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>

2 files changed, 241 insertions, 0 deletions

diff --git a/drivers/clk/axis/Makefile b/drivers/clk/axis/Makefile
new file mode 100644
index 000000000..a6a9bbe7f
--- /dev/null
+++ b/drivers/clk/axis/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_MACH_ARTPEC6)	+= clk-artpec6.o
diff --git a/drivers/clk/axis/clk-artpec6.c b/drivers/clk/axis/clk-artpec6.c
new file mode 100644
index 000000000..a6f149962
--- /dev/null
+++ b/drivers/clk/axis/clk-artpec6.c
@@ -0,0 +1,239 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ARTPEC-6 clock initialization
+ *
+ * Copyright 2015-2016 Axis Communications AB.
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <dt-bindings/clock/axis,artpec6-clkctrl.h>
+
+#define NUM_I2S_CLOCKS 2
+
+struct artpec6_clkctrl_drvdata {
+	struct clk *clk_table[ARTPEC6_CLK_NUMCLOCKS];
+	void __iomem *syscon_base;
+	struct clk_onecell_data clk_data;
+	spinlock_t i2scfg_lock;
+};
+
+static struct artpec6_clkctrl_drvdata *clkdata;
+
+static const char *const i2s_clk_names[NUM_I2S_CLOCKS] = {
+	"i2s0",
+	"i2s1",
+};
+
+static const int i2s_clk_indexes[NUM_I2S_CLOCKS] = {
+	ARTPEC6_CLK_I2S0_CLK,
+	ARTPEC6_CLK_I2S1_CLK,
+};
+
+static void of_artpec6_clkctrl_setup(struct device_node *np)
+{
+	int i;
+	const char *sys_refclk_name;
+	u32 pll_mode, pll_m, pll_n;
+	struct clk **clks;
+
+	/* Mandatory parent clock. */
+	i = of_property_match_string(np, "clock-names", "sys_refclk");
+	if (i < 0)
+		return;
+
+	sys_refclk_name = of_clk_get_parent_name(np, i);
+
+	clkdata = kzalloc_obj(*clkdata);
+	if (!clkdata)
+		return;
+
+	clks = clkdata->clk_table;
+
+	for (i = 0; i < ARTPEC6_CLK_NUMCLOCKS; ++i)
+		clks[i] = ERR_PTR(-EPROBE_DEFER);
+
+	clkdata->syscon_base = of_iomap(np, 0);
+	BUG_ON(clkdata->syscon_base == NULL);
+
+	/* Read PLL1 factors configured by boot strap pins. */
+	pll_mode = (readl(clkdata->syscon_base) >> 6) & 3;
+	switch (pll_mode) {
+	case 0:		/* DDR3-2133 mode */
+		pll_m = 4;
+		pll_n = 85;
+		break;
+	case 1:		/* DDR3-1866 mode */
+		pll_m = 6;
+		pll_n = 112;
+		break;
+	case 2:		/* DDR3-1600 mode */
+		pll_m = 4;
+		pll_n = 64;
+		break;
+	case 3:		/* DDR3-1333 mode */
+		pll_m = 8;
+		pll_n = 106;
+		break;
+	}
+
+	clks[ARTPEC6_CLK_CPU] =
+	    clk_register_fixed_factor(NULL, "cpu", sys_refclk_name, 0, pll_n,
+				      pll_m);
+	clks[ARTPEC6_CLK_CPU_PERIPH] =
+	    clk_register_fixed_factor(NULL, "cpu_periph", "cpu", 0, 1, 2);
+
+	/* EPROBE_DEFER on the apb_clock is not handled in amba devices. */
+	clks[ARTPEC6_CLK_UART_PCLK] =
+	    clk_register_fixed_factor(NULL, "uart_pclk", "cpu", 0, 1, 8);
+	clks[ARTPEC6_CLK_UART_REFCLK] =
+	    clk_register_fixed_rate(NULL, "uart_ref", sys_refclk_name, 0,
+				    50000000);
+
+	clks[ARTPEC6_CLK_SPI_PCLK] =
+	    clk_register_fixed_factor(NULL, "spi_pclk", "cpu", 0, 1, 8);
+	clks[ARTPEC6_CLK_SPI_SSPCLK] =
+	    clk_register_fixed_rate(NULL, "spi_sspclk", sys_refclk_name, 0,
+				    50000000);
+
+	clks[ARTPEC6_CLK_DBG_PCLK] =
+	    clk_register_fixed_factor(NULL, "dbg_pclk", "cpu", 0, 1, 8);
+
+	clkdata->clk_data.clks = clkdata->clk_table;
+	clkdata->clk_data.clk_num = ARTPEC6_CLK_NUMCLOCKS;
+
+	of_clk_add_provider(np, of_clk_src_onecell_get, &clkdata->clk_data);
+}
+
+CLK_OF_DECLARE_DRIVER(artpec6_clkctrl, "axis,artpec6-clkctrl",
+		      of_artpec6_clkctrl_setup);
+
+static int artpec6_clkctrl_probe(struct platform_device *pdev)
+{
+	int propidx;
+	struct device_node *np = pdev->dev.of_node;
+	struct device *dev = &pdev->dev;
+	struct clk **clks = clkdata->clk_table;
+	const char *sys_refclk_name;
+	const char *i2s_refclk_name = NULL;
+	const char *frac_clk_name[2] = { NULL, NULL };
+	const char *i2s_mux_parents[2];
+	u32 muxreg;
+	int i;
