake <dsd@gentoo.org>
https://bugs.gentoo.org/show_bug.cgi?id=254150
Disclaimer: I know nothing about alpha!

Index: linux-2.6.28-gentoo/arch/alpha/kernel/Makefile
===================================================================
--- linux-2.6.28-gentoo.orig/arch/alpha/kernel/Makefile
+++ linux-2.6.28-gentoo/arch/alpha/kernel/Makefile
@@ -57,7 +57,7 @@ obj-$(CONFIG_ALPHA_TITAN)	+= core_titan.
 obj-$(CONFIG_ALPHA_WILDFIRE)	+= core_wildfire.o
 
 # Board support
-obj-$(CONFIG_ALPHA_ALCOR)	+= sys_alcor.o irq_i8259.o irq_srm.o
+obj-$(CONFIG_ALPHA_ALCOR)	+= sys_alcor.o irq_i8259.o
 obj-$(CONFIG_ALPHA_CABRIOLET)	+= sys_cabriolet.o irq_i8259.o irq_srm.o \
 				   ns87312.o
 obj-$(CONFIG_ALPHA_EB164)	+= sys_cabriolet.o irq_i8259.o irq_srm.o \
@@ -78,19 +78,19 @@ obj-$(CONFIG_ALPHA_JENSEN)	+= sys_jensen
 obj-$(CONFIG_ALPHA_MARVEL)	+= sys_marvel.o 
 obj-$(CONFIG_ALPHA_MIATA)	+= sys_miata.o irq_pyxis.o irq_i8259.o \
 				   es1888.o smc37c669.o
-obj-$(CONFIG_ALPHA_MIKASA)	+= sys_mikasa.o irq_i8259.o irq_srm.o
-obj-$(CONFIG_ALPHA_NAUTILUS)	+= sys_nautilus.o irq_i8259.o irq_srm.o
+obj-$(CONFIG_ALPHA_MIKASA)	+= sys_mikasa.o irq_i8259.o
+obj-$(CONFIG_ALPHA_NAUTILUS)	+= sys_nautilus.o irq_i8259.o
 obj-$(CONFIG_ALPHA_NORITAKE)	+= sys_noritake.o irq_i8259.o
 obj-$(CONFIG_ALPHA_RAWHIDE)	+= sys_rawhide.o irq_i8259.o
 obj-$(CONFIG_ALPHA_RUFFIAN)	+= sys_ruffian.o irq_pyxis.o irq_i8259.o
 obj-$(CONFIG_ALPHA_RX164)	+= sys_rx164.o irq_i8259.o
 obj-$(CONFIG_ALPHA_SABLE)	+= sys_sable.o
 obj-$(CONFIG_ALPHA_LYNX)	+= sys_sable.o
-obj-$(CONFIG_ALPHA_BOOK1)	+= sys_sio.o irq_i8259.o irq_srm.o ns87312.o
-obj-$(CONFIG_ALPHA_AVANTI)	+= sys_sio.o irq_i8259.o irq_srm.o ns87312.o
-obj-$(CONFIG_ALPHA_NONAME)	+= sys_sio.o irq_i8259.o irq_srm.o ns87312.o
-obj-$(CONFIG_ALPHA_P2K)		+= sys_sio.o irq_i8259.o irq_srm.o ns87312.o
-obj-$(CONFIG_ALPHA_XL)		+= sys_sio.o irq_i8259.o irq_srm.o ns87312.o
+obj-$(CONFIG_ALPHA_BOOK1)	+= sys_sio.o irq_i8259.o ns87312.o
+obj-$(CONFIG_ALPHA_AVANTI)	+= sys_sio.o irq_i8259.o ns87312.o
+obj-$(CONFIG_ALPHA_NONAME)	+= sys_sio.o irq_i8259.o ns87312.o
+obj-$(CONFIG_ALPHA_P2K)		+= sys_sio.o irq_i8259.o ns87312.o
+obj-$(CONFIG_ALPHA_XL)		+= sys_sio.o irq_i8259.o ns87312.o
 obj-$(CONFIG_ALPHA_SX164)	+= sys_sx164.o irq_pyxis.o irq_i8259.o \
 				   irq_srm.o smc37c669.o
 obj-$(CONFIG_ALPHA_TAKARA)	+= sys_takara.o irq_i8259.o ns87312.o
Index: linux-2.6.28-gentoo/arch/alpha/kernel/irq.c
===================================================================
--- linux-2.6.28-gentoo.orig/arch/alpha/kernel/irq.c
+++ linux-2.6.28-gentoo/arch/alpha/kernel/irq.c
@@ -159,3 +159,11 @@ handle_irq(int irq)
 	__do_IRQ(irq);
 	irq_exit();
 }
+
+void
+srm_device_interrupt(unsigned long vector)
+{
+	int irq = (vector - 0x800) >> 4;
+	handle_irq(irq);
+}
+
Index: linux-2.6.28-gentoo/arch/alpha/kernel/irq_srm.c
===================================================================
--- linux-2.6.28-gentoo.orig/arch/alpha/kernel/irq_srm.c
+++ linux-2.6.28-gentoo/arch/alpha/kernel/irq_srm.c
@@ -71,9 +71,3 @@ init_srm_irqs(long max, unsigned long ig
 	}
 }
 
-void 
-srm_device_interrupt(unsigned long vector)
-{
-	int irq = (vector - 0x800) >> 4;
-	handle_irq(irq);
-}

Re: cant compile on alpha with gcc-4.3 and CONFIG_ALPHA_NAUTILUS

[Ivan Kokshaysky]

On Sat, Jan 10, 2009 at 11:54:15AM +0000, Daniel Drake wrote:
> To fix this, we could remove -Werror or we could restructure the irq_srm
> code so that it is only compiled on systems that use it. One small
> function (srm_device_interrupt) is used all over the place so would have
> to be separated. Patch attached, which has been compile-tested on nautilus. 
> The disadvantage is that srm_device_interrupt() is now built on all alpha 
> sys types, but it is so small that it doesn't seem worth creating its own 
> file or creating ifdef spaghetti.
>
> Thoughts?

Your patch looks fine, but there is simpler fix which makes the compiler
to optimize problematic code away on systems with NR_IRQS <= 16.

Ivan.

diff --git a/arch/alpha/kernel/irq_srm.c b/arch/alpha/kernel/irq_srm.c
index 3221201..a03fbca 100644
--- a/arch/alpha/kernel/irq_srm.c
+++ b/arch/alpha/kernel/irq_srm.c
@@ -63,6 +63,8 @@ init_srm_irqs(long max, unsigned long ignore_mask)
 {
 	long i;
 
+	if (NR_IRQS <= 16)
+		return;
 	for (i = 16; i < max; ++i) {
 		if (i < 64 && ((ignore_mask >> i) & 1))
 			continue;

Re: cant compile on alpha with gcc-4.3 and CONFIG_ALPHA_NAUTILUS

[Daniel Drake]

Ivan Kokshaysky wrote:
> Your patch looks fine, but there is simpler fix which makes the compiler
> to optimize problematic code away on systems with NR_IRQS <= 16.

Yes, I guess that works too. Would you like me to submit that to Andrew 
or are you going to take care of it?

cheers
Daniel