<div>The easiest would be to explicitly serialise the bytes. For instance: <br></div><div>For writing: </div><div>uint32_t t = value;</div><div>buffer[0] = (unsigned char)t; t = t >> 8;</div><div>buffer[1] = (unsigned char)t; t = t >> 8;<br>
</div><div>buffer[2] = (unsigned char)t; t = t >> 8;<br></div><div>buffer[3] = (unsigned char)t;<br></div><div><br></div><div>For reading:</div><div>uint32_t t = buffer[3]; t = t << 8;</div><div>t = t | buffer[2]; t = t << 8;</div>
<div>t = t | buffer[1]; t = t << 8;<br></div><div>t = t | buffer[0]; <br></div><div>value = t;</div><div><br></div><div>This would be the C way, but boost probably already provide endianness-safe serialization.</div>
<div><br></div><div>Before changing the code, just put some cout/printf after the length decoding and check if the length makes sense. And remember that this is just my intuition of where the error could come from because there is definitely a bug there. It might be completely unrelated to your problem, but the symptoms would fit...</div>
<div><br></div><div>Regards</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Nov 28, 2012 at 6:22 PM, Claudio Carbone <span dir="ltr"><<a href="mailto:cla_carbone@tiscali.it" target="_blank">cla_carbone@tiscali.it</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>Thanks for the hint Cedric.<br>
<br>
It's the first time I encounter an endianness problem.<br>
At this point we are not even sure this is an endianness problem.<br>
<br>
I filed a ticket to propose a more descriptive error message in
case of buffer overrun, as the way it is now it's really useless
(just buffer overrun, but no indication of which buffer, what was
the dimension, what was the overrun and how was the dimension
specified).<br>
<br>
By the way: how should I modify the snippet you posted to avoid
endianness problems?<br>
Wouldn't compiling with -mlittle-endian solve such problems?
(trying now, but it will take about 8hrs to compile)<span class="HOEnZb"><font color="#888888"><br>
<br>
Claudio</font></span><div><div class="h5"><br>
<br>
<br>
On 28/11/12 17:46, Cedric Pradalier wrote:<br>
</div></div></div><div><div class="h5">
<blockquote type="cite">Here it is, in roscpp/src/libros, writeHeader
<div> uint32_t msg_len = len + 4;<br>
</div>
<div>
<div> boost::shared_array<uint8_t> full_msg(new
uint8_t[msg_len]);</div>
<div> memcpy(full_msg.get() + 4, buffer.get(), len);</div>
<div> *((uint32_t*)full_msg.get()) = len;</div>
<div><br>
</div>
</div>
<div>and onHeaderLengthRead:</div>
<div>
<div> uint32_t len = *((uint32_t*)buffer.get());</div>
<div><br>
</div>
</div>
<div>This type of code might create some trouble when run between
x86 and arm cpu. However, I could only track this bit of code in
the UDP and service loop, and I only checked that this code was
there up to fuerte.</div>
<div><br>
</div>
<div>In my experience some time ago, I could listen to packet from
a gumstix (cturtle, compressed or raw video) from a x86 laptop
(diamondback I think). So this might actually be two different
bugs...</div>
<div><br>
</div>
<div>Now, for people who wonder why I did not report this earlier:
contributing to ros_comm has not been very successful so far on
my side, so I just keep track of my patches until someone really
needs them... (shared memory and compressed transports
out-of-the-box for all topics?)</div>
<div><br>
</div>
<div>Regards</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Wed, Nov 28, 2012 at 5:14 PM,
Claudio Carbone <span dir="ltr"><<a href="mailto:cla_carbone@tiscali.it" target="_blank">cla_carbone@tiscali.it</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>Thank you Cedric,<br>
<br>
I'll wait for your info.<br>
<br>
Regards<span><font color="#888888"><br>
-- <br>
</font></span>
<div>
<div>
<p><b><span style="color:#262626">Eng. Claudio
Carbone<br>
Embedded Systems Design</span></b><span style="color:#7f7f7f"> <br>
</span></p>
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</p>
</div>
<div>
<p class="MsoNormal"><br>
On 28/11/12 17:09, Cedric Pradalier wrote:<br>
</p>
<blockquote type="cite">Hi,
<div><br>
</div>
<div>last time I checked, some of the
deserialization code was actually endianness
specific (if I'm not mistaken), in particular
the length of the message... This could lead
easily to a buffer overrun.</div>
<div><br>
</div>
<div>I'll try to point out the little bit of code
later today.</div>
<div><br>
</div>
<div>Regards<br>
</div>
</blockquote>
<br>
</div>
</div>
</div>
</div>
<br>
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</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
Cedric Pradalier<br>
</div>
<br>
<fieldset></fieldset>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br>Cedric Pradalier<br>
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