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>

1 files changed, 125 insertions, 0 deletions

diff --git a/tools/perf/util/mutex.c b/tools/perf/util/mutex.c
new file mode 100644
index 000000000..7aa1f3f55
--- /dev/null
+++ b/tools/perf/util/mutex.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "mutex.h"
+
+#include "debug.h"
+#include <linux/string.h>
+#include <errno.h>
+
+static void check_err(const char *fn, int err)
+{
+	char sbuf[STRERR_BUFSIZE];
+
+	if (err == 0)
+		return;
+
+	pr_err("%s error: '%s'\n", fn, str_error_r(err, sbuf, sizeof(sbuf)));
+}
+
+#define CHECK_ERR(err) check_err(__func__, err)
+
+static void __mutex_init(struct mutex *mtx, bool pshared, bool recursive)
+{
+	pthread_mutexattr_t attr;
+
+	CHECK_ERR(pthread_mutexattr_init(&attr));
+
+#ifndef NDEBUG
+	/* In normal builds enable error checking, such as recursive usage. */
+	CHECK_ERR(pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK));
+#endif
+	if (recursive)
+		CHECK_ERR(pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE));
+	if (pshared)
+		CHECK_ERR(pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED));
+	CHECK_ERR(pthread_mutex_init(&mtx->lock, &attr));
+	CHECK_ERR(pthread_mutexattr_destroy(&attr));
+}
+
+void mutex_init(struct mutex *mtx)
+{
+	__mutex_init(mtx, /*pshared=*/false, /*recursive=*/false);
+}
+
+void mutex_init_pshared(struct mutex *mtx)
+{
+	__mutex_init(mtx, /*pshared=*/true, /*recursive=*/false);
+}
+
+void mutex_init_recursive(struct mutex *mtx)
+{
+	__mutex_init(mtx, /*pshared=*/false, /*recursive=*/true);
+}
+
+void mutex_destroy(struct mutex *mtx)
+{
+	CHECK_ERR(pthread_mutex_destroy(&mtx->lock));
+}
+
+void mutex_lock(struct mutex *mtx)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+	CHECK_ERR(pthread_mutex_lock(&mtx->lock));
+}
+
+void mutex_unlock(struct mutex *mtx)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+	CHECK_ERR(pthread_mutex_unlock(&mtx->lock));
+}
+
+bool mutex_trylock(struct mutex *mtx)
+{
+	int ret = pthread_mutex_trylock(&mtx->lock);
+
+	if (ret == 0)
+		return true; /* Lock acquired. */
+
+	if (ret == EBUSY)
+		return false; /* Lock busy. */
+
+	/* Print error. */
+	CHECK_ERR(ret);
+	return false;
+}
+
+static void __cond_init(struct cond *cnd, bool pshared)
+{
+	pthread_condattr_t attr;
+
+	CHECK_ERR(pthread_condattr_init(&attr));
+	if (pshared)
+		CHECK_ERR(pthread_condattr_setpshared(&attr, PTHREAD_PROCESS_SHARED));
+
+	CHECK_ERR(pthread_cond_init(&cnd->cond, &attr));
+	CHECK_ERR(pthread_condattr_destroy(&attr));
+}
+
+void cond_init(struct cond *cnd)
+{
+	__cond_init(cnd, /*pshared=*/false);
+}
+
+void cond_init_pshared(struct cond *cnd)
+{
+	__cond_init(cnd, /*pshared=*/true);
+}
+
+void cond_destroy(struct cond *cnd)
+{
+	CHECK_ERR(pthread_cond_destroy(&cnd->cond));
+}
+
+void cond_wait(struct cond *cnd, struct mutex *mtx)
+{
+	CHECK_ERR(pthread_cond_wait(&cnd->cond, &mtx->lock));
+}
+
+void cond_signal(struct cond *cnd)
+{
+	CHECK_ERR(pthread_cond_signal(&cnd->cond));
+}
+
+void cond_broadcast(struct cond *cnd)
+{
+	CHECK_ERR(pthread_cond_broadcast(&cnd->cond));
+}