tracing/probes: Eliminate recursion in parse_probe_arg()

To avoid potential stack overflows on limited kernel stacks, convert
parse_probe_arg() from a recursive function into a loop-based
implementation with a simple local state stack.

Since recursion is eliminated using a loop with a fixed-size
stack in the context, this restricts the dereference nesting
depth. The maximum nesting depth of dereferences is now restricted
to the same limit as typecasts (TRACEPROBE_MAX_NESTED_LEVEL, which
is 8) and reports the same TOO_MANY_NESTED error. Update ftrace
selftests to reflect this restriction and simplify the checks.

Note that this change slightly alters the behavior of nested
dereferencing in fetcharg. Previously, dereferencing without BTF
allowed for up to 14 levels of nesting, whereas dereferencing
with BTF was limited to 3 levels. With this change, the nesting
depth is now limited to 8 levels in both cases.

Link: https://lore.kernel.org/all/178399141396.27810.5390060618628718661.stgit@devnote2/

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

0 files changed, 0 insertions, 0 deletions