I sent a question yesterday, but I don't see it as having been posted, much 
less 
responded to. My apologies for the redundancy if my original message is in 
some 
queue somewhere.

**********

I'm trying to determine the utility of Valgrind in an app. The app uses 
protocol buffers.

I am seeing a message from Valgrind

Syscall param write(buf) points to uninitialised byte(s)

with the following info

Address 0x11c7fa02 is 2 bytes inside a block of size 8,192 alloc'd

At first, I thought it might be one of the fields in a message declared 
optional, but 
when I filled out the field, I got the same warning. In the process of 
looking into this 
more closely I was able to dump the buffer:

0x00    0x01    0xc1    0x09    0x00    0x00    0x00    0x10 <---- secret, 
pre-header?
0x08    0x00    0x10    0xa5    0xcb    0x96    0xad    0x0a
0x1a    0x06    0x61    0x70    0x61    0x63    0x68    0x65

The latter 16 bytes are the message proper with three fields and I 
understand how 
they are created and interpreted from the Encoding spec (very helpful). It 
is the first 
eight bytes I don't  understand.

These first bytes are almost like a secret pre-header. It looks to me as if 
the last four 
bytes are a 32-bit length field. The number matches in this case and in the 
other case in 
which the optional field was left unset. I can't figure what the first four 
bytes indicate. In
particular, the bytes 0xc1 and 0x09, which would start the area of the 
supposedly 
uninitialized bytes.

Is there somewhere in the code I can look to see how this pre-header is 
created. Or I 
would be happy to research this myself if some documentation exists, but I 
don't know
where to start looking.

Thanks for any help,
jdm

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