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, 344 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/cpm2.c b/arch/powerpc/sysdev/cpm2.c
new file mode 100644
index 000000000..14cc5ea93
--- /dev/null
+++ b/arch/powerpc/sysdev/cpm2.c
@@ -0,0 +1,344 @@
+/*
+ * General Purpose functions for the global management of the
+ * 8260 Communication Processor Module.
+ * Copyright (c) 1999-2001 Dan Malek <dan@embeddedalley.com>
+ * Copyright (c) 2000 MontaVista Software, Inc (source@mvista.com)
+ *	2.3.99 Updates
+ *
+ * 2006 (c) MontaVista Software, Inc.
+ * Vitaly Bordug <vbordug@ru.mvista.com>
+ * 	Merged to arch/powerpc from arch/ppc/syslib/cpm2_common.c
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2. This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ */
+
+/*
+ *
+ * In addition to the individual control of the communication
+ * channels, there are a few functions that globally affect the
+ * communication processor.
+ *
+ * Buffer descriptors must be allocated from the dual ported memory
+ * space.  The allocator for that is here.  When the communication
+ * process is reset, we reclaim the memory available.  There is
+ * currently no deallocator for this memory.
+ */
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/param.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+#include <asm/io.h>
+#include <asm/irq.h>
+#include <asm/page.h>
+#include <asm/cpm2.h>
+#include <asm/rheap.h>
+
+#include <sysdev/fsl_soc.h>
+
+cpm_cpm2_t __iomem *cpmp; /* Pointer to comm processor space */
+
+/* We allocate this here because it is used almost exclusively for
+ * the communication processor devices.
+ */
+cpm2_map_t __iomem *cpm2_immr;
+EXPORT_SYMBOL(cpm2_immr);
+
+#define CPM_MAP_SIZE	(0x40000)	/* 256k - the PQ3 reserve this amount
+					   of space for CPM as it is larger
+					   than on PQ2 */
+
+void __init cpm2_reset(void)
+{
+#ifdef CONFIG_PPC_85xx
+	cpm2_immr = ioremap(get_immrbase() + 0x80000, CPM_MAP_SIZE);
+#else
+	cpm2_immr = ioremap(get_immrbase(), CPM_MAP_SIZE);
+#endif
+
+	/* Tell everyone where the comm processor resides.
+	 */
+	cpmp = &cpm2_immr->im_cpm;
+
+#ifndef CONFIG_PPC_EARLY_DEBUG_CPM
+	/* Reset the CPM.
+	 */
+	cpm_command(CPM_CR_RST, 0);
+#endif
+}
+
+static DEFINE_SPINLOCK(cmd_lock);
+
+#define MAX_CR_CMD_LOOPS        10000
+
+int cpm_command(u32 command, u8 opcode)
+{
+	int i, ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cmd_lock, flags);
+
+	ret = 0;
+	out_be32(&cpmp->cp_cpcr, command | opcode | CPM_CR_FLG);
+	for (i = 0; i < MAX_CR_CMD_LOOPS; i++)
+		if ((in_be32(&cpmp->cp_cpcr) & CPM_CR_FLG) == 0)
+			goto out;
+
+	printk(KERN_ERR "%s(): Not able to issue CPM command\n", __func__);
+	ret = -EIO;
+out:
+	spin_unlock_irqrestore(&cmd_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(cpm_command);
+
+/* Set a baud rate generator.  This needs lots of work.  There are
+ * eight BRGs, which can be connected to the CPM channels or output
+ * as clocks.  The BRGs are in two different block of internal
+ * memory mapped space.
+ * The baud rate clock is the system clock divided by something.
+ * It was set up long ago during the initial boot phase and is
+ * given to us.
+ * Baud rate clocks are zero-based in the driver code (as that maps
+ * to port numbers).  Documentation uses 1-based numbering.
+ */
+void __cpm2_setbrg(uint brg, uint rate, uint clk, int div16, int src)
+{
+	u32 __iomem *bp;
+	u32 val;
+
+	/* This is good enough to get SMCs running.....
