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SubjectRe: Linux 2.6.24-rc7 Build-Failure at __you_cannot_kmalloc_that_much
Hi Andrew, hi Chritoph,

On Mon, 7 Jan 2008 11:38:31 -0800, Andrew Morton wrote:
> On Mon, 7 Jan 2008 10:31:53 -0800 (PST)
> Christoph Lameter <clameter@sgi.com> wrote:
>
> > On Mon, 7 Jan 2008, Andrew Morton wrote:
> >
> > > > : undefined reference to `__you_cannot_kmalloc_that_much'
> >
> > There is also a kernel.org bugzilla for this at
> >
> > http://bugzilla.kernel.org/show_bug.cgi?id=9669
> > For some reason my adds to this do not show up.
> >
> > In both cases we have a
> >
> > k(z/m)alloc(sizeof(*pointer), ...)
> >
> > that is for some reason failing. I guess what happens is that the function
> > in which this occurs is too complex for gcc 3.2. Thus it stops constant
> > folding the sizeof(*pointer) in the complex inline-if-cascade that SLAB
> > needs to determine the cache and does not eliminate the
> > __you_cannot_kmalloc_that_much branch().

Interesting theory... So I tried to split half of the code of
dmi_id_init() to a subfunction and bingo! gcc 3.2.3 is now able to
build it properly. Thanks for the hint!

> > SLUB in that case just puts a series of if comparisions in the code. This
> > means compilation does not fail but a large amount of code is generated.
>
> ug. Silent and nasty.
>
> > We could replace the __you_cannot_kmalloc_that_much() with a BUG()
> > statement so we have the same effect in SLAB?
>
> I think it'd be better to just put suitable workarounds at the offending
> callsites. We've only seen three or four of them in several months.

Here's a workaround for dmi-id.

Subject: Fix for __you_cannot_kmalloc_that_much failure in dmi-id

gcc 3.2 has a hard time coping with the code in dmi_id_init():

drivers/built-in.o(.init.text+0x789e): In function `dmi_id_init':
: undefined reference to `__you_cannot_kmalloc_that_much'
make: *** [.tmp_vmlinux1] Error 1

Moving half of the code to a separate function seems to help. This is
a no-op for gcc 4.1 which will successfully inline the code anyway.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
---
drivers/firmware/dmi-id.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

--- linux-2.6.24-rc7.orig/drivers/firmware/dmi-id.c 2007-10-24 09:59:28.000000000 +0200
+++ linux-2.6.24-rc7/drivers/firmware/dmi-id.c 2008-01-08 10:32:00.000000000 +0100
@@ -175,12 +175,11 @@ static struct device *dmi_dev;

extern int dmi_available;

-static int __init dmi_id_init(void)
+/* In a separate function to keep gcc 3.2 happy - do NOT merge this in
+ dmi_id_init! */
+static void __init dmi_id_init_attr_table(void)
{
- int ret, i;
-
- if (!dmi_available)
- return -ENODEV;
+ int i;

/* Not necessarily all DMI fields are available on all
* systems, hence let's built an attribute table of just
@@ -205,6 +204,16 @@ static int __init dmi_id_init(void)
ADD_DMI_ATTR(chassis_serial, DMI_CHASSIS_SERIAL);
ADD_DMI_ATTR(chassis_asset_tag, DMI_CHASSIS_ASSET_TAG);
sys_dmi_attributes[i++] = &sys_dmi_modalias_attr.attr;
+}
+
+static int __init dmi_id_init(void)
+{
+ int ret;
+
+ if (!dmi_available)
+ return -ENODEV;
+
+ dmi_id_init_attr_table();

ret = class_register(&dmi_class);
if (ret)
I'll now check if I can do something similar for snd-mixer-oss.

--
Jean Delvare


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