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Date: Thu, 12 Feb 2015 18:07:19 +0100
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai] Mayday mechanism broken on x86-64 - simpler approach
 feasible?
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To: Jan Kiszka <jan.kiszka@siemens.com>, Xenomai <xenomai@xenomai.org>

On 02/12/2015 06:02 PM, Jan Kiszka wrote:
> On 2015-02-12 17:36, Jan Kiszka wrote:
>>> As I mentioned earlier, I'd rather fix the MAYDAY implementation for
>>> x86_64 instead of forking the implementation between MMU-enabled and
>>> MMU-less architectures, also affecting powerpc, arm and x86_32 in the
>>> same move. Fortunately, the current implementation allows very specific
>>> tweaks to be applied on a per-architecture basis. This one fixes the
>>> issue for Cobalt on x86_64, and could be easily backported to 2.6.x:
>>>
>>> http://git.xenomai.org/xenomai-3.git/commit/?h=next&id=6db20901963d634b9786467c711c2ba526db48a2
>>
>> Looks almost good - except for the detail that some bits of the
>> instruction pointer are lost on return from the syscall (int vs. long
>> return type). Patches in the making.
> 
> Will take longer - I need to convert all cobalt syscalls.
> 
> We have a sleeping bug there, though likely not seen in practice, with
> syscalls returning values > INT_MAX (size_t...). The problem is that
> handle_head/root_syscall only forwarded 32-bits so far.
> 

You mean this, and all the implications of it?

diff --git a/kernel/cobalt/posix/syscall.c b/kernel/cobalt/posix/syscall.c
index 6a9a02c..99b86a4 100644
--- a/kernel/cobalt/posix/syscall.c
+++ b/kernel/cobalt/posix/syscall.c
@@ -73,9 +73,9 @@
 /* Shorthand for oneway trap - does not return to call site. */
 #define __xn_exec_oneway    __xn_exec_norestart

-typedef int (*cobalt_syshand)(unsigned long arg1, unsigned long arg2,
-			      unsigned long arg3, unsigned long arg4,
-			      unsigned long arg5);
+typedef long (*cobalt_syshand)(unsigned long arg1, unsigned long arg2,
+			       unsigned long arg3, unsigned long arg4,
+			       unsigned long arg5);

 static void prepare_for_signal(struct task_struct *p,
 			       struct xnthread *thread,

-- 
Philippe.