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From Gregory Shimansky <gshiman...@apache.org>
Subject Re: [M3] NPE is thrown while debugging with M3
Date Fri, 12 Oct 2007 17:24:17 GMT
Tim Ellison wrote:
> Gregory Shimansky wrote:
>> Tim Ellison wrote:
>>> Andrew Zhang wrote:
>>>> On 10/11/07, Tim Ellison <t.p.ellison@gmail.com> wrote:
>>>>> Is that something we need to add to a technical FAQ?
>>>> yeah, I think it would be really helpful!
>>> There is a (short) technical FAQ in this page:
>>>   https://svn.apache.org/repos/asf/harmony/standard/site/xdocs/faq.xml
>>> Perhaps you could add in the symptoms and instructions for disabling the
>>> NX bit?
>> Is this text ok for FAQ?
>> The symptom seems to be unexpected NPEs in the code that doesn't produce
>> any when not debugged. This is a limitation of M3 build. Hopefully it
>> will be fixed in M4.
> Hmm, well if it will be fixed in M4 perhaps it should go into the M3
> release notes as a known issue rather than as a permanent technical FAQ.

In fact I think I've fixed this bug in revision 584204. Andrew, could 
you please try to run this version of DRLVM? I added functions to 
allocate memory with specified permissions and now JVMTI buffer for 
handling breakpoints should have execute permission on it.

>> On Linux ia32 NX bit is usually disabled because enabling it requires
>> CONFIG_X86_PAE that is needed to address over 4Gb of memory, and to turn
>> it on it is necessary to specify "noexec=on" on kernel command line.
>> On Linux x86_64 NX bit is enabled by default, so if one tries to run
>> DRLVM debugger in x86 emulation mode it is better to specify
>> "noexec=off" on kernel command line.
>> On Windows x86 NX bit is controlled with a /noexecute switch to kernel
>> command line in X:\boot.ini (X is boot drive letter) file. Usually it is
>> set as /noexecute=optin that disables execution of kernel but allows
>> execution of user level programs heap. For more details see [1]
>> [1] http://www.microsoft.com/technet/sysinternals/information/bootini.mspx


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