Re: [PATCH] x86_32: Fix module version table mismatch.

From: James Hogan
Date: Wed Apr 24 2013 - 06:14:08 EST

On 24/04/13 02:00, H. Peter Anvin wrote:
> On 04/23/2013 05:52 PM, H. Peter Anvin wrote:
>> On 04/23/2013 05:40 AM, Tetsuo Handa wrote:
>>> Commit a4b6a77b "module: fix symbol versioning with symbol prefixes" broke
>>> loading of net/ipv6/ipv6.ko built with CONFIG_MODVERSIONS=y for x86_32.
>> This really does seem to be the offending commit, although I'm still
>> confused how the heck that is possible.
> OK, now I grok.
> The bug is the use of VMLINUX_SYMBOL_STR(%s) which expands at the time
> the output of modpost is compiled. However, VMLINUX_SYMBOL_STR() unlike
> __VMLINUX_SYMBOL_STR() does macro expansion on its argument, which is
> actively wrong here.

Yes, nasty bug there (sorry!)

> I think the choice is either to change this to __VMLINUX_SYMBOL_STR() or
> re-introduce CONFIG_SYMBOL_PREFIX (or its equivalent) so that modprobe
> can emit it at compile time

Using __VMLINUX_SYMBOL_STR looks like the correct solution to me.

> (assuming there even should *be* a prefix on
> the symbol here, i.e. that the compiler won't add it.)

[__]VMLINUX_SYMBOL_STR expands to a string (e.g. "_" "memcmp" or just
"memcmp") so the compiler won't touch it.

> Either way -- James, Rusty, this is in your court.

How does the patch below look? I presume this is preferred over
making VMLINUX_SYMBOL_STR non-argument-expanding?


Subject: [PATCH 1/1] modpost: fix unwanted VMLINUX_SYMBOL_STR expansion

Commit a4b6a77b77ba4f526392612c2365797fab956014 ("module: fix symbol
versioning with symbol prefixes") broke the MODVERSIONS loading of any
module using memcmp (e.g. ipv6) on x86_32, as it's defined to
__builtin_memcmp which is expanded by VMLINUX_SYMBOL_STR. Use
__VMLINUX_SYMBOL_STR instead which doesn't expand the argument.

Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
scripts/mod/modpost.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 1f90961..a4be8e1 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1957,7 +1957,7 @@ static int add_versions(struct buffer *b, struct module *mod)
s->name, mod->name);
- buf_printf(b, "\t{ %#8x, VMLINUX_SYMBOL_STR(%s) },\n",
+ buf_printf(b, "\t{ %#8x, __VMLINUX_SYMBOL_STR(%s) },\n",
s->crc, s->name);


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