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Re: [Qemu-devel] qemu-ppc can't run static uClibc binaries.

From: Alexander Graf
Subject: Re: [Qemu-devel] qemu-ppc can't run static uClibc binaries.
Date: Tue, 16 Feb 2010 19:36:15 +0100

On 16.02.2010, at 19:31, Rob Landley wrote:

> On Monday 15 February 2010 07:01:02 Alexander Graf wrote:
>> On 15.02.2010, at 13:58, Rob Landley wrote:
>>> On Monday 15 February 2010 05:19:24 Alexander Graf wrote:
>>>> On 15.02.2010, at 12:10, Rob Landley wrote:
>>>>> On Sunday 14 February 2010 08:41:00 Alexander Graf wrote:
>>>>>> So the only case I can imagine that this breaks anything is that
>>>>>> uClibc requires register state to be 0.
>>>>> Yes, r3 (which is the exit code from the "exec" syscall, and thus 0 if
>>>>> it worked).  In the BSD layout, it's argc (which can never be 0).
>>>>> http://lists.gnu.org/archive/html/qemu-devel/2007-03/msg00720.html
>>>> So what you really want is something like
>>>> /* exec return value is always 0 */
>>>> env->gpr[3] = 0;
>>>> #endif
>>>> just after the #endif in your patch. If you had inlined your patch I
>>>> could've commented it there.
>>> Unfortunately kmail plays fast and loose with whitespace when I inline
>>> stuff. (Not always, but I can't tell by inspection when it's decided it
>>> was hungry for tabs or wanted to throw in that horrible UTF8 escaped
>>> whitespace.)
>> git-send-mail is your friend :-).
> No git command is my friend.  The user interface of that monstrosity should 
> be 
> <strike>condemned</strike> banished with full bell book and dribbly candles.
> And I dunno how it would interface with kmail.  (No other program on my 
> laptop 
> has the ssh tunnel to my mail server set up so it can send anything.)  But 
> out 
> of curiosity...
>  address@hidden:~$ git send-mail
>  git: 'send-mail' is not a git-command. See 'git --help'.
>  address@hidden:~$ git-send-mail
>  bash: git-send-mail: command not found
>  address@hidden:~$ git send mail
>  git: 'send' is not a git-command. See 'git --help'.
> Since it's unlikely that this could send a patch I haven't checked into git 
> (and I generally treat git as a read-only resource), learning more about it 
> goes on the todo list I expect.
>>> I didn't explicitly set it because they're initialized to zero in
>>> function main() on line 2654 of linux-user/main.c.  (Any regs we don't
>>> explicitly set to some other value start out zeroed in qemu.)
>> So it should work already?
> *shrug*  It doesn't.
> Let's see, one of the lines I #ifdefed out (line 535-ish of linux-
> user/elfload.c) is:
>    get_user_ual(_regs->gpr[3], pos);
> Rummage, rummage... get_user_ual() is a wrapper for get_user() which is a 
> wrapper for __get_user() which assigns to its first argument.  So yeah, 
> that's 
> setting _regs->gpr[3] to a nonzero value.

Well I was wondering on the order of execution. If main() already sets the GPRs 
to 0 it should be 0. I assume the elf reading code comes after that? If so, 
your patch looks correct.


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