[PATCH 25/25] doc: add BPF validate debug to programmer's guide

[Marat Khalili <marat.khalili@huawei.com>]

Document the new gdb-like validation debugger API, outlining how it can
be used to set breakpoints and inspect register states during
validation.

Highlight its primary use case: writing robust tests for the eBPF
verifier using the harness in app/test/test_bpf_validate.c.

Signed-off-by: Marat Khalili <marat.khalili@huawei.com>
---
 doc/guides/prog_guide/bpf_lib.rst | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/doc/guides/prog_guide/bpf_lib.rst b/doc/guides/prog_guide/bpf_lib.rst
index df3782508829..08ea1876875a 100644
--- a/doc/guides/prog_guide/bpf_lib.rst
+++ b/doc/guides/prog_guide/bpf_lib.rst
@@ -118,6 +118,37 @@ For example, ``(BPF_IND | BPF_W | BPF_LD)`` means:
 and ``R1-R5`` were scratched.
 
 
+Validation Debugger
+-------------------
+
+The DPDK BPF library includes a validation debugger API designed primarily for
+writing comprehensive unit tests for the eBPF verifier. It allows developers
+to introspect the abstract interpretation process step-by-step to guarantee
+that the verifier correctly models the semantics of eBPF instructions.
+
+The debugger operates using a gdb-like approach:
+
+1.  **Initialization:** Create a debug session using
+    ``rte_bpf_validate_debug_create()`` and pass it to the loader via the
+    ``debug`` field in ``struct rte_bpf_prm_ex``.
+2.  **Breakpoints and Catchpoints:** Before loading, use
+    ``rte_bpf_validate_debug_break()`` or ``rte_bpf_validate_debug_catch()``
+    to register callback functions that trigger at specific instruction indices
+    (program counters) or upon specific validation events.
+3.  **State Introspection:** Within the callbacks, the API provides functions
+    like ``rte_bpf_validate_debug_can_access()``,
+    ``rte_bpf_validate_debug_may_jump()``, and various formatting functions
+    to safely inspect the verifier's internal belief about register bounds
+    and memory states at that specific execution point.
+
+When adding a test for a new eBPF instruction or fixing a validator bug,
+developers should utilize the harness provided in
+``app/test/test_bpf_validate.c``. This harness encapsulates the debugger API,
+allowing you to define the expected abstract domains (signed and unsigned
+intervals) for registers before and after a tested instruction, generating
+the necessary eBPF bytecode and breakpoints automatically.
+
+
 Not currently supported eBPF features
 -------------------------------------
 
-- 
2.43.0