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, 258 insertions, 0 deletions

diff --git a/drivers/clk/ti/gate.c b/drivers/clk/ti/gate.c
new file mode 100644
index 000000000..747412270
--- /dev/null
+++ b/drivers/clk/ti/gate.c
@@ -0,0 +1,258 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * OMAP gate clock support
+ *
+ * Copyright (C) 2013 Texas Instruments, Inc.
+ *
+ * Tero Kristo <t-kristo@ti.com>
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/clk/ti.h>
+
+#include "clock.h"
+
+#undef pr_fmt
+#define pr_fmt(fmt) "%s: " fmt, __func__
+
+static int omap36xx_gate_clk_enable_with_hsdiv_restore(struct clk_hw *clk);
+
+static const struct clk_ops omap_gate_clkdm_clk_ops = {
+	.init		= &omap2_init_clk_clkdm,
+	.enable		= &omap2_clkops_enable_clkdm,
+	.disable	= &omap2_clkops_disable_clkdm,
+	.restore_context = clk_gate_restore_context,
+};
+
+const struct clk_ops omap_gate_clk_ops = {
+	.init		= &omap2_init_clk_clkdm,
+	.enable		= &omap2_dflt_clk_enable,
+	.disable	= &omap2_dflt_clk_disable,
+	.is_enabled	= &omap2_dflt_clk_is_enabled,
+	.restore_context = clk_gate_restore_context,
+};
+
+static const struct clk_ops omap_gate_clk_hsdiv_restore_ops = {
+	.init		= &omap2_init_clk_clkdm,
+	.enable		= &omap36xx_gate_clk_enable_with_hsdiv_restore,
+	.disable	= &omap2_dflt_clk_disable,
+	.is_enabled	= &omap2_dflt_clk_is_enabled,
+	.restore_context = clk_gate_restore_context,
+};
+
+/**
+ * omap36xx_gate_clk_enable_with_hsdiv_restore - enable clocks suffering
+ *         from HSDivider PWRDN problem Implements Errata ID: i556.
+ * @hw: DPLL output struct clk_hw
+ *
+ * 3630 only: dpll3_m3_ck, dpll4_m2_ck, dpll4_m3_ck, dpll4_m4_ck,
+ * dpll4_m5_ck & dpll4_m6_ck dividers gets loaded with reset
+ * valueafter their respective PWRDN bits are set.  Any dummy write
+ * (Any other value different from the Read value) to the
+ * corresponding CM_CLKSEL register will refresh the dividers.
+ */
+static int omap36xx_gate_clk_enable_with_hsdiv_restore(struct clk_hw *hw)
+{
+	struct clk_omap_divider *parent;
+	struct clk_hw *parent_hw;
+	u32 dummy_v, orig_v;
+	int ret;
+
+	/* Clear PWRDN bit of HSDIVIDER */
+	ret = omap2_dflt_clk_enable(hw);
+
+	/* Parent is the x2 node, get parent of parent for the m2 div */
+	parent_hw = clk_hw_get_parent(clk_hw_get_parent(hw));
+	parent = to_clk_omap_divider(parent_hw);
+
+	/* Restore the dividers */
+	if (!ret) {
+		orig_v = ti_clk_ll_ops->clk_readl(&parent->reg);
+		dummy_v = orig_v;
+
+		/* Write any other value different from the Read value */
+		dummy_v ^= (1 << parent->shift);
+		ti_clk_ll_ops->clk_writel(dummy_v, &parent->reg);
+
+		/* Write the original divider */
+		ti_clk_ll_ops->clk_writel(orig_v, &parent->reg);
+	}
+
+	return ret;
+}
+
+static struct clk *_register_gate(struct device_node *node, const char *name,
+				  const char *parent_name, unsigned long flags,
+				  struct clk_omap_reg *reg, u8 bit_idx,
+				  u8 clk_gate_flags, const struct clk_ops *ops,
+				  const struct clk_hw_omap_ops *hw_ops)
+{
+	struct clk_init_data init = { NULL };
+	struct clk_hw_omap *clk_hw;
+	struct clk *clk;
+
+	clk_hw = kzalloc_obj(*clk_hw);
+	if (!clk_hw)
+		return ERR_PTR(-ENOMEM);
+
+	clk_hw->hw.init = &init;
+
+	init.name = name;
+	init.ops = ops;
+
+	memcpy(&clk_hw->enable_reg, reg, sizeof(*reg));
+	clk_hw->enable_bit = bit_idx;
+	clk_hw->ops = hw_ops;
+
+	clk_hw->flags = clk_gate_flags;
+
+	init.parent_names = &parent_name;
+	init.num_parents = 1;
+
+	init.flags = flags;
+
+	clk = of_ti_clk_register_omap_hw(node, &clk_hw->hw, name);
+
+	if (IS_ERR(clk))
+		kfree(clk_hw);
+
+	return clk;
+}
+
+static void __init _of_ti_gate_clk_setup(struct device_node *node,
