Use exact remote reads for interpreter state, thread state, and
interpreter frame structs instead of pulling full remote pages into the
profiler page cache. This matches the core change from
python/cpython#149585.
The profiler clears the page cache between samples, so live entries are
always packed at the front. Track the live count and only clear/search
that prefix instead of scanning all 1024 slots on the hot path.
Use the frame cache to predict the next thread state and top frame
address, then batch interpreter/thread/frame reads with process_vm_readv
when profiling a Linux target. Reuse prefetched frame buffers in the
frame walker when the prediction is valid.
Cache the last FrameInfo tuple per code object/instruction offset, reuse
cached thread id objects, and append cached parent frames directly on
full frame-cache hits. This cuts Python allocation churn in the
steady-state profiler path.
Treat the debug offset tables read from a target process as untrusted input
and validate them before the unwinder uses any reported sizes or offsets.
Add a shared validator in debug_offsets_validation.h and run it once when
_Py_DebugOffsets is loaded and once when AsyncioDebug is loaded. The checks
cover section sizes used for fixed local buffers and every offset that is
later dereferenced against a local buffer or local object view. This keeps
the bounds checks out of the sampling hot path while rejecting malformed
tables up front.
This PR implements frame caching in the RemoteUnwinder class to significantly reduce memory reads when profiling remote processes with deep call stacks.
When cache_frames=True, the unwinder stores the frame chain from each sample and reuses unchanged portions in subsequent samples. Since most profiling samples capture similar call stacks (especially the parent frames), this optimization avoids repeatedly reading the same frame data from the target process.
The implementation adds a last_profiled_frame field to the thread state that tracks where the previous sample stopped. On the next sample, if the current frame chain reaches this marker, the cached frames from that point onward are reused instead of being re-read from remote memory.
The sampling profiler now enables frame caching by default.
