Re: [PATCH mm] kfence: fix printk format for ptrdiff_t

From: Christophe Leroy
Date: Wed Mar 17 2021 - 13:37:21 EST

Le 17/03/2021 à 13:51, David Laight a écrit :
From: Christophe Leroy
Sent: 16 March 2021 15:41
include/linux/types.h:typedef __kernel_ptrdiff_t ptrdiff_t;

And get:

CC mm/kfence/report.o
In file included from ./include/linux/printk.h:7,
from ./include/linux/kernel.h:16,
from mm/kfence/report.c:10:
mm/kfence/report.c: In function 'kfence_report_error':
./include/linux/kern_levels.h:5:18: warning: format '%td' expects argument
of type 'ptrdiff_t', but argument 6 has type 'long int' [-Wformat=]

This is declared as
const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
so maybe something with that goes wrong? What happens if you delete the
(useless) "const" here?

The obvious thing to try is changing it to 'int'.
That will break 64bit builds, but if it fixes the 32bit one
it will tell you what type gcc is expecting.

Yes, if defining 'object_index' as int, gcc is happy.
If removing the powerpc re-definition of ptrdiff_t typedef in , it works great as well.

So seems like gcc doesn't take into account the typedef behind ptrdiff_t, it just expects it to be int on 32 bits ?