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, 259 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
new file mode 100644
index 000000000..a40c2162a
--- /dev/null
+++ b/arch/powerpc/boot/ops.h
@@ -0,0 +1,259 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Global definition of all the bootwrapper operations.
+ *
+ * Author: Mark A. Greer <mgreer@mvista.com>
+ *
+ * 2006 (c) MontaVista Software, Inc.
+ */
+#ifndef _PPC_BOOT_OPS_H_
+#define _PPC_BOOT_OPS_H_
+
+#include <stddef.h>
+#include "types.h"
+#include "string.h"
+
+#define	BOOT_COMMAND_LINE_SIZE	2048
+#define	MAX_PATH_LEN		256
+#define	MAX_PROP_LEN		256 /* What should this be? */
+
+typedef void (*kernel_entry_t)(unsigned long r3, unsigned long r4, void *r5);
+
+/* Platform specific operations */
+struct platform_ops {
+	void	(*fixups)(void);
+	void	(*image_hdr)(const void *);
+	void *	(*malloc)(unsigned long size);
+	void	(*free)(void *ptr);
+	void *	(*realloc)(void *ptr, unsigned long size);
+	void	(*exit)(void);
+	void *	(*vmlinux_alloc)(unsigned long size);
+	void  	(*kentry)(unsigned long fdt_addr, void *vmlinux_addr);
+};
+extern struct platform_ops platform_ops;
+
+/* Device Tree operations */
+struct dt_ops {
+	void *	(*finddevice)(const char *name);
+	int	(*getprop)(const void *phandle, const char *name, void *buf,
+			const int buflen);
+	int	(*setprop)(const void *phandle, const char *name,
+			const void *buf, const int buflen);
+	int (*del_node)(const void *phandle);
+	void *(*get_parent)(const void *phandle);
+	/* The node must not already exist. */
+	void *(*create_node)(const void *parent, const char *name);
+	void *(*find_node_by_prop_value)(const void *prev,
+	                                 const char *propname,
+	                                 const char *propval, int proplen);
+	void *(*find_node_by_compatible)(const void *prev,
+	                                 const char *compat);
+	unsigned long (*finalize)(void);
+	char *(*get_path)(const void *phandle, char *buf, int len);
+};
+extern struct dt_ops dt_ops;
+
+/* Console operations */
+struct console_ops {
+	int	(*open)(void);
+	void	(*write)(const char *buf, int len);
+	void	(*edit_cmdline)(char *buf, int len, unsigned int getline_timeout);
+	void	(*close)(void);
+	void	*data;
+};
+extern struct console_ops console_ops;
+
+/* Serial console operations */
+struct serial_console_data {
+	int		(*open)(void);
+	void		(*putc)(unsigned char c);
+	unsigned char	(*getc)(void);
+	u8		(*tstc)(void);
+	void		(*close)(void);
+};
+
+struct loader_info {
+	void *promptr;
+	unsigned long initrd_addr, initrd_size;
+	char *cmdline;
+	int cmdline_len;
+};
+extern struct loader_info loader_info;
+
+void start(void);
+void fdt_init(void *blob);
+int serial_console_init(void);
+int ns16550_console_init(void *devp, struct serial_console_data *scdp);
+int cpm_console_init(void *devp, struct serial_console_data *scdp);
+int mpc5200_psc_console_init(void *devp, struct serial_console_data *scdp);
+int opal_console_init(void *devp, struct serial_console_data *scdp);
+void *simple_alloc_init(char *base, unsigned long heap_size,
+			unsigned long granularity, unsigned long max_allocs);
+extern void flush_cache(void *, unsigned long);
+int dt_xlate_reg(void *node, int res, unsigned long *addr, unsigned long *size);
+int dt_xlate_addr(void *node, u32 *buf, int buflen, unsigned long *xlated_addr);
+int dt_is_compatible(void *node, const char *compat);
+void dt_get_reg_format(void *node, u32 *naddr, u32 *nsize);
+int dt_get_virtual_reg(void *node, void **addr, int nres);
+
+static inline void *finddevice(const char *name)
+{
+	return (dt_ops.finddevice) ? dt_ops.finddevice(name) : NULL;
+}
+
+static inline int getprop(void *devp, const char *name, void *buf, int buflen)
+{
+	return (dt_ops.getprop) ? dt_ops.getprop(devp, name, buf, buflen) : -1;
+}
+
+static inline int setprop(void *devp, const char *name,
+                          const void *buf, int buflen)
