When javaFrameAnchor::_last_Java_sp == NULL for a non-first entry frame

[Xiaobin Lu]

I don't think I know why _last_Java_sp is NULL. However, to explain why 
you saw different stack pointer value on different Linux environment, 
take a look at os_linux.cpp, there are about 40 lines of comments 
talking about "thread stack" related things on different Linux 
implementations.

-Xiaobin

On 11/19/09 18:10, Hiroshi Yamauchi wrote:
> Hi,
>
> In AsyncGetCallTrace, I observe
>
>   javaFrameAnchor::_last_Java_sp == NULL
>
> in non-first entry frames on Linux/x86. It is the condition for the
> entry frame to be a first frame. So, I get truncated stack traces
> because stack walk stops at the false first frame.
>
> I thought that the contract was that the _last_Java_sp != NULL for all
> non-first entry frames. Is it correct?
>
> Strangely I see the behavior on one Linux environment (kernel, libc,
> other libraries) but not on another Linux environment (Ubuntu). But
> I'm not sure how the environment could affect the _last_Java_sp field.
>
> Does it ring anyone's bell?
>
> thanks.
>
> Hiroshi
>