linux-kernel - Re: [LKP] [PATCH] drm/radeon: Try to init amdkfd only if 64 bit kernel

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Date:	Wed, 24 Dec 2014 09:31:13 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Oded Gabbay <oded.gabbay@....com>, Andi Kleen <ak@...ux.intel.com>,
	Alex Deucher <alexdeucher@...il.com>
Cc:	Dana Elifaz <Dana.Elifaz@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>,
	Alexander Deucher <Alexander.Deucher@....com>,
	LKP ML <lkp@...org>
Subject: Re: [LKP] [PATCH] drm/radeon: Try to init amdkfd only if 64 bit kernel

Oded Gabbay <oded.gabbay@....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.
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