[Valgrind-users] baffled by vg output

[Tristan V. B. <va...@to...>]

Hi all,
    I've been fooling around with valgrind (very impressed btw) and I'm not
100% clear on all the program output.

firstly, maybe there is an available FAQ for understanding vg output ?
I checked the usual culprits i.e. vg.sf.net && sf.net/projects/vg and 
couldn't
find such a beast.

secondly, if anyone understands this better that I do that would be 
great ;-)
this is what is presently baffeling me:

==1854== Syscall param socketcall.sendto(msg) contains uninitialised or 
unaddressable byte(s)
==1854==    at 0x408E2D92: __libc_sendto (in /lib/libc-2.1.3.so)
==1854==    by 0x40815AA6: trans_send (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)
==1854==    by 0x40813D63: evts_send (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)
==1854==    by 0x40814A0F: sync_call (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)

the "msg" param in my case is definitly initialized (even added memset 
to be sure).
now what could be meant by "unaddressable bytes" ? could this be a 
result of sending
a message of 63 bytes instead of 64 (meaning only one of every 4 bytes 
is "truely addressable") ?
I'm not feeding `sendto' any register variables if thats what it is 
supposed to mean.

==1854==    Address 0x42193CB0 is 60 bytes inside a block of size 63 alloc'd
==1854==    at 0x40166498: malloc (in /usr/lib/valgrind/valgrind.so)
==1854==    by 0x40815A2E: trans_send (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)
==1854==    by 0x40813D63: evts_send (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)
==1854==    by 0x40814A0F: sync_call (in 
/usr/local/touchtunes/lib/libttipc.so.0.0.0)

and this is what follows directly after the previous message.
funny, ("0x42193CB0" - ( decimal 60 )) == "0x42193C74"
which happens to be the pointer to my 63 byte long message.
Is there something wrong with address 0x42193CB0 ? why are my trailing
3 bytes no good or "nonaddressable" ?

might as well have said that:
     "Address 0x42193CB1 is 61 bytes inside a block of size 63 alloc'd"

but how does that help me ?


Cheers all; any help is appriciated ;-)
                            -Tristan


PS:
    valgrind-1.9.6
    glibc-2.2
    linux-2.4.16