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, 377 insertions, 0 deletions

diff --git a/arch/powerpc/boot/devtree.c b/arch/powerpc/boot/devtree.c
new file mode 100644
index 000000000..58fbcfcc9
--- /dev/null
+++ b/arch/powerpc/boot/devtree.c
@@ -0,0 +1,377 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * devtree.c - convenience functions for device tree manipulation
+ * Copyright 2007 David Gibson, IBM Corporation.
+ * Copyright (c) 2007 Freescale Semiconductor, Inc.
+ *
+ * Authors: David Gibson <david@gibson.dropbear.id.au>
+ *	    Scott Wood <scottwood@freescale.com>
+ */
+#include <stdarg.h>
+#include <stddef.h>
+#include "types.h"
+#include "string.h"
+#include "stdio.h"
+#include "ops.h"
+#include "of.h"
+
+void dt_fixup_memory(u64 start, u64 size)
+{
+	void *root, *memory;
+	int naddr, nsize, i;
+	u32 memreg[4];
+
+	root = finddevice("/");
+	if (getprop(root, "#address-cells", &naddr, sizeof(naddr)) < 0)
+		naddr = 2;
+	else
+		naddr = be32_to_cpu(naddr);
+	if (naddr < 1 || naddr > 2)
+		fatal("Can't cope with #address-cells == %d in /\n\r", naddr);
+
+	if (getprop(root, "#size-cells", &nsize, sizeof(nsize)) < 0)
+		nsize = 1;
+	else
+		nsize = be32_to_cpu(nsize);
+	if (nsize < 1 || nsize > 2)
+		fatal("Can't cope with #size-cells == %d in /\n\r", nsize);
+
+	i = 0;
+	if (naddr == 2)
+		memreg[i++] = cpu_to_be32(start >> 32);
+	memreg[i++] = cpu_to_be32(start & 0xffffffff);
+	if (nsize == 2)
+		memreg[i++] = cpu_to_be32(size >> 32);
+	memreg[i++] = cpu_to_be32(size & 0xffffffff);
+
+	memory = finddevice("/memory");
+	if (! memory) {
+		memory = create_node(NULL, "memory");
+		setprop_str(memory, "device_type", "memory");
+	}
+
+	printf("Memory <- <0x%x", be32_to_cpu(memreg[0]));
+	for (i = 1; i < (naddr + nsize); i++)
+		printf(" 0x%x", be32_to_cpu(memreg[i]));
+	printf("> (%ldMB)\n\r", (unsigned long)(size >> 20));
+
+	setprop(memory, "reg", memreg, (naddr + nsize)*sizeof(u32));
+}
+
+#define MHZ(x)	((x + 500000) / 1000000)
+
+void dt_fixup_cpu_clocks(u32 cpu, u32 tb, u32 bus)
+{
+	void *devp = NULL;
+
+	printf("CPU clock-frequency <- 0x%x (%dMHz)\n\r", cpu, MHZ(cpu));
+	printf("CPU timebase-frequency <- 0x%x (%dMHz)\n\r", tb, MHZ(tb));
+	if (bus > 0)
+		printf("CPU bus-frequency <- 0x%x (%dMHz)\n\r", bus, MHZ(bus));
+
+	while ((devp = find_node_by_devtype(devp, "cpu"))) {
+		setprop_val(devp, "clock-frequency", cpu_to_be32(cpu));
+		setprop_val(devp, "timebase-frequency", cpu_to_be32(tb));
+		if (bus > 0)
+			setprop_val(devp, "bus-frequency", cpu_to_be32(bus));
+	}
+
+	timebase_period_ns = 1000000000 / tb;
+}
+
+void dt_fixup_clock(const char *path, u32 freq)
+{
+	void *devp = finddevice(path);
+
+	if (devp) {
+		printf("%s: clock-frequency <- %x (%dMHz)\n\r", path, freq, MHZ(freq));
+		setprop_val(devp, "clock-frequency", cpu_to_be32(freq));
+	}
+}
+
+void dt_fixup_mac_address_by_alias(const char *alias, const u8 *addr)
+{
+	void *devp = find_node_by_alias(alias);
+
+	if (devp) {
+		printf("%s: local-mac-address <-"
+		       " %02x:%02x:%02x:%02x:%02x:%02x\n\r", alias,
+		       addr[0], addr[1], addr[2],
+		       addr[3], addr[4], addr[5]);
+
+		setprop(devp, "local-mac-address", addr, 6);
+	}
+}
+
+void dt_fixup_mac_address(u32 index, const u8 *addr)
+{
+	void *devp = find_node_by_prop_value(NULL, "linux,network-index",
+	                                     (void*)&index, sizeof(index));
+
+	if (devp) {
+		printf("ENET%d: local-mac-address <-"
+		       " %02x:%02x:%02x:%02x:%02x:%02x\n\r", index,
+		       addr[0], addr[1], addr[2],
+		       addr[3], addr[4], addr[5]);
+
+		setprop(devp, "local-mac-address", addr, 6);
+	}
+}
+
+void __dt_fixup_mac_addresses(u32 startindex, ...)
