[Mono-list] Problem with sgen

[Rodrigo Kumpera]

That's a false positive. sgen conservatively scans the stack and this does
trip valgrind.

On Fri, Nov 21, 2014 at 10:29 AM, terender <terender at hotmail.com> wrote:

> There is a memory problem with mono-sgen on linux. I'm using some pinned
> byte[] buffers in my project, and there's a randomly crash with signal
> SIGSEGV, it could happen anywhere at anytime.
>
> I guess there's some write oprations out of bound in memory, so I use
> valgrind to check the program.
>
> Then I found that a while after the program start within some alloc
> oprations, valgrind report a problem in sgen that is:
>
> ==6504== Thread 1:
> ==6504== Conditional jump or move depends on uninitialised value(s)
> ==6504==    at 0x5C4D46: conservatively_pin_objects_from (sgen-gc.c:1200)
> ==6504==    by 0x5C5322: scan_thread_data (sgen-gc.c:3778)
> ==6504==    by 0x5CA7BA: collect_nursery (sgen-gc.c:2298)
> ==6504==    by 0x5CB877: sgen_perform_collection (sgen-gc.c:3196)
> ==6504==    by 0x5E8CCF: mono_gc_alloc_obj_nolock (sgen-alloc.c:315)
> ==6504==    by 0x5E90E3: mono_gc_alloc_obj (sgen-alloc.c:491)
> ==6504==    by 0x40C09E2: ???
> ==6504==    by 0x4198331: ???
> ==6504==    by 0x40BBF42: ???
> ==6504==    by 0x41DE33: mono_jit_runtime_invoke (mini.c:6738)
> ==6504==    by 0x5A252A: mono_runtime_invoke (object.c:2831)
> ==6504==    by 0x5A5DCF: mono_runtime_exec_main (object.c:4096)
> ==6504==  Uninitialised value was created by a stack allocation
> ==6504==    at 0x57D2E0: start_wrapper (threads.c:701)
>
>
> Any read or write oprations right after that would trigger an Invalid
> write/read error in valgrind and then process got killed.
>
> Is that a bug in sgen collect_nursery with pinned objects in nursery heap?
>
> I have checked on both mono 3.2.3 and 3.10.0,  and I'm using tarball to
> compile them myself.
> The enviroment is CentOS 6.6  Kernal 2.6.32-358.6.2.el6.x86_64, GCC version
> 4.4.7
>
> I could upload the whole log of valgrind for both mono 3.2.3 and 3.10.0 if
> needed.
>
>
> Btw: the problem does not happen if I use boehm
>
>
>
>
> --
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