+					 const struct clk_ops *ops,
+					 const struct clk_hw_omap_ops *hw_ops)
+{
+	struct clk *clk;
+	const char *parent_name;
+	struct clk_omap_reg reg;
+	const char *name;
+	u8 enable_bit = 0;
+	u32 flags = 0;
+	u8 clk_gate_flags = 0;
+
+	if (ops != &omap_gate_clkdm_clk_ops) {
+		if (ti_clk_get_reg_addr(node, 0, &reg))
+			return;
+
+		enable_bit = reg.bit;
+	}
+
+	if (of_clk_get_parent_count(node) != 1) {
+		pr_err("%pOFn must have 1 parent\n", node);
+		return;
+	}
+
+	parent_name = of_clk_get_parent_name(node, 0);
+
+	if (of_property_read_bool(node, "ti,set-rate-parent"))
+		flags |= CLK_SET_RATE_PARENT;
+
+	if (of_property_read_bool(node, "ti,set-bit-to-disable"))
+		clk_gate_flags |= INVERT_ENABLE;
+
+	name = ti_dt_clk_name(node);
+	clk = _register_gate(node, name, parent_name, flags, &reg,
+			     enable_bit, clk_gate_flags, ops, hw_ops);
+
+	if (!IS_ERR(clk))
+		of_clk_add_provider(node, of_clk_src_simple_get, clk);
+}
+
+static void __init
+_of_ti_composite_gate_clk_setup(struct device_node *node,
+				const struct clk_hw_omap_ops *hw_ops)
+{
+	struct clk_hw_omap *gate;
+
+	gate = kzalloc_obj(*gate);
+	if (!gate)
+		return;
+
+	if (ti_clk_get_reg_addr(node, 0, &gate->enable_reg))
+		goto cleanup;
+
+	gate->enable_bit = gate->enable_reg.bit;
+	gate->ops = hw_ops;
+
+	if (!ti_clk_add_component(node, &gate->hw, CLK_COMPONENT_TYPE_GATE))
+		return;
+
+cleanup:
+	kfree(gate);
+}
+
+static void __init
+of_ti_composite_no_wait_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_composite_gate_clk_setup(node, NULL);
+}
+CLK_OF_DECLARE(ti_composite_no_wait_gate_clk, "ti,composite-no-wait-gate-clock",
+	       of_ti_composite_no_wait_gate_clk_setup);
+
+#if defined(CONFIG_ARCH_OMAP2) || defined(CONFIG_ARCH_OMAP3)
+static void __init of_ti_composite_interface_clk_setup(struct device_node *node)
+{
+	_of_ti_composite_gate_clk_setup(node, &clkhwops_iclk_wait);
+}
+CLK_OF_DECLARE(ti_composite_interface_clk, "ti,composite-interface-clock",
+	       of_ti_composite_interface_clk_setup);
+#endif
+
+static void __init of_ti_composite_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_composite_gate_clk_setup(node, &clkhwops_wait);
+}
+CLK_OF_DECLARE(ti_composite_gate_clk, "ti,composite-gate-clock",
+	       of_ti_composite_gate_clk_setup);
+
+
+static void __init of_ti_clkdm_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clkdm_clk_ops, NULL);
+}
+CLK_OF_DECLARE(ti_clkdm_gate_clk, "ti,clkdm-gate-clock",
+	       of_ti_clkdm_gate_clk_setup);
+
+static void __init of_ti_hsdiv_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clk_hsdiv_restore_ops,
+			      &clkhwops_wait);
+}
+CLK_OF_DECLARE(ti_hsdiv_gate_clk, "ti,hsdiv-gate-clock",
+	       of_ti_hsdiv_gate_clk_setup);
+
+static void __init of_ti_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clk_ops, NULL);
+}
+CLK_OF_DECLARE(ti_gate_clk, "ti,gate-clock", of_ti_gate_clk_setup);
+
+static void __init of_ti_wait_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clk_ops, &clkhwops_wait);
+}
+CLK_OF_DECLARE(ti_wait_gate_clk, "ti,wait-gate-clock",
+	       of_ti_wait_gate_clk_setup);
+
+#ifdef CONFIG_ARCH_OMAP3
+static void __init of_ti_am35xx_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clk_ops,
+			      &clkhwops_am35xx_ipss_module_wait);
+}
+CLK_OF_DECLARE(ti_am35xx_gate_clk, "ti,am35xx-gate-clock",
+	       of_ti_am35xx_gate_clk_setup);
+
+static void __init of_ti_dss_gate_clk_setup(struct device_node *node)
+{
+	_of_ti_gate_clk_setup(node, &omap_gate_clk_ops,
+			      &clkhwops_omap3430es2_dss_usbhost_wait);
+}
+CLK_OF_DECLARE(ti_dss_gate_clk, "ti,dss-gate-clock",
+	       of_ti_dss_gate_clk_setup);
+#endif