[External] : Re: Where does VMError::print_native_stack and os::get_sender_for_C_frame load/use the frame pointer?

[dean.long at oracle.com]

Using fr->link() in get_sender_for_C_frame() gives the wrong answer 
because it refers to the current frame, not the sender frame. There is 
no frame::sender_fp() because the information we need could be anywhere 
in the frame or even nowhere in the frame. This is what the comment 
about StackWalk() API is hinting at. Even debuggers can have trouble 
giving an accurate stack trace if external debug information is missing 
and frames do not contain the needed information themselves.

dl

On 7/10/24 10:52 PM, Julian Waters wrote:
> Hi Dean,
>
> I eventually did find frame::link(), but ultimately it didn't seem to help as VMError::print_native_stack still doesn't work properly on Windows. It seems as though frame::link() calls addr_at on x86, which in turn calls frame::fp(), which returns _fp. I think whatever sets _fp for VMError::print_native_stack is the missing link here, but unfortunately I don't know where it's set
>
> The code that I tried on Windows x64 is attached below
>
> best regards,
> Julian
>
> // VC++ does not save frame pointer on stack in optimized build. It
> // can be turned off by -Oy-. If we really want to walk C frames,
> // we can use the StackWalk() API.
> frame os::get_sender_for_C_frame(frame* fr) {
> #ifdef __GNUC__
>    return frame(fr->sender_sp(), fr->link(), fr->sender_pc());
> #elif defined(_MSC_VER)
>    ShouldNotReachHere();
>    return frame();
> #endif
> }
>
> frame os::current_frame() {
> #ifdef __GNUC__
>    frame f(reinterpret_cast<intptr_t*>(os::current_stack_pointer()),
>            reinterpret_cast<intptr_t*>(__builtin_frame_address(1)),
>            CAST_FROM_FN_PTR(address, &os::current_frame));
>    if (os::is_first_C_frame(&f)) {
>      // stack is not walkable
>      return frame();
>    } else {
>      return os::get_sender_for_C_frame(&f);
>    }
> #elif defined(_MSC_VER)
>    return frame();  // cannot walk Windows frames this way.  See os::get_native_stack
>                     // and os::platform_print_native_stack
> #endif
> }
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