kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

10 files changed, 250 insertions, 0 deletions

diff --git a/tools/testing/selftests/verification/.gitignore b/tools/testing/selftests/verification/.gitignore
new file mode 100644
index 000000000..2659417cb
--- /dev/null
+++ b/tools/testing/selftests/verification/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+logs
diff --git a/tools/testing/selftests/verification/Makefile b/tools/testing/selftests/verification/Makefile
new file mode 100644
index 000000000..aa8790c22
--- /dev/null
+++ b/tools/testing/selftests/verification/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+all:
+
+TEST_PROGS := verificationtest-ktap
+TEST_FILES := test.d settings
+EXTRA_CLEAN := $(OUTPUT)/logs/*
+
+include ../lib.mk
diff --git a/tools/testing/selftests/verification/config b/tools/testing/selftests/verification/config
new file mode 100644
index 000000000..43072c1c3
--- /dev/null
+++ b/tools/testing/selftests/verification/config
@@ -0,0 +1 @@
+CONFIG_RV=y
diff --git a/tools/testing/selftests/verification/settings b/tools/testing/selftests/verification/settings
new file mode 100644
index 000000000..e7b941753
--- /dev/null
+++ b/tools/testing/selftests/verification/settings
@@ -0,0 +1 @@
+timeout=0
diff --git a/tools/testing/selftests/verification/test.d/functions b/tools/testing/selftests/verification/test.d/functions
new file mode 100644
index 000000000..ec36a092f
--- /dev/null
+++ b/tools/testing/selftests/verification/test.d/functions
@@ -0,0 +1,39 @@
+check_requires() { # Check required files, monitors and reactors
+	for i in "$@" ; do
+		p=${i%:program}
+		m=${i%:monitor}
+		r=${i%:reactor}
+		if [ $p != $i ]; then
+			if ! which $p ; then
+				echo "Required program $p is not found."
+				exit_unresolved
+			fi
+		elif [ $m != $i ]; then
+			if ! grep -wq $m available_monitors ; then
+				echo "Required monitor $m is not configured."
+				exit_unsupported
+			fi
+		elif [ $r != $i ]; then
+			if ! grep -wq $r available_reactors ; then
+				echo "Required reactor $r is not configured."
+				exit_unsupported
+			fi
+		elif [ ! -e $i ]; then
+			echo "Required feature interface $i doesn't exist."
+			exit_unsupported
+		fi
+	done
+}
+
+initialize_system() { # Reset RV to initial-state
+	echo > enabled_monitors
+	for m in monitors/*; do
+		echo nop > $m/reactors || true
+	done
+	echo 1 > monitoring_on
+	echo 1 > reacting_on || true
+}
+
+finish_system() {
+	initialize_system
+}
diff --git a/tools/testing/selftests/verification/test.d/rv_monitor_enable_disable.tc b/tools/testing/selftests/verification/test.d/rv_monitor_enable_disable.tc
new file mode 100644
index 000000000..f29236def
--- /dev/null
+++ b/tools/testing/selftests/verification/test.d/rv_monitor_enable_disable.tc
@@ -0,0 +1,75 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# description: Test monitor enable/disable
+
+test_simple_monitor() {
+    local monitor="$1"
+    local prefix="$2" # nested monitors
+
+    echo 1 > "monitors/$prefix$monitor/enable"
+    grep -q "$monitor$" enabled_monitors
+
+    echo 0 > "monitors/$prefix$monitor/enable"
+    ! grep -q "$monitor$" enabled_monitors
+
+    echo "$monitor" >> enabled_monitors
+    grep -q 1 "monitors/$prefix$monitor/enable"
+
+    echo "!$monitor" >> enabled_monitors
+    grep -q 0 "monitors/$prefix$monitor/enable"
+}
+
+test_container_monitor() {
+    local monitor="$1"
+	local nested
+
+    echo 1 > "monitors/$monitor/enable"
+    grep -q "^$monitor$" enabled_monitors
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+        grep -q "^$monitor:$nested$" enabled_monitors
+    done
+	test -n "$nested"
+
+    echo 0 > "monitors/$monitor/enable"
+    ! grep -q "^$monitor$" enabled_monitors
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+        ! grep -q "^$monitor:$nested$" enabled_monitors
+    done
+
+    echo "$monitor" >> enabled_monitors
+    grep -q 1 "monitors/$monitor/enable"
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+        grep -q "^$monitor:$nested$" enabled_monitors
+    done
+
+    echo "!$monitor" >> enabled_monitors
+    grep -q 0 "monitors/$monitor/enable"
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+		test_simple_monitor "$nested" "$monitor/"
+    done
+}
+
+for monitor_dir in monitors/*; do
+    monitor=$(basename "$monitor_dir")
+
+    if find "$monitor_dir" -mindepth 1 -type d | grep -q .; then
+        test_container_monitor "$monitor"
+    else
+        test_simple_monitor "$monitor"
+    fi
+done
+
+! echo non_existent_monitor > enabled_monitors
+! grep -q "^non_existent_monitor$" enabled_monitors
