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Diffstat (limited to 'gdb/doc/gdbint.texinfo')
| -rw-r--r-- | gdb/doc/gdbint.texinfo | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/gdb/doc/gdbint.texinfo b/gdb/doc/gdbint.texinfo index f7d7936..a81cc9b 100644 --- a/gdb/doc/gdbint.texinfo +++ b/gdb/doc/gdbint.texinfo @@ -231,6 +231,36 @@ they use. A frame is a construct that @value{GDBN} uses to keep track of calling and called functions. +@cindex frame, unwind +@value{GDBN}'s current frame model is the result of an incremental +cleanup of working code, not a fresh design, so it's a little weird. + +The natural model would have a frame object, with methods that read +and write that frame's registers. Reading or writing the youngest +frame's registers would simply read or write the processor's current +registers, since the youngest frame is running directly on the +processor. Older frames might have some registers saved on the stack +by younger frames, so accessing the older frames' registers would do a +mix of memory accesses and register accesses, as appropriate. + +@findex frame_register_unwind +Instead, @value{GDBN}'s model is that you find a frame's registers by +``unwinding'' them from the next younger frame. That is, to access +the registers of frame #1 (the next-to-youngest frame), you actually +apply @code{frame_register_unwind} to frame #0 (the youngest frame). +But then the obvious question is: how do you access the registers of +the youngest frame itself? How do you ``unwind'' them when they're +not wound up? + +@cindex sentinel frame +@findex get_frame_type +@vindex SENTINEL_FRAME +To answer this question, GDB has the @dfn{sentinel} frame, the +``-1st'' frame. Unwinding registers from the sentinel frame gives you +the current values of the youngest real frame's registers. If @var{f} +is a sentinel frame, then @code{get_frame_type (@var{f}) == +SENTINEL_FRAME}. + @findex create_new_frame @vindex FRAME_FP @code{FRAME_FP} in the machine description has no meaning to the |