[RFC PATCH v2 11/14] selftests/kcov_dataflow: add eight_args_rust test module

[Yunseong Kim <yunseong.kim@est.tech>]

Rust module exercising 1-8 argument functions plus struct pointer.
Verifies register-passed (1-6) and stack-passed (7-8) arguments.

Test:

  make LLVM=1 CC=clang RUSTC=$RUSTC RUST_LIB_SRC=$RUST_LIB_SRC \
    M=tools/testing/selftests/kcov_dataflow/eight_args_rust modules
  vng --user root --exec \
    "python3 tools/testing/selftests/kcov_dataflow/trigger-view.py \
      eight_args_rust -C 8 --ko \
      tools/testing/selftests/kcov_dataflow/eight_args_rust/eight_args_rust.ko"

Result:

  ksys_write(0x0, 0x1)
    fdget_pos(0x4)
    0xffff891481d2bc00 = fdget_pos()
  0x0 = vfs_write()
  vfs_write(0x0, 0x1, 0x0)
  0x0 = _RNvCs3p16QzTwthP_15eight_args_rust13write_handler [eight_args_rust]()
  _RNvCs3p16QzTwthP_15eight_args_rust13write_handler [eight_args_rust](0x0, 0x1, 0x0)
    rdf_func2 [eight_args_rust](0x11, 0x22)
    0x33 = rdf_func2 [eight_args_rust]()
    rdf_func3 [eight_args_rust](0x11, 0x22, 0x33)
    0x66 = rdf_func3 [eight_args_rust]()
    rdf_func4 [eight_args_rust](0x11, 0x22, 0x33, 0x44)
    0xaa = rdf_func4 [eight_args_rust]()
    rdf_func5 [eight_args_rust](0x11, 0x22, 0x33, 0x44, 0x55)
    0xff = rdf_func5 [eight_args_rust]()
    rdf_func6 [eight_args_rust](0x11, 0x22, 0x33, 0x44, 0x55, 0x66)
    0x165 = rdf_func6 [eight_args_rust]()
    rdf_func7 [eight_args_rust](0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77)
    0x1dc = rdf_func7 [eight_args_rust]()
    rdf_func8 [eight_args_rust](0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88)
    0x264 = rdf_func8 [eight_args_rust]()
    rdf_func_struct [eight_args_rust](0xaaaa)
    0x16665 = rdf_func_struct [eight_args_rust]()
  0x1 = _RNvCs3p16QzTwthP_15eight_args_rust13write_handler [eight_args_rust]()
  0x1 = vfs_write()
  0x1 = ksys_write()
  0x1 = __x64_sys_write()
  0x0 = fpregs_assert_state_consistent()
  0xba5748 = __x64_sys_close()
  file_close_fd(0x4)
  0x0 = file_close_fd()
  0x0 = filp_flush()

Cc: Alexander Potapenko <glider@google.com>
Assisted-by: Claude:claude-opus-4-6 [kiro-chat]
Link: https://github.com/yskzalloc/kcov-dataflow/actions
Signed-off-by: Yunseong Kim <yunseong.kim@est.tech>
---
 tools/testing/selftests/kcov_dataflow/README.rst   |   7 +
 .../kcov_dataflow/eight_args_rust/Makefile         |   3 +
 .../eight_args_rust/eight_args_rust.rs             | 143 +++++++++++++++++++++
 .../selftests/kcov_dataflow/run_eight_args_rust.sh |  35 +++++
 4 files changed, 188 insertions(+)

diff --git a/tools/testing/selftests/kcov_dataflow/README.rst b/tools/testing/selftests/kcov_dataflow/README.rst
index e93b4e573504..61a41f3bd596 100644
--- a/tools/testing/selftests/kcov_dataflow/README.rst
+++ b/tools/testing/selftests/kcov_dataflow/README.rst
@@ -41,3 +41,10 @@ eight_args_c/
 