+	*/
+	if (brg < 4) {
+		bp = &cpm2_immr->im_brgc1;
+	} else {
+		bp = &cpm2_immr->im_brgc5;
+		brg -= 4;
+	}
+	bp += brg;
+	/* Round the clock divider to the nearest integer. */
+	val = (((clk * 2 / rate) - 1) & ~1) | CPM_BRG_EN | src;
+	if (div16)
+		val |= CPM_BRG_DIV16;
+
+	out_be32(bp, val);
+}
+EXPORT_SYMBOL(__cpm2_setbrg);
+
+int __init cpm2_clk_setup(enum cpm_clk_target target, int clock, int mode)
+{
+	int ret = 0;
+	int shift;
+	int i, bits = 0;
+	u32 __iomem *reg;
+	u32 mask = 7;
+
+	u8 clk_map[][3] = {
+		{CPM_CLK_FCC1, CPM_BRG5, 0},
+		{CPM_CLK_FCC1, CPM_BRG6, 1},
+		{CPM_CLK_FCC1, CPM_BRG7, 2},
+		{CPM_CLK_FCC1, CPM_BRG8, 3},
+		{CPM_CLK_FCC1, CPM_CLK9, 4},
+		{CPM_CLK_FCC1, CPM_CLK10, 5},
+		{CPM_CLK_FCC1, CPM_CLK11, 6},
+		{CPM_CLK_FCC1, CPM_CLK12, 7},
+		{CPM_CLK_FCC2, CPM_BRG5, 0},
+		{CPM_CLK_FCC2, CPM_BRG6, 1},
+		{CPM_CLK_FCC2, CPM_BRG7, 2},
+		{CPM_CLK_FCC2, CPM_BRG8, 3},
+		{CPM_CLK_FCC2, CPM_CLK13, 4},
+		{CPM_CLK_FCC2, CPM_CLK14, 5},
+		{CPM_CLK_FCC2, CPM_CLK15, 6},
+		{CPM_CLK_FCC2, CPM_CLK16, 7},
+		{CPM_CLK_FCC3, CPM_BRG5, 0},
+		{CPM_CLK_FCC3, CPM_BRG6, 1},
+		{CPM_CLK_FCC3, CPM_BRG7, 2},
+		{CPM_CLK_FCC3, CPM_BRG8, 3},
+		{CPM_CLK_FCC3, CPM_CLK13, 4},
+		{CPM_CLK_FCC3, CPM_CLK14, 5},
+		{CPM_CLK_FCC3, CPM_CLK15, 6},
+		{CPM_CLK_FCC3, CPM_CLK16, 7},
+		{CPM_CLK_SCC1, CPM_BRG1, 0},
+		{CPM_CLK_SCC1, CPM_BRG2, 1},
+		{CPM_CLK_SCC1, CPM_BRG3, 2},
+		{CPM_CLK_SCC1, CPM_BRG4, 3},
+		{CPM_CLK_SCC1, CPM_CLK11, 4},
+		{CPM_CLK_SCC1, CPM_CLK12, 5},
+		{CPM_CLK_SCC1, CPM_CLK3, 6},
+		{CPM_CLK_SCC1, CPM_CLK4, 7},
+		{CPM_CLK_SCC2, CPM_BRG1, 0},
+		{CPM_CLK_SCC2, CPM_BRG2, 1},
+		{CPM_CLK_SCC2, CPM_BRG3, 2},
+		{CPM_CLK_SCC2, CPM_BRG4, 3},
+		{CPM_CLK_SCC2, CPM_CLK11, 4},
+		{CPM_CLK_SCC2, CPM_CLK12, 5},
+		{CPM_CLK_SCC2, CPM_CLK3, 6},
+		{CPM_CLK_SCC2, CPM_CLK4, 7},
+		{CPM_CLK_SCC3, CPM_BRG1, 0},
+		{CPM_CLK_SCC3, CPM_BRG2, 1},
+		{CPM_CLK_SCC3, CPM_BRG3, 2},
+		{CPM_CLK_SCC3, CPM_BRG4, 3},
+		{CPM_CLK_SCC3, CPM_CLK5, 4},
+		{CPM_CLK_SCC3, CPM_CLK6, 5},
+		{CPM_CLK_SCC3, CPM_CLK7, 6},
+		{CPM_CLK_SCC3, CPM_CLK8, 7},
+		{CPM_CLK_SCC4, CPM_BRG1, 0},
+		{CPM_CLK_SCC4, CPM_BRG2, 1},
+		{CPM_CLK_SCC4, CPM_BRG3, 2},
+		{CPM_CLK_SCC4, CPM_BRG4, 3},
+		{CPM_CLK_SCC4, CPM_CLK5, 4},
+		{CPM_CLK_SCC4, CPM_CLK6, 5},
+		{CPM_CLK_SCC4, CPM_CLK7, 6},
+		{CPM_CLK_SCC4, CPM_CLK8, 7},
+	};
+
+	switch (target) {
+	case CPM_CLK_SCC1:
+		reg = &cpm2_immr->im_cpmux.cmx_scr;
+		shift = 24;
+		break;
+	case CPM_CLK_SCC2:
+		reg = &cpm2_immr->im_cpmux.cmx_scr;
+		shift = 16;
+		break;
+	case CPM_CLK_SCC3:
+		reg = &cpm2_immr->im_cpmux.cmx_scr;
+		shift = 8;
+		break;
+	case CPM_CLK_SCC4:
