[Valgrind-users] Invalid read/write in memory mapped segments

[Deene D. <Dee...@ma...>]

Hi all,

Recently I've been seeing some Memcheck Invalid read/writes in memory mapped segments, both anonymous and file mapped.
These issues end up being reported in the dlopen code or basic string manipulation code run by the dlopen lib.
e.g.
                IVR or IVW
dl_...
<my application stack...>
Address 0x406005c is in a rw- anonymous segment
OR
Address 0x14758664 is in a r-x mapped file /lib/x86_64-linux-gnu/libz.so.1.2.7 segment

I'm just curious if there is any 'special meaning or actions to take' with these issues being in mapped address space or should I simply treat them as I would any other IVR/IVW (i.e. addr allocated on stack or heap)?

What is an example of an invalid read/write in these cases?

Using a test program I tried writing into an un-mapped addr space and changing the mem protection of an anonymous mapping but in both cases the issue didn't report being in the mapped space; the issues were an IVW with 'not stack'd, malloc'd or (recently) free'd' and a segv (Access not within mapped region at address ...) respectively.

Looking at the test code in the 3.11 source I see some code using VALGRIND_CHECK_MEM_IS_DEFINED and mprotect to generate an issue with an 'rw-anonymous segment' error.

Thanks!