[vbox-dev] "An invalid or unaligned stack was encountered during an unwind operation" in VBoxREM.dll

Rūdolfs Bundulis rudolfs.bundulis at gmail.com
Tue Oct 28 13:38:37 UTC 2014


one more thing that I could find out in the sources but at this point if
someone knows it would save time - are there any alignment constraints on
the VRAM memory that is passed to the IFramebuffer object via the in
octetPtr VRAM parameter? I would eventually need this memory to be 16-byte
aligned but I already planned that I will have to do something about this,
however if VirtualBox already gives some alignment guarantees it would be
nice to know that I don't have to think about this.

2014-10-28 13:30 GMT+02:00 Rūdolfs Bundulis <rudolfs.bundulis at gmail.com>:

> Hi Klaus,
> thanks for the explanations, I'll try running the software under gdb to
> get more info - most likely it is my fault, simply with the current
> information from Visual Studio I've got zero hints. Thanks.
> 2014-10-28 12:39 GMT+02:00 Klaus Espenlaub <klaus.espenlaub at oracle.com>:
>> Rūdolfs,
>> On 27.10.2014 22:39, Rūdolfs Bundulis wrote:
>> > Hi,
>> >
>> > my custom frontend for VirtualBox seemed to work fine and stable but
>> > then I started to play around with number of CPU's and memory and I
>> > started getting "An invalid or unaligned stack was encountered during an
>> > unwind operation" from VBoxREM.dll. I downloaded the sources for
>> > VirtualBox 4.3.18, built it for x64 debug and started debugging.
>> >
>> > * The first weird thing was that I could not find a .pdb file for
>> > VBoxREM.dll, is that some kind of special .dll? I have pdb files for
>> > VBoxC.dll and friends under "out\win.amd64\debug\stage\debug\bin" but I
>> > can't find one for VBoxREM.dll.
>> That's expected... VBoxREM.dll is very special, it contains the (qemu)
>> recompiler, which must be built using gcc, and that's the reason why
>> there are no pdb files for it. It should contain dwarf debug info
>> straight in the dll, which gdb understands. Yes, it's annoying because
>> one has to pick the right debugger straight from the beginning.
>> > * The stack trace is (I know it won't give much help):
>> >
>> > ntdll.dll!00007ffe679ac0b4()Unknown
>> > ntdll.dll!00007ffe67913356()Unknown
>> > msvcrt.dll!__longjmp_internal ()Unknown
>> >  >VBoxREM.dll!000000006fb0f3c4()Unknown
>> >
>> > The frontend does not have any output from VirtualBox on stdout or
>> > stderr and the logfile also does not show any errors.
>> >
>> > Could anyone provide any pointers how should I approach debugging this?
>> Hope gdb is helpful.
>> On modern hardware which supports VT-x/AMD-V it's somewhat unexpected
>> that you end up in the recompiler, but there are some corner cases which
>> it is still used for.
>> Klaus
>> >
>> > Best Regards,
>> > Rudolfs Bundulis
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