+		reg = &cpm2_immr->im_cpmux.cmx_scr;
+		shift = 0;
+		break;
+	case CPM_CLK_FCC1:
+		reg = &cpm2_immr->im_cpmux.cmx_fcr;
+		shift = 24;
+		break;
+	case CPM_CLK_FCC2:
+		reg = &cpm2_immr->im_cpmux.cmx_fcr;
+		shift = 16;
+		break;
+	case CPM_CLK_FCC3:
+		reg = &cpm2_immr->im_cpmux.cmx_fcr;
+		shift = 8;
+		break;
+	default:
+		printk(KERN_ERR "cpm2_clock_setup: invalid clock target\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(clk_map); i++) {
+		if (clk_map[i][0] == target && clk_map[i][1] == clock) {
+			bits = clk_map[i][2];
+			break;
+		}
+	}
+	if (i == ARRAY_SIZE(clk_map))
+	    ret = -EINVAL;
+
+	bits <<= shift;
+	mask <<= shift;
+
+	if (mode == CPM_CLK_RTX) {
+		bits |= bits << 3;
+		mask |= mask << 3;
+	} else if (mode == CPM_CLK_RX) {
+		bits <<= 3;
+		mask <<= 3;
+	}
+
+	out_be32(reg, (in_be32(reg) & ~mask) | bits);
+
+	return ret;
+}
+
+int __init cpm2_smc_clk_setup(enum cpm_clk_target target, int clock)
+{
+	int ret = 0;
+	int shift;
+	int i, bits = 0;
+	u8 __iomem *reg;
+	u8 mask = 3;
+
+	u8 clk_map[][3] = {
+		{CPM_CLK_SMC1, CPM_BRG1, 0},
+		{CPM_CLK_SMC1, CPM_BRG7, 1},
+		{CPM_CLK_SMC1, CPM_CLK7, 2},
+		{CPM_CLK_SMC1, CPM_CLK9, 3},
+		{CPM_CLK_SMC2, CPM_BRG2, 0},
+		{CPM_CLK_SMC2, CPM_BRG8, 1},
+		{CPM_CLK_SMC2, CPM_CLK4, 2},
+		{CPM_CLK_SMC2, CPM_CLK15, 3},
+	};
+
+	switch (target) {
+	case CPM_CLK_SMC1:
+		reg = &cpm2_immr->im_cpmux.cmx_smr;
+		mask = 3;
+		shift = 4;
+		break;
+	case CPM_CLK_SMC2:
+		reg = &cpm2_immr->im_cpmux.cmx_smr;
+		mask = 3;
+		shift = 0;
+		break;
+	default:
+		printk(KERN_ERR "cpm2_smc_clock_setup: invalid clock target\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(clk_map); i++) {
+		if (clk_map[i][0] == target && clk_map[i][1] == clock) {
+			bits = clk_map[i][2];
+			break;
+		}
+	}
+	if (i == ARRAY_SIZE(clk_map))
+	    ret = -EINVAL;
+
+	bits <<= shift;
+	mask <<= shift;
+
+	out_8(reg, (in_8(reg) & ~mask) | bits);
+
+	return ret;
+}
+
+struct cpm2_ioports {
+	u32 dir, par, sor, odr, dat;
+	u32 res[3];
+};
+
+void __init cpm2_set_pin(int port, int pin, int flags)
+{
+	struct cpm2_ioports __iomem *iop =
+		(struct cpm2_ioports __iomem *)&cpm2_immr->im_ioport;
+
+	pin = 1 << (31 - pin);
+
+	if (flags & CPM_PIN_OUTPUT)
+		setbits32(&iop[port].dir, pin);
+	else
+		clrbits32(&iop[port].dir, pin);
+
+	if (!(flags & CPM_PIN_GPIO))
+		setbits32(&iop[port].par, pin);
+	else
+		clrbits32(&iop[port].par, pin);
+
+	if (flags & CPM_PIN_SECONDARY)
+		setbits32(&iop[port].sor, pin);
+	else
+		clrbits32(&iop[port].sor, pin);
+
+	if (flags & CPM_PIN_OPENDRAIN)
+		setbits32(&iop[port].odr, pin);
+	else
+		clrbits32(&iop[port].odr, pin);
+}