+{
+	return (dt_ops.setprop) ? dt_ops.setprop(devp, name, buf, buflen) : -1;
+}
+#define setprop_val(devp, name, val) \
+	do { \
+		typeof(val) x = (val); \
+		setprop((devp), (name), &x, sizeof(x)); \
+	} while (0)
+
+static inline int setprop_str(void *devp, const char *name, const char *buf)
+{
+	if (dt_ops.setprop)
+		return dt_ops.setprop(devp, name, buf, strlen(buf) + 1);
+
+	return -1;
+}
+
+static inline int del_node(const void *devp)
+{
+	return dt_ops.del_node ? dt_ops.del_node(devp) : -1;
+}
+
+static inline void *get_parent(const char *devp)
+{
+	return dt_ops.get_parent ? dt_ops.get_parent(devp) : NULL;
+}
+
+static inline void *create_node(const void *parent, const char *name)
+{
+	return dt_ops.create_node ? dt_ops.create_node(parent, name) : NULL;
+}
+
+
+static inline void *find_node_by_prop_value(const void *prev,
+                                            const char *propname,
+                                            const char *propval, int proplen)
+{
+	if (dt_ops.find_node_by_prop_value)
+		return dt_ops.find_node_by_prop_value(prev, propname,
+		                                      propval, proplen);
+
+	return NULL;
+}
+
+static inline void *find_node_by_prop_value_str(const void *prev,
+                                                const char *propname,
+                                                const char *propval)
+{
+	return find_node_by_prop_value(prev, propname, propval,
+	                               strlen(propval) + 1);
+}
+
+static inline void *find_node_by_devtype(const void *prev,
+                                         const char *type)
+{
+	return find_node_by_prop_value_str(prev, "device_type", type);
+}
+
+static inline void *find_node_by_alias(const char *alias)
+{
+	void *devp = finddevice("/aliases");
+
+	if (devp) {
+		char path[MAX_PATH_LEN];
+		if (getprop(devp, alias, path, MAX_PATH_LEN) > 0)
+			return finddevice(path);
+	}
+
+	return NULL;
+}
+
+static inline void *find_node_by_compatible(const void *prev,
+                                            const char *compat)
+{
+	if (dt_ops.find_node_by_compatible)
+		return dt_ops.find_node_by_compatible(prev, compat);
+
+	return NULL;
+}
+
+void dt_fixup_memory(u64 start, u64 size);
+void dt_fixup_cpu_clocks(u32 cpufreq, u32 tbfreq, u32 busfreq);
+void dt_fixup_clock(const char *path, u32 freq);
+void dt_fixup_mac_address_by_alias(const char *alias, const u8 *addr);
+void dt_fixup_mac_address(u32 index, const u8 *addr);
+void __dt_fixup_mac_addresses(u32 startindex, ...);
+#define dt_fixup_mac_addresses(...) \
+	__dt_fixup_mac_addresses(0, __VA_ARGS__, NULL)
+
+
+static inline char *get_path(const void *phandle, char *buf, int len)
+{
+	if (dt_ops.get_path)
+		return dt_ops.get_path(phandle, buf, len);
+
+	return NULL;
+}
+
+static inline void *malloc(unsigned long size)
+{
+	return (platform_ops.malloc) ? platform_ops.malloc(size) : NULL;
+}
+
+static inline void free(void *ptr)
+{
+	if (platform_ops.free)
+		platform_ops.free(ptr);
+}
+
+static inline void exit(void)
+{
+	if (platform_ops.exit)
+		platform_ops.exit();
+	for(;;);
+}
+#define fatal(args...) { printf(args); exit(); }
+
+
+#define BSS_STACK(size) \
+	static char _bss_stack[size]; \
+	void *_platform_stack_top = _bss_stack + sizeof(_bss_stack);
+
+extern unsigned long timebase_period_ns;
+void udelay(long delay);
+
+extern char _start[];
+extern char __bss_start[];
+extern char _end[];
+extern char _vmlinux_start[];
+extern char _vmlinux_end[];
+extern char _initrd_start[];
+extern char _initrd_end[];
+extern char _dtb_start[];
+extern char _dtb_end[];
+extern char _esm_blob_start[];
+extern char _esm_blob_end[];
+
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+	int bit;
+	asm ("cntlzw %0,%1" : "=r" (bit) : "r" (n));
+	return 31 - bit;
+}
+
+long partial_decompress(void *inbuf, unsigned long input_size, void *outbuf,
+	unsigned long output_size, unsigned long skip);
+
+#endif /* _PPC_BOOT_OPS_H_ */