cap_disas_plugin leaks memory

[Robert Henry]

Looking at origin/master head, the function cap_disas_plugin leaks memory.

per capstone's examples using their ABI, cs_free(insn, count); needs to called just before cs_close.

I discovered this running qemu under valgrind.

[Alex Bennée (ajbennee)]

It looks like this will fail on all the other capstone cases as well. Is this an API change across versions?

[Robert Henry (mhodog)]

I run git blame in the capstone repository, and cs_free has been around for at least 4 years in the capstone ABI. I can not tell if the need to call cs_free is a (new) requirement. Documentation capstone is a little informal...

[Alex Bennée (ajbennee)]

What command line where you using? I've been unable to replicate the valgrind warning with a riscv64-linux-user run of hello with the libhowvec.so plugin. Valgrind does complain about a bunch of other stuff though.

[Alex Bennée (ajbennee)]

Looking at the way disas is structured it seems cap_insn is allocated once (per thread) and re-used for each disassembly so we shouldn't be free'ing it after each usage. In fact the comments to cap_disas_start imply we want to do better than re-initialising the library for every set of instructions we disassemble.

It is true that we don't clean-up any of the disassembly machinery on exit but the same can be said for a lot of QEMU's static state. So currently I don't see a leak rather than a one-time allocation. Unless I can reproduce the leak I'm going to mark this as incomplete for now.

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]