Re: 2.6.8-rc2-mm1 link errors

[Dave Hansen <haveblue@us.ibm.com>]

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On Wed, 2004-07-28 at 16:49, Andrew Morton wrote:
> Nope.   Could you take a look at the code in the top-level
> Makefile which is doing this, work out why it broke?

It seems to come down to this warning:

arch/i386/kernel/irq.c
{standard input}: Assembler messages:
{standard input}:3565: Warning: setting incorrect section type for
.bss.page_aligned

Which comes from this code in the 4k stacks code:

static char softirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE), __section__(".bss.page_aligned")));
static char hardirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE), __section__(".bss.page_aligned")));

Removing the __section__() fixes it, as does moving to gcc 3.2 or 3.3,
but gcc 2.95 and 3.0 still exhibit the problem.  It seems the 4k stack
developers like newer compilers than I do :) 

The gcc 2.95 section declaration looks like this:
	.section        .bss.page_aligned,"aw",@progbits
while the 3.1 section looks like this:
	.section        .bss.page_aligned,"aw",@nobits

It's definitely a bug that's been fixed:
http://sources.redhat.com/ml/binutils/2002-10/msg00507.html

I've been told that I can fix it with a carefully crafted assembly file
and maybe a change to the linker script, but all that it buys us is a
little space in the uncompressed kernel image.  Plus, the warning will
still be there at compile-time.  

I say, put them back in plain old BSS.  Patch attached.

-- Dave

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diff -rup linux-2.6.8-rc2-mm1/arch/i386/kernel/irq.c linux-2.6.8-rc2-mm1-irqstackbss/arch/i386/kernel/irq.c
--- linux-2.6.8-rc2-mm1/arch/i386/kernel/irq.c	2004-07-28 18:10:40.000000000 -0700
+++ linux-2.6.8-rc2-mm1-irqstackbss/arch/i386/kernel/irq.c	2004-07-28 18:52:41.000000000 -0700
@@ -1118,8 +1118,12 @@ void init_irq_proc (void)
 
 
 #ifdef CONFIG_4KSTACKS
-static char softirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE), __section__(".bss.page_aligned")));
-static char hardirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE), __section__(".bss.page_aligned")));
+/* 
+ * These should really be __section__(".bss.page_aligned") as well, but
+ * gcc's 3.0 and earlier don't handle that correctly.
+ */
+static char softirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE)));
+static char hardirq_stack[NR_CPUS * THREAD_SIZE]  __attribute__((__aligned__(THREAD_SIZE)));
 
 /*
  * allocate per-cpu stacks for hardirq and for softirq processing