+{
+	va_list ap;
+	u32 index = startindex;
+	const u8 *addr;
+
+	va_start(ap, startindex);
+
+	while ((addr = va_arg(ap, const u8 *)))
+		dt_fixup_mac_address(index++, addr);
+
+	va_end(ap);
+}
+
+#define MAX_ADDR_CELLS 4
+
+void dt_get_reg_format(void *node, u32 *naddr, u32 *nsize)
+{
+	if (getprop(node, "#address-cells", naddr, 4) != 4)
+		*naddr = 2;
+	else
+		*naddr = be32_to_cpu(*naddr);
+	if (getprop(node, "#size-cells", nsize, 4) != 4)
+		*nsize = 1;
+	else
+		*nsize = be32_to_cpu(*nsize);
+}
+
+static void copy_val(u32 *dest, u32 *src, int naddr)
+{
+	int pad = MAX_ADDR_CELLS - naddr;
+
+	memset(dest, 0, pad * 4);
+	memcpy(dest + pad, src, naddr * 4);
+}
+
+static int sub_reg(u32 *reg, u32 *sub)
+{
+	int i, borrow = 0;
+
+	for (i = MAX_ADDR_CELLS - 1; i >= 0; i--) {
+		int prev_borrow = borrow;
+		borrow = reg[i] < sub[i] + prev_borrow;
+		reg[i] -= sub[i] + prev_borrow;
+	}
+
+	return !borrow;
+}
+
+static int add_reg(u32 *reg, u32 *add, int naddr)
+{
+	int i, carry = 0;
+
+	for (i = MAX_ADDR_CELLS - 1; i >= MAX_ADDR_CELLS - naddr; i--) {
+		u64 tmp = (u64)be32_to_cpu(reg[i]) + be32_to_cpu(add[i]) + carry;
+		carry = tmp >> 32;
+		reg[i] = cpu_to_be32((u32)tmp);
+	}
+
+	return !carry;
+}
+
+/* It is assumed that if the first byte of reg fits in a
+ * range, then the whole reg block fits.
+ */
+static int compare_reg(u32 *reg, u32 *range, u32 *rangesize)
+{
+	int i;
+	u32 end;
+
+	for (i = 0; i < MAX_ADDR_CELLS; i++) {
+		if (be32_to_cpu(reg[i]) < be32_to_cpu(range[i]))
+			return 0;
+		if (be32_to_cpu(reg[i]) > be32_to_cpu(range[i]))
+			break;
+	}
+
+	for (i = 0; i < MAX_ADDR_CELLS; i++) {
+		end = be32_to_cpu(range[i]) + be32_to_cpu(rangesize[i]);
+
+		if (be32_to_cpu(reg[i]) < end)
+			break;
+		if (be32_to_cpu(reg[i]) > end)
+			return 0;
+	}
+
+	return reg[i] != end;
+}
+
+/* reg must be MAX_ADDR_CELLS */
+static int find_range(u32 *reg, u32 *ranges, int nregaddr,
+                      int naddr, int nsize, int buflen)
+{
+	int nrange = nregaddr + naddr + nsize;
+	int i;
+
+	for (i = 0; i + nrange <= buflen; i += nrange) {
+		u32 range_addr[MAX_ADDR_CELLS];
+		u32 range_size[MAX_ADDR_CELLS];
+
+		copy_val(range_addr, ranges + i, nregaddr);
+		copy_val(range_size, ranges + i + nregaddr + naddr, nsize);
+
+		if (compare_reg(reg, range_addr, range_size))
+			return i;
+	}
+
+	return -1;
+}
+
+/* Currently only generic buses without special encodings are supported.
+ * In particular, PCI is not supported.  Also, only the beginning of the
+ * reg block is tracked; size is ignored except in ranges.
