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, 210 insertions, 0 deletions

diff --git a/drivers/ssb/host_soc.c b/drivers/ssb/host_soc.c
new file mode 100644
index 000000000..3b4384805
--- /dev/null
+++ b/drivers/ssb/host_soc.c
@@ -0,0 +1,210 @@
+/*
+ * Sonics Silicon Backplane SoC host related functions.
+ * Subsystem core
+ *
+ * Copyright 2005, Broadcom Corporation
+ * Copyright 2006, 2007, Michael Buesch <m@bues.ch>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include "ssb_private.h"
+
+#include <linux/bcm47xx_nvram.h>
+#include <linux/ssb/ssb.h>
+
+static u8 ssb_host_soc_read8(struct ssb_device *dev, u16 offset)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	return readb(bus->mmio + offset);
+}
+
+static u16 ssb_host_soc_read16(struct ssb_device *dev, u16 offset)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	return readw(bus->mmio + offset);
+}
+
+static u32 ssb_host_soc_read32(struct ssb_device *dev, u16 offset)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	return readl(bus->mmio + offset);
+}
+
+#ifdef CONFIG_SSB_BLOCKIO
+static void ssb_host_soc_block_read(struct ssb_device *dev, void *buffer,
+				    size_t count, u16 offset, u8 reg_width)
+{
+	struct ssb_bus *bus = dev->bus;
+	void __iomem *addr;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	addr = bus->mmio + offset;
+
+	switch (reg_width) {
+	case sizeof(u8): {
+		u8 *buf = buffer;
+
+		while (count) {
+			*buf = __raw_readb(addr);
+			buf++;
+			count--;
+		}
+		break;
+	}
+	case sizeof(u16): {
+		__le16 *buf = buffer;
+
+		WARN_ON(count & 1);
+		while (count) {
+			*buf = (__force __le16)__raw_readw(addr);
+			buf++;
+			count -= 2;
+		}
+		break;
+	}
+	case sizeof(u32): {
+		__le32 *buf = buffer;
+
+		WARN_ON(count & 3);
+		while (count) {
+			*buf = (__force __le32)__raw_readl(addr);
+			buf++;
+			count -= 4;
+		}
+		break;
+	}
+	default:
+		WARN_ON(1);
+	}
+}
+#endif /* CONFIG_SSB_BLOCKIO */
+
+static void ssb_host_soc_write8(struct ssb_device *dev, u16 offset, u8 value)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	writeb(value, bus->mmio + offset);
+}
+
+static void ssb_host_soc_write16(struct ssb_device *dev, u16 offset, u16 value)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	writew(value, bus->mmio + offset);
+}
+
+static void ssb_host_soc_write32(struct ssb_device *dev, u16 offset, u32 value)
+{
+	struct ssb_bus *bus = dev->bus;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	writel(value, bus->mmio + offset);
+}
+
+#ifdef CONFIG_SSB_BLOCKIO
+static void ssb_host_soc_block_write(struct ssb_device *dev, const void *buffer,
+				     size_t count, u16 offset, u8 reg_width)
+{
+	struct ssb_bus *bus = dev->bus;
+	void __iomem *addr;
+
+	offset += dev->core_index * SSB_CORE_SIZE;
+	addr = bus->mmio + offset;
+
+	switch (reg_width) {
+	case sizeof(u8): {
+		const u8 *buf = buffer;
+
+		while (count) {
+			__raw_writeb(*buf, addr);
+			buf++;
+			count--;
+		}
+		break;
+	}
+	case sizeof(u16): {
+		const __le16 *buf = buffer;
+
+		WARN_ON(count & 1);
+		while (count) {
+			__raw_writew((__force u16)(*buf), addr);
+			buf++;
+			count -= 2;
+		}
+		break;
+	}
+	case sizeof(u32): {
+		const __le32 *buf = buffer;
+
+		WARN_ON(count & 3);
+		while (count) {
+			__raw_writel((__force u32)(*buf), addr);
+			buf++;
+			count -= 4;
+		}
+		break;
+	}
+	default:
+		WARN_ON(1);
+	}
+}
+#endif /* CONFIG_SSB_BLOCKIO */
+
+/* Ops for the plain SSB bus without a host-device (no PCI or PCMCIA). */
+const struct ssb_bus_ops ssb_host_soc_ops = {
+	.read8		= ssb_host_soc_read8,
+	.read16		= ssb_host_soc_read16,
+	.read32		= ssb_host_soc_read32,
+	.write8		= ssb_host_soc_write8,
+	.write16	= ssb_host_soc_write16,
+	.write32	= ssb_host_soc_write32,
+#ifdef CONFIG_SSB_BLOCKIO
+	.block_read	= ssb_host_soc_block_read,
+	.block_write	= ssb_host_soc_block_write,
+#endif
+};
+
+int ssb_host_soc_get_invariants(struct ssb_bus *bus,
+				struct ssb_init_invariants *iv)
+{
+	char buf[20];
+	int len, err;
+
+	/* Fill boardinfo structure */
+	memset(&iv->boardinfo, 0, sizeof(struct ssb_boardinfo));
+
+	len = bcm47xx_nvram_getenv("boardvendor", buf, sizeof(buf));
+	if (len > 0) {
+		err = kstrtou16(strim(buf), 0, &iv->boardinfo.vendor);
+		if (err)
+			pr_warn("Couldn't parse nvram board vendor entry with value \"%s\"\n",
+				buf);
+	}
+	if (!iv->boardinfo.vendor)
+		iv->boardinfo.vendor = SSB_BOARDVENDOR_BCM;
+
+	len = bcm47xx_nvram_getenv("boardtype", buf, sizeof(buf));
+	if (len > 0) {
+		err = kstrtou16(strim(buf), 0, &iv->boardinfo.type);
+		if (err)
+			pr_warn("Couldn't parse nvram board type entry with value \"%s\"\n",
+				buf);
+	}
+
+	memset(&iv->sprom, 0, sizeof(struct ssb_sprom));
+	ssb_fill_sprom_with_fallback(bus, &iv->sprom);
+
+	if (bcm47xx_nvram_getenv("cardbus", buf, sizeof(buf)) >= 0)
+		iv->has_cardbus_slot = !!simple_strtoul(buf, NULL, 10);
+
+	return 0;
+}