diff --git a/tools/testing/selftests/verification/test.d/rv_monitor_reactor.tc b/tools/testing/selftests/verification/test.d/rv_monitor_reactor.tc
new file mode 100644
index 000000000..2958bf849
--- /dev/null
+++ b/tools/testing/selftests/verification/test.d/rv_monitor_reactor.tc
@@ -0,0 +1,68 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# description: Test monitor reactor setting
+# requires: available_reactors
+
+test_monitor_reactor() {
+    local monitor="$1"
+    local prefix="$2" # nested monitors
+
+    while read -r reactor; do
+        [ "$reactor" = nop ] && continue
+
+        echo "$reactor" > "monitors/$prefix$monitor/reactors"
+        grep -q "\\[$reactor\\]" "monitors/$prefix$monitor/reactors"
+    done < available_reactors
+
+    echo nop > "monitors/$prefix$monitor/reactors"
+    grep -q "\\[nop\\]" "monitors/$prefix$monitor/reactors"
+}
+
+test_container_monitor() {
+    local monitor="$1"
+	local nested
+
+    while read -r reactor; do
+        [ "$reactor" = nop ] && continue
+
+        echo "$reactor" > "monitors/$monitor/reactors"
+        grep -q "\\[$reactor\\]" "monitors/$monitor/reactors"
+
+        for nested_dir in "monitors/$monitor"/*; do
+            [ -d "$nested_dir" ] || continue
+            nested=$(basename "$nested_dir")
+            grep -q "\\[$reactor\\]" "monitors/$monitor/$nested/reactors"
+        done
+    done < available_reactors
+	test -n "$nested"
+
+    echo nop > "monitors/$monitor/reactors"
+    grep -q "\\[nop\\]" "monitors/$monitor/reactors"
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+        grep -q "\\[nop\\]" "monitors/$monitor/$nested/reactors"
+    done
+
+    for nested_dir in "monitors/$monitor"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+        test_monitor_reactor "$nested" "$monitor/"
+    done
+}
+
+for monitor_dir in monitors/*; do
+    monitor=$(basename "$monitor_dir")
+
+    if find "$monitor_dir" -mindepth 1 -type d | grep -q .; then
+        test_container_monitor "$monitor"
+    else
+        test_monitor_reactor "$monitor"
+    fi
+done
+
+monitor=$(ls /sys/kernel/tracing/rv/monitors -1 | head -n 1)
+test -f "monitors/$monitor/reactors"
+! echo non_existent_reactor > "monitors/$monitor/reactors"
+! grep -q "\\[non_existent_reactor\\]" "monitors/$monitor/reactors"
diff --git a/tools/testing/selftests/verification/test.d/rv_monitors_available.tc b/tools/testing/selftests/verification/test.d/rv_monitors_available.tc
new file mode 100644
index 000000000..e6a4a1410
--- /dev/null
+++ b/tools/testing/selftests/verification/test.d/rv_monitors_available.tc
@@ -0,0 +1,18 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# description: Check available monitors
+
+for monitor_dir in monitors/*; do
+    monitor=$(basename "$monitor_dir")
+
+    grep -q "^$monitor$" available_monitors
+    grep -q . "$monitor_dir"/desc
+
+    for nested_dir in "$monitor_dir"/*; do
+        [ -d "$nested_dir" ] || continue
+        nested=$(basename "$nested_dir")
+
+        grep -q "^$monitor:$nested$" available_monitors
+		grep -q . "$nested_dir"/desc
+    done
+done
diff --git a/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc b/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc
new file mode 100644
index 000000000..5a59432b1
--- /dev/null
+++ b/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc
@@ -0,0 +1,30 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# description: Test wwnr monitor with printk reactor
+# requires: available_reactors wwnr:monitor printk:reactor stress-ng:program
+
+load() { # returns true if there was a reaction
+	local lines_before num
+	num=$((($(nproc) + 1) / 2))
+	lines_before=$(dmesg | wc -l)
+	stress-ng --cpu-sched "$num" --timer "$num" -t 5 -q
+	dmesg | tail -n $((lines_before + 1)) | grep -q "rv: monitor wwnr does not allow event"
+}
+
+echo 1 > monitors/wwnr/enable
+echo printk > monitors/wwnr/reactors
+
+load
+
+echo 0 > monitoring_on
+! load
+echo 1 > monitoring_on
+
+load
+
+echo 0 > reacting_on
+! load
+echo 1 > reacting_on
+
+echo nop > monitors/wwnr/reactors
+echo 0 > monitors/wwnr/enable
diff --git a/tools/testing/selftests/verification/verificationtest-ktap b/tools/testing/selftests/verification/verificationtest-ktap
new file mode 100755
index 000000000..18f7fe324
--- /dev/null
+++ b/tools/testing/selftests/verification/verificationtest-ktap
@@ -0,0 +1,8 @@
+#!/bin/sh -e
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# ftracetest-ktap: Wrapper to integrate ftracetest with the kselftest runner
+#
+# Copyright (C) Arm Ltd., 2023
+
+../ftrace/ftracetest -K -v --rv ../verification