Re: [PATCH] compat_audit: allow it to work without asm/unistd32.h

From: AKASHI Takahiro
Date: Mon Mar 24 2014 - 22:16:55 EST


On 03/25/2014 01:39 AM, Chris Metcalf wrote:
The problem is that audit_is_compat() is a dynamic test that the compiler
can't optimize away, so you end with an undefined reference to
audit_classify_compat_syscall().

For some reason audit_classify_compat_syscall() is declared as __weak
in <linux/audit.h>; usually the __weak tag is only provided on the definition.
But I suppose you could imagine providing a weak definition in lib/audit.c
itself.

I still believe that a function can be declared with __weak and replaced
by a strong definition later on (at link time).
But this is not the case anyway.

Or there could be a CONFIG_AUDIT_COMPAT symbol that architectures need to
set if they want to have audit_is_compat() return anything other than "false",
and then just use that symbol in the #ifdef in <uapi/linux/audit.h>. In that
case the compiler would optimize away the call to audit_classify_compat_syscall().

My guess is that the second option is probably cleanest.

Yep, but I don't want to add new CONFIG_AUDIT_COMPAT symbol just for
audit_is_compat() because it is only used in lib/audit.c(AUDIT_GENERIC).
Instead, I prefer
#ifdef CONFIG_AUDIT_COMPAT_GENERIC
#define audit_is_compat(arch) (...)
#else
#define audit_is_compat(arch) false
#endif

Thanks,
-Takahiro AKASHI

On 3/24/2014 12:21 PM, Eric Paris wrote:
I don't know tilegx, but I have replaced 223b24d807610 with
4b58841149dcaa5. I believe adding AUDIT_ARCH_COMPAT_GENERIC was
akashi-san's fix for this problem on mips. Is this a better fix?

Thanks
-Eric

On Thu, 2014-03-20 at 11:31 -0400, Chris Metcalf wrote:
For architectures that use the asm-generic syscall table for both
32- and 64-bit, there should be no need to provide a separate
<asm/unistd32.h>; just using <linux/unistd.h> is sufficient.
Conditionalize use of <asm/unistd32.h> on the one platform that
currently requires it (arm64). If another platform ends up needing
it we can create a suitable config flag at that point.

This change fixes the tilegx build failure seen in linux-next.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
By the way - I also note that commit 223b24d807610 that introduced
this also put an "#ifdef COMPAT_xxx" in a UAPI header. This seems
like a pretty clear signal that the added code should be in
linux/include/audit.h, not linux/uapi/include/audit.h. But here
I'm just focussing on getting tilegx to continue to build...

lib/compat_audit.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/compat_audit.c b/lib/compat_audit.c
index 873f75b640ab..e89a84b3fbe8 100644
--- a/lib/compat_audit.c
+++ b/lib/compat_audit.c
@@ -1,6 +1,11 @@
#include <linux/init.h>
#include <linux/types.h>
-#include <asm/unistd32.h>
+#ifdef COMPAT_ARM64
+/* 64-bit syscalls are generic, but 32-bit are not. */
+# include <asm/unistd32.h>
+#else
+# include <linux/unistd.h>
+#endif

unsigned compat_dir_class[] = {
#include <asm-generic/audit_dir_write.h>


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