Question about memmove implemented for uClibc arm

[Khem Raj]

On Thu, 2008-05-22 at 06:34 +0100, 夏Timothy wrote:

> And then, I dig into the telnetd.c for both busybox 1.7.2 and 1.10.2,
> hoping to find out why busybox 1.7.2
> could not work with arm uClibc toolchain. The followings are my
> findings.
>  
> when busybox telnetd receives character from socketd, it would send
> the character to pty. Before sending the 
> character, here are some statements in telnetd.c:
>     char *ptr;
>     /* Write to pty from buffer 1. */
>     ptr = remove_iacs(ts, &num_totty);
>     w = safe_write(ts->ptyfd, ptr, num_totty);
> 
> Here is the statement used to return from remove_iacs in busybox 1.72.
>     return memmove(ptr - num_totty, ptr0, num_totty); 
> While the code used to return from remove_iacs in busybox 1.10.2 turns
> out to be:
>     if ((ptr - totty) == 0) /* 99.999% of cases */
>         return ptr0;
>     return memmove(ptr - num_totty, ptr0, num_totty);
>  
> It seems memmove returns value 0 so that when the following code
> attempts to access *0, error occurs. Thus, it 
> could explain why busybox 1.7.2 fails but busybox 1.10.2 works since
> it returns ptr0 which is safe.
>  
> However, according to GNU Libc definition, the prototype of memmove
> is:
>    void * memmove (void *to, const void *from, size_t size) 
> And the value returned by memmove should be the value of to.
>  
> Hence, I dig into the code of uClibc that implements memmove. And I
> found that for the code of uClibc i386, memmove 
> does return the value of to. But for uClibc arm, memmove just simply
> jumps to a function _memcpy which is implemented 
> by a bunch of assembly code. I suspected that uClibc arm code does not
> implement memmove according to the GNU libc 
> definition and memmove does not return a value of to, instead, it
> returns 0 directly. 
>  
> If so, busybox 1.10.2 might also be not totally safe. There still
> exists possibility that remove_iacs uses memmove to 
> return. 
>  
> Could anybody help me to provide me with some comments on my
> suspicion? Thanks a lot.
>  
> With Regards,
> Timothy
>  
>  

In general many uclibc functions differ from glibc equivalents in
behaviour so do not use the glibc behavior as reference instead look up
SUSV3 for reference. 


However I see that when destination == source than _memcpy returns 0 

ISO  for memmove and memcpy says that functions should return src always

So it seems a bug in arm uclibc to me.

Thanks

-Khem

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