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, 141 insertions, 0 deletions

diff --git a/tools/perf/ui/setup.c b/tools/perf/ui/setup.c
new file mode 100644
index 000000000..ff800047e
--- /dev/null
+++ b/tools/perf/ui/setup.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <dlfcn.h>
+#include <signal.h>
+#include <unistd.h>
+
+#include <subcmd/pager.h>
+#include "../util/debug.h"
+#include "../util/hist.h"
+#include "ui.h"
+
+struct mutex ui__lock;
+void *perf_gtk_handle;
+int use_browser = -1;
+
+#define PERF_GTK_DSO "libperf-gtk.so"
+
+#ifdef HAVE_GTK2_SUPPORT
+
+static int setup_gtk_browser(void)
+{
+	int (*perf_ui_init)(void);
+
+	if (perf_gtk_handle)
+		return 0;
+
+	perf_gtk_handle = dlopen(PERF_GTK_DSO, RTLD_LAZY);
+	if (perf_gtk_handle == NULL) {
+		char buf[PATH_MAX];
+		scnprintf(buf, sizeof(buf), "%s/%s", LIBDIR, PERF_GTK_DSO);
+		perf_gtk_handle = dlopen(buf, RTLD_LAZY);
+	}
+	if (perf_gtk_handle == NULL)
+		return -1;
+
+	perf_ui_init = dlsym(perf_gtk_handle, "perf_gtk__init");
+	if (perf_ui_init == NULL)
+		goto out_close;
+
+	if (perf_ui_init() == 0)
+		return 0;
+
+out_close:
+	dlclose(perf_gtk_handle);
+	return -1;
+}
+
+static void exit_gtk_browser(bool wait_for_ok)
+{
+	void (*perf_ui_exit)(bool);
+
+	if (perf_gtk_handle == NULL)
+		return;
+
+	perf_ui_exit = dlsym(perf_gtk_handle, "perf_gtk__exit");
+	if (perf_ui_exit == NULL)
+		goto out_close;
+
+	perf_ui_exit(wait_for_ok);
+
+out_close:
+	dlclose(perf_gtk_handle);
+
+	perf_gtk_handle = NULL;
+}
+#else
+static inline int setup_gtk_browser(void) { return -1; }
+static inline void exit_gtk_browser(bool wait_for_ok __maybe_unused) {}
+#endif
+
+int stdio__config_color(const struct option *opt __maybe_unused,
+			const char *mode, int unset __maybe_unused)
+{
+	perf_use_color_default = perf_config_colorbool("color.ui", mode, -1);
+	return 0;
+}
+
+void setup_browser(bool fallback_to_pager)
+{
+	mutex_init(&ui__lock);
+	if (use_browser < 2 && (!isatty(1) || dump_trace))
+		use_browser = 0;
+
+	/* default to TUI */
+	if (use_browser < 0)
+		use_browser = 1;
+
+	switch (use_browser) {
+	case 2:
+		if (setup_gtk_browser() == 0)
+			break;
+		printf("GTK browser requested but could not find %s\n",
+		       PERF_GTK_DSO);
+		sleep(1);
+		use_browser = 1;
+		/* fall through */
+	case 1:
+		if (ui__init() == 0)
+			break;
+		/* fall through */
+	default:
+		use_browser = 0;
+		if (fallback_to_pager)
+			setup_pager();
+		break;
+	}
+}
+
+void exit_browser(bool wait_for_ok)
+{
+	switch (use_browser) {
+	case 2:
+		exit_gtk_browser(wait_for_ok);
+		break;
+
+	case 1:
+		ui__exit(wait_for_ok);
+		break;
+
+	default:
+		break;
+	}
+	mutex_destroy(&ui__lock);
+}
+
+void pthread__block_sigwinch(void)
+{
+	sigset_t set;
+
+	sigemptyset(&set);
+	sigaddset(&set, SIGWINCH);
+	pthread_sigmask(SIG_BLOCK, &set, NULL);
+}
+
+void pthread__unblock_sigwinch(void)
+{
+	sigset_t set;
+
+	sigemptyset(&set);
+	sigaddset(&set, SIGWINCH);
+	pthread_sigmask(SIG_UNBLOCK, &set, NULL);
+}