9:16 a.m.
On 12/24/2014 01:01 AM, Rusty Russell wrote:
Oded Gabbay <oded.gabbay(a)amd.com> writes:
> I didn't say it doesn't always work.
> The actual thing that doesn't work is the define symbol_get and only in a
> specific case of 32bit kernel AND CONFIG_MODULES is unset AND
> CONFIG_RANDOMIZE_BASE is set.
> The define in that case is:
> #define symbol_get(x) ({ extern typeof(x) x __attribute__((weak)); &(x); })
>
> Why it doesn't work (doesn't return NULL when symbol doesn't exists) ?
Hmm, I'd guess CONFIG_RANDOMIZE_BASE is relocating NULL symbols...
No, I can't reproduce this. Please send your .config privately.
Here's my test case:
diff --git a/init/main.c b/init/main.c
index 61b993767db5..a3ee1ec97ec3 100644
--- a/init/main.c
+++ b/init/main.c
@@ -683,6 +683,12 @@ asmlinkage __visible void __init start_kernel(void)
ftrace_init();
+ {
+ extern void nonexistent_fn(void);
+ printk("symbol_get(nonexistent_fn) = %p\n",
+ symbol_get(nonexistent_fn));
+ }
+
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}
Thanks,
Rusty.
Hi Rusty,
Attached is the bad config file. (config-bad)
I have narrowed the changes you need to do to the config file in order to
reproduce this bug.
The base assumption is a 32-bit kernel and without modules support. Rest of the
config file is pretty standard, IMO.
Then, its not enough to enable CONFIG_RANDOMIZE_BASE like I wrote in my original
post. You need also to unset CONFIG_HIBERNATION.
If you do only one of the changes above, it isn't sufficient to trigger the problem.
I also attached a config-good file, which is almost the same as config-bad,
except the changes I mentioned above that reproduces the problem.
To quickly reproduce it, I run the following command:
qemu-system-i386 -enable-kvm -kernel arch/x86/boot/bzImage -initrd
~/tmp/test32.cpio.gz
The kernel is 3.19-rc1 from Linus' tree. No additional patches on top of that.
Also attached is the test32.cpio.gz so you could immediately reproduce this.
I appreciate your help.
Oded