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, 73 insertions, 0 deletions

diff --git a/include/uapi/asm-generic/stat.h b/include/uapi/asm-generic/stat.h
new file mode 100644
index 000000000..0d962ecd1
--- /dev/null
+++ b/include/uapi/asm-generic/stat.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __ASM_GENERIC_STAT_H
+#define __ASM_GENERIC_STAT_H
+
+/*
+ * Everybody gets this wrong and has to stick with it for all
+ * eternity. Hopefully, this version gets used by new architectures
+ * so they don't fall into the same traps.
+ *
+ * stat64 is copied from powerpc64, with explicit padding added.
+ * stat is the same structure layout on 64-bit, without the 'long long'
+ * types.
+ *
+ * By convention, 64 bit architectures use the stat interface, while
+ * 32 bit architectures use the stat64 interface. Note that we don't
+ * provide an __old_kernel_stat here, which new architecture should
+ * not have to start with.
+ */
+
+#include <asm/bitsperlong.h>
+
+#define STAT_HAVE_NSEC 1
+
+struct stat {
+	unsigned long	st_dev;		/* Device.  */
+	unsigned long	st_ino;		/* File serial number.  */
+	unsigned int	st_mode;	/* File mode.  */
+	unsigned int	st_nlink;	/* Link count.  */
+	unsigned int	st_uid;		/* User ID of the file's owner.  */
+	unsigned int	st_gid;		/* Group ID of the file's group. */
+	unsigned long	st_rdev;	/* Device number, if device.  */
+	unsigned long	__pad1;
+	long		st_size;	/* Size of file, in bytes.  */
+	int		st_blksize;	/* Optimal block size for I/O.  */
+	int		__pad2;
+	long		st_blocks;	/* Number 512-byte blocks allocated. */
+	long		st_atime;	/* Time of last access.  */
+	unsigned long	st_atime_nsec;
+	long		st_mtime;	/* Time of last modification.  */
+	unsigned long	st_mtime_nsec;
+	long		st_ctime;	/* Time of last status change.  */
+	unsigned long	st_ctime_nsec;
+	unsigned int	__unused4;
+	unsigned int	__unused5;
+};
+
+/* This matches struct stat64 in glibc2.1. Only used for 32 bit. */
+#if __BITS_PER_LONG != 64 || defined(__ARCH_WANT_STAT64)
+struct stat64 {
+	unsigned long long st_dev;	/* Device.  */
+	unsigned long long st_ino;	/* File serial number.  */
+	unsigned int	st_mode;	/* File mode.  */
+	unsigned int	st_nlink;	/* Link count.  */
+	unsigned int	st_uid;		/* User ID of the file's owner.  */
+	unsigned int	st_gid;		/* Group ID of the file's group. */
+	unsigned long long st_rdev;	/* Device number, if device.  