+	int err = 0;
+
+	/* Mandatory parent clock. */
+	propidx = of_property_match_string(np, "clock-names", "sys_refclk");
+	if (propidx < 0)
+		return -EINVAL;
+
+	sys_refclk_name = of_clk_get_parent_name(np, propidx);
+
+	/* Find clock names of optional parent clocks. */
+	propidx = of_property_match_string(np, "clock-names", "i2s_refclk");
+	if (propidx >= 0)
+		i2s_refclk_name = of_clk_get_parent_name(np, propidx);
+
+	propidx = of_property_match_string(np, "clock-names", "frac_clk0");
+	if (propidx >= 0)
+		frac_clk_name[0] = of_clk_get_parent_name(np, propidx);
+	propidx = of_property_match_string(np, "clock-names", "frac_clk1");
+	if (propidx >= 0)
+		frac_clk_name[1] = of_clk_get_parent_name(np, propidx);
+
+	spin_lock_init(&clkdata->i2scfg_lock);
+
+	clks[ARTPEC6_CLK_NAND_CLKA] =
+	    clk_register_fixed_factor(dev, "nand_clka", "cpu", 0, 1, 8);
+	clks[ARTPEC6_CLK_NAND_CLKB] =
+	    clk_register_fixed_rate(dev, "nand_clkb", sys_refclk_name, 0,
+				    100000000);
+	clks[ARTPEC6_CLK_ETH_ACLK] =
+	    clk_register_fixed_factor(dev, "eth_aclk", "cpu", 0, 1, 4);
+	clks[ARTPEC6_CLK_DMA_ACLK] =
+	    clk_register_fixed_factor(dev, "dma_aclk", "cpu", 0, 1, 4);
+	clks[ARTPEC6_CLK_PTP_REF] =
+	    clk_register_fixed_rate(dev, "ptp_ref", sys_refclk_name, 0,
+				    100000000);
+	clks[ARTPEC6_CLK_SD_PCLK] =
+	    clk_register_fixed_rate(dev, "sd_pclk", sys_refclk_name, 0,
+				    100000000);
+	clks[ARTPEC6_CLK_SD_IMCLK] =
+	    clk_register_fixed_rate(dev, "sd_imclk", sys_refclk_name, 0,
+				    100000000);
+	clks[ARTPEC6_CLK_I2S_HST] =
+	    clk_register_fixed_factor(dev, "i2s_hst", "cpu", 0, 1, 8);
+
+	for (i = 0; i < NUM_I2S_CLOCKS; ++i) {
+		if (i2s_refclk_name && frac_clk_name[i]) {
+			i2s_mux_parents[0] = frac_clk_name[i];
+			i2s_mux_parents[1] = i2s_refclk_name;
+
+			clks[i2s_clk_indexes[i]] =
+			    clk_register_mux(dev, i2s_clk_names[i],
+					     i2s_mux_parents, 2,
+					     CLK_SET_RATE_NO_REPARENT |
+					     CLK_SET_RATE_PARENT,
+					     clkdata->syscon_base + 0x14, i, 1,
+					     0, &clkdata->i2scfg_lock);
+		} else if (frac_clk_name[i]) {
+			/* Lock the mux for internal clock reference. */
+			muxreg = readl(clkdata->syscon_base + 0x14);
+			muxreg &= ~BIT(i);
+			writel(muxreg, clkdata->syscon_base + 0x14);
+			clks[i2s_clk_indexes[i]] =
+			    clk_register_fixed_factor(dev, i2s_clk_names[i],
+						      frac_clk_name[i], 0, 1,
+						      1);
+		} else if (i2s_refclk_name) {
+			/* Lock the mux for external clock reference. */
+			muxreg = readl(clkdata->syscon_base + 0x14);
+			muxreg |= BIT(i);
+			writel(muxreg, clkdata->syscon_base + 0x14);
+			clks[i2s_clk_indexes[i]] =
+			    clk_register_fixed_factor(dev, i2s_clk_names[i],
+						      i2s_refclk_name, 0, 1, 1);
+		}
+	}
+
+	clks[ARTPEC6_CLK_I2C] =
+	    clk_register_fixed_rate(dev, "i2c", sys_refclk_name, 0, 100000000);
+
+	clks[ARTPEC6_CLK_SYS_TIMER] =
+	    clk_register_fixed_rate(dev, "timer", sys_refclk_name, 0,
+				    100000000);
+	clks[ARTPEC6_CLK_FRACDIV_IN] =
+	    clk_register_fixed_rate(dev, "fracdiv_in", sys_refclk_name, 0,
+				    600000000);
+
+	for (i = 0; i < ARTPEC6_CLK_NUMCLOCKS; ++i) {
+		if (IS_ERR(clks[i]) && PTR_ERR(clks[i]) != -EPROBE_DEFER) {
+			dev_err(dev,
+				"Failed to register clock at index %d err=%ld\n",
+				i, PTR_ERR(clks[i]));
+			err = PTR_ERR(clks[i]);
+		}
+	}
+
+	return err;
+}
+
+static const struct of_device_id artpec_clkctrl_of_match[] = {
+	{ .compatible = "axis,artpec6-clkctrl" },
+	{}
+};
+
+static struct platform_driver artpec6_clkctrl_driver = {
+	.probe = artpec6_clkctrl_probe,
+	.driver = {
+		   .name = "artpec6_clkctrl",
+		   .of_match_table = artpec_clkctrl_of_match,
+	},
+};
+
+builtin_platform_driver(artpec6_clkctrl_driver);