Hi,
Thanks for the help. I have disassembled the code. However.if I post them here,
the mail would be very very long.
Actually, I think the assembly code for memmove and memcopy could be found in
uClibc/libc/string/arm/memmove.S and uClibc/libc/string/arm/_memcpy.S
respectively.
Would that help? Thanks.
Best Regards,
Timothy
> From: [EMAIL PROTECTED]> To: [email protected]> Subject: Re: Question about
> memmove implemented for uClibc arm> Date: Thu, 22 May 2008 09:23:53 +0200>
> CC: [EMAIL PROTECTED]> > On Thursday 22 May 2008 07:34, 夏Timothy wrote:> >
> Hi, all> > > > I have built a arm uClibc toolchain from buildroot. The gcc
> version is 4.2.3 and uClibc used is snapshot.> > > > Normally, I build
> busybox 1.7.2 with codesourcery toolchain and everything works fine.> > > >
> Then I tried to build buxybox 1.7.2 with arm uClibc toolchain. And it turns
> out the telnetd for busybox 1.7.2 > > does not work functionally. When I
> telnet to the arm developement board, on which linux and busybox 1.7.2 is > >
> running, I got a shell prompt. But no matter which keyboard button I pressed,
> the connect would be closed.> > > > Consequently, I tried to build busybox
> 1.10.2 and it turned out that telnetd for busybox 1.10.2 could work> >
> correctly. > > > > 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.> > Excellent
> analysis.> > Can you disassemble "working" and "broken" memmove (and memcpy)
> code?> > If you build static busybox, dump busybox_unstripped binaries:> >
> <TARGET_PREFIX>-objdump -dr busybox_unstripped> > If you use shared uclibc,
> you need to dump libuClibc-$VERSION.so instead.> > Yon may need to add some
> switches to get arm/thumb disasm sorted out.> > Find memmove and memcpy
> assembly code in the output and post to the list.> --> vda
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