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, 159 insertions, 0 deletions

diff --git a/drivers/gpu/host1x/intr.c b/drivers/gpu/host1x/intr.c
new file mode 100644
index 000000000..723297250
--- /dev/null
+++ b/drivers/gpu/host1x/intr.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Tegra host1x Interrupt Management
+ *
+ * Copyright (c) 2010-2021, NVIDIA Corporation.
+ */
+
+#include <linux/clk.h>
+#include <linux/interrupt.h>
+#include "dev.h"
+#include "fence.h"
+#include "intr.h"
+
+static void host1x_intr_add_fence_to_list(struct host1x_fence_list *list,
+					  struct host1x_syncpt_fence *fence)
+{
+	struct host1x_syncpt_fence *fence_in_list;
+
+	list_for_each_entry_reverse(fence_in_list, &list->list, list) {
+		if ((s32)(fence_in_list->threshold - fence->threshold) <= 0) {
+			/* Fence in list is before us, we can insert here */
+			list_add(&fence->list, &fence_in_list->list);
+			return;
+		}
+	}
+
+	/* Add as first in list */
+	list_add(&fence->list, &list->list);
+}
+
+static void host1x_intr_update_hw_state(struct host1x *host, struct host1x_syncpt *sp)
+{
+	struct host1x_syncpt_fence *fence;
+
+	if (!list_empty(&sp->fences.list)) {
+		fence = list_first_entry(&sp->fences.list, struct host1x_syncpt_fence, list);
+
+		host1x_hw_intr_set_syncpt_threshold(host, sp->id, fence->threshold);
+		host1x_hw_intr_enable_syncpt_intr(host, sp->id);
+	} else {
+		host1x_hw_intr_disable_syncpt_intr(host, sp->id);
+	}
+}
+
+void host1x_intr_add_fence_locked(struct host1x *host, struct host1x_syncpt_fence *fence)
+{
+	struct host1x_fence_list *fence_list = &fence->sp->fences;
+
+	INIT_LIST_HEAD(&fence->list);
+
+	host1x_intr_add_fence_to_list(fence_list, fence);
+	host1x_intr_update_hw_state(host, fence->sp);
+}
+
+bool host1x_intr_remove_fence(struct host1x *host, struct host1x_syncpt_fence *fence)
+{
+	struct host1x_fence_list *fence_list = &fence->sp->fences;
+	unsigned long irqflags;
+
+	spin_lock_irqsave(&fence_list->lock, irqflags);
+
+	if (list_empty(&fence->list)) {
+		spin_unlock_irqrestore(&fence_list->lock, irqflags);
+		return false;
+	}
+
+	list_del_init(&fence->list);
+	host1x_intr_update_hw_state(host, fence->sp);
+
+	spin_unlock_irqrestore(&fence_list->lock, irqflags);
+
+	return true;
+}
+
+void host1x_intr_handle_interrupt(struct host1x *host, unsigned int id)
+{
+	struct host1x_syncpt *sp = &host->syncpt[id];
+	struct host1x_syncpt_fence *fence, *tmp;
+	unsigned int value;
+
+	value = host1x_syncpt_load(sp);
+
+	spin_lock(&sp->fences.lock);
+
+	list_for_each_entry_safe(fence, tmp, &sp->fences.list, list) {
+		if (((value - fence->threshold) & 0x80000000U) != 0U) {
+			/* Fence is not yet expired, we are done */
+			break;
+		}
+
+		list_del_init(&fence->list);
+		host1x_fence_signal(fence);
+	}
+
+	/*
+	 * Re-enable interrupt if necessary. The ISR already disabled the interrupt,
+	 * so if no fences remain, no update is needed.
+	 */
+	if (!list_empty(&sp->fences.list))
+		host1x_intr_update_hw_state(host, sp);
+
+	spin_unlock(&sp->fences.lock);
+}
+
+int host1x_intr_init(struct host1x *host)
+{
+	struct host1x_intr_irq_data *irq_data;
+	unsigned int id;
+	int i, err;
+
+	for (id = 0; id < host1x_syncpt_nb_pts(host); ++id) {
+		struct host1x_syncpt *syncpt = &host->syncpt[id];
+
+		spin_lock_init(&syncpt->fences.lock);
+		INIT_LIST_HEAD(&syncpt->fences.list);
+	}
+
+	irq_data = devm_kcalloc(host->dev, host->num_syncpt_irqs, sizeof(irq_data[0]), GFP_KERNEL);
+	if (!irq_data)
+		return -ENOMEM;
+
+	host1x_hw_intr_disable_all_syncpt_intrs(host);
+
+	for (i = 0; i < host->num_syncpt_irqs; i++) {
+		irq_data[i].host = host;
+		irq_data[i].offset = i;
+
+		err = devm_request_irq(host->dev, host->syncpt_irqs[i],
+				       host->intr_op->isr, IRQF_SHARED,
+				       "host1x_syncpt", &irq_data[i]);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+void host1x_intr_deinit(struct host1x *host)
+{
+}
+
+void host1x_intr_start(struct host1x *host)
+{
+	u32 hz = clk_get_rate(host->clk);
+	int err;
+
+	mutex_lock(&host->intr_mutex);
+	err = host1x_hw_intr_init_host_sync(host, DIV_ROUND_UP(hz, 1000000));
+	if (err) {
+		mutex_unlock(&host->intr_mutex);
+		return;
+	}
+	mutex_unlock(&host->intr_mutex);
+}
+
+void host1x_intr_stop(struct host1x *host)
+{
+	host1x_hw_intr_disable_all_syncpt_intrs(host);
+}