         make LLVM=1 CC=clang M=tools/testing/selftests/kcov_dataflow/eight_args_c modules
         python3 trigger-view.py eight_args_c
+
+eight_args_rust/
+    Rust equivalent of eight_args_c. Captures arguments at -O2 where
+    drgn/vmcore cannot. Requires CONFIG_RUST::
+
+        make LLVM=1 CC=clang M=tools/testing/selftests/kcov_dataflow/eight_args_rust modules
+        python3 trigger-view.py eight_args_rust
diff --git a/tools/testing/selftests/kcov_dataflow/eight_args_rust/Makefile b/tools/testing/selftests/kcov_dataflow/eight_args_rust/Makefile
new file mode 100644
index 000000000000..c1e9ea2c5622
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/eight_args_rust/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-m := eight_args_rust.o
+KCOV_DATAFLOW_eight_args_rust.o := y
diff --git a/tools/testing/selftests/kcov_dataflow/eight_args_rust/eight_args_rust.rs b/tools/testing/selftests/kcov_dataflow/eight_args_rust/eight_args_rust.rs
new file mode 100644
index 000000000000..3026265cda97
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/eight_args_rust/eight_args_rust.rs
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Verify kcov_dataflow captures 1-8 argument Rust functions at -O2.
+//!
+//! This is the Rust equivalent of eight_args_c. Since rustc elides DWARF
+//! variable locations at -O2, drgn/vmcore cannot observe these arguments.
+//! kcov_dataflow captures them via the post-compilation pipeline.
+//!
+//! Write to /sys/kernel/debug/kcov_dataflow_test/trigger_rust to invoke.
+
+#![allow(missing_docs)]
+
+use kernel::prelude::*;
+use kernel::c_str;
+
+module! {
+    type: EightArgsRust,
+    name: "eight_args_rust",
+    authors: ["kcov-dataflow"],
+    description: "1-8 arg Rust verification for kcov_dataflow",
+    license: "GPL",
+}
+
+#[repr(C)]
+pub struct Pair {
+    pub x: u32,
+    pub y: u32,
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func1(a1: u64) -> u64 { a1 }
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func2(a1: u64, a2: u64) -> u64 { a1 + a2 }
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func3(a1: u64, a2: u64, a3: u64) -> u64 {
+    a1 + a2 + a3
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func4(a1: u64, a2: u64, a3: u64, a4: u64) -> u64 {
+    a1 + a2 + a3 + a4
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func5(a1: u64, a2: u64, a3: u64, a4: u64, a5: u64) -> u64 {
+    a1 + a2 + a3 + a4 + a5
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func6(
+    a1: u64, a2: u64, a3: u64, a4: u64, a5: u64, a6: u64,
+) -> u64 {
+    a1 + a2 + a3 + a4 + a5 + a6
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func7(
+    a1: u64, a2: u64, a3: u64, a4: u64, a5: u64, a6: u64, a7: u64,
+) -> u64 {
+    a1 + a2 + a3 + a4 + a5 + a6 + a7
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func8(
+    a1: u64, a2: u64, a3: u64, a4: u64, a5: u64, a6: u64, a7: u64, a8: u64,
+) -> u64 {
+    a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8
+}
+
+#[no_mangle]
+#[inline(never)]
+pub extern "C" fn rdf_func_struct(p: *const Pair) -> u64 {
+    unsafe { (*p).x as u64 + (*p).y as u64 }
+}
+
+unsafe extern "C" fn write_handler(
+    _file: *mut kernel::bindings::file,
+    _buf: *const core::ffi::c_char,
+    count: usize,
+    _ppos: *mut kernel::bindings::loff_t,
+) -> kernel::ffi::c_long {
+    let p = Pair { x: 0xAAAA, y: 0xBBBB };
+
+    let mut sum: u64 = 0;
+    sum = sum.wrapping_add(rdf_func1(0x11));
+    sum = sum.wrapping_add(rdf_func2(0x11, 0x22));
+    sum = sum.wrapping_add(rdf_func3(0x11, 0x22, 0x33));
+    sum = sum.wrapping_add(rdf_func4(0x11, 0x22, 0x33, 0x44));
+    sum = sum.wrapping_add(rdf_func5(0x11, 0x22, 0x33, 0x44, 0x55));
+    sum = sum.wrapping_add(rdf_func6(0x11, 0x22, 0x33, 0x44, 0x55, 0x66));
+    sum = sum.wrapping_add(rdf_func7(0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77));
+    sum = sum.wrapping_add(rdf_func8(0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88));
+    sum = sum.wrapping_add(rdf_func_struct(&p as *const Pair));
+    core::hint::black_box(sum);
+
+    count as kernel::ffi::c_long
+}
+
+#[repr(transparent)]
+struct SyncFops(kernel::bindings::file_operations);
+unsafe impl Sync for SyncFops {}
+
+static FOPS: SyncFops = SyncFops(kernel::bindings::file_operations {
+    write: Some(unsafe { core::mem::transmute(write_handler as *const ()) }),
+    ..unsafe { core::mem::zeroed() }
+});
+
+struct EightArgsRust {
+    d: *mut kernel::bindings::dentry,
+}
+
+impl kernel::Module for EightArgsRust {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        let d = unsafe {
+            kernel::bindings::debugfs_create_file_unsafe(
+                c_str!("trigger_rust").as_char_ptr(),
+                0o222,
+                core::ptr::null_mut(),
+                core::ptr::null_mut(),
+                &FOPS.0,
+            )
+        };
+        Ok(Self { d })
+    }
+}
+
+impl Drop for EightArgsRust {
+    fn drop(&mut self) {
+        unsafe { kernel::bindings::debugfs_remove(self.d) };
+    }
+}
+
+unsafe impl Send for EightArgsRust {}
+unsafe impl Sync for EightArgsRust {}
diff --git a/tools/testing/selftests/kcov_dataflow/run_eight_args_rust.sh b/tools/testing/selftests/kcov_dataflow/run_eight_args_rust.sh
new file mode 100755
index 000000000000..c5f11866e19d
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/run_eight_args_rust.sh
@@ -0,0 +1,35 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Test eight_args_rust module capture via kcov_dataflow
+DIR="$(dirname "$0")"
+KO="$DIR/eight_args_rust/eight_args_rust.ko"
+
+if [ ! -f "$KO" ]; then
+	echo "SKIP: $KO not found"
+	echo "Build: make LLVM=1 CC=clang RUSTC=\$RUSTC M=...eight_args_rust modules""
+	exit 4  # kselftest SKIP
+fi
+
+if [ ! -e /sys/kernel/debug/kcov_dataflow ]; then
+	echo "SKIP: kcov_dataflow not available"
+	exit 4
+fi
+
+OUTPUT=$(python3 "$DIR/trigger-view.py" eight_args_rust --ko "$KO" --raw 2>&1)
+RC=$?
+
+if [ $RC -ne 0 ]; then
+	echo "FAIL: trigger-and-view exited with $RC"
+	echo "$OUTPUT"
+	exit 1
+fi
+
+RECORDS=$(echo "$OUTPUT" | grep -c "^\[ENTRY\]\|^\[RET")
+if [ "$RECORDS" -gt 0 ]; then
+	echo "PASS: captured $RECORDS records from eight_args_rust"
+	exit 0
+else
+	echo "FAIL: no records captured"
+	echo "$OUTPUT"
+	exit 1
+fi

-- 
2.43.0