+ */
+static u32 prop_buf[MAX_PROP_LEN / 4];
+
+static int dt_xlate(void *node, int res, int reglen, unsigned long *addr,
+		unsigned long *size)
+{
+	u32 last_addr[MAX_ADDR_CELLS];
+	u32 this_addr[MAX_ADDR_CELLS];
+	void *parent;
+	u64 ret_addr, ret_size;
+	u32 naddr, nsize, prev_naddr, prev_nsize;
+	int buflen, offset;
+
+	parent = get_parent(node);
+	if (!parent)
+		return 0;
+
+	dt_get_reg_format(parent, &naddr, &nsize);
+	if (nsize > 2)
+		return 0;
+
+	offset = (naddr + nsize) * res;
+
+	if (reglen < offset + naddr + nsize ||
+	    MAX_PROP_LEN < (offset + naddr + nsize) * 4)
+		return 0;
+
+	copy_val(last_addr, prop_buf + offset, naddr);
+
+	ret_size = be32_to_cpu(prop_buf[offset + naddr]);
+	if (nsize == 2) {
+		ret_size <<= 32;
+		ret_size |= be32_to_cpu(prop_buf[offset + naddr + 1]);
+	}
+
+	for (;;) {
+		prev_naddr = naddr;
+		prev_nsize = nsize;
+		node = parent;
+
+		parent = get_parent(node);
+		if (!parent)
+			break;
+
+		dt_get_reg_format(parent, &naddr, &nsize);
+
+		buflen = getprop(node, "ranges", prop_buf,
+				sizeof(prop_buf));
+		if (buflen == 0)
+			continue;
+		if (buflen < 0 || buflen > sizeof(prop_buf))
+			return 0;
+
+		offset = find_range(last_addr, prop_buf, prev_naddr,
+		                    naddr, prev_nsize, buflen / 4);
+		if (offset < 0)
+			return 0;
+
+		copy_val(this_addr, prop_buf + offset, prev_naddr);
+
+		if (!sub_reg(last_addr, this_addr))
+			return 0;
+
+		copy_val(this_addr, prop_buf + offset + prev_naddr, naddr);
+
+		if (!add_reg(last_addr, this_addr, naddr))
+			return 0;
+	}
+
+	if (naddr > 2)
+		return 0;
+
+	ret_addr = ((u64)be32_to_cpu(last_addr[2]) << 32) | be32_to_cpu(last_addr[3]);
+	if (sizeof(void *) == 4 &&
+	    (ret_addr >= 0x100000000ULL || ret_size > 0x100000000ULL ||
+	     ret_addr + ret_size > 0x100000000ULL))
+		return 0;
+
+	*addr = ret_addr;
+	if (size)
+		*size = ret_size;
+
+	return 1;
+}
+
+int dt_xlate_reg(void *node, int res, unsigned long *addr, unsigned long *size)
+{
+	int reglen;
+
+	reglen = getprop(node, "reg", prop_buf, sizeof(prop_buf)) / 4;
+	return dt_xlate(node, res, reglen, addr, size);
+}
+
+int dt_xlate_addr(void *node, u32 *buf, int buflen, unsigned long *xlated_addr)
+{
+
+	if (buflen > sizeof(prop_buf))
+		return 0;
+
+	memcpy(prop_buf, buf, buflen);
+	return dt_xlate(node, 0, buflen / 4, xlated_addr, NULL);
+}
+
+int dt_is_compatible(void *node, const char *compat)
+{
+	char *buf = (char *)prop_buf;
+	int len, pos;
+
+	len = getprop(node, "compatible", buf, MAX_PROP_LEN);
+	if (len < 0)
+		return 0;
+
+	for (pos = 0; pos < len; pos++) {
+		if (!strcmp(buf + pos, compat))
+			return 1;
+
+		pos += strnlen(&buf[pos], len - pos);
+	}
+
+	return 0;
+}
+
+int dt_get_virtual_reg(void *node, void **addr, int nres)
+{
+	unsigned long xaddr;
+	int n, i;
+
+	n = getprop(node, "virtual-reg", addr, nres * 4);
+	if (n > 0) {
+		for (i = 0; i < n/4; i ++)
+			((u32 *)addr)[i] = be32_to_cpu(((u32 *)addr)[i]);
+		return n / 4;
+	}
+
+	for (n = 0; n < nres; n++) {
+		if (!dt_xlate_reg(node, n, &xaddr, NULL))
+			break;
+
+		addr[n] = (void *)xaddr;
+	}
+
+	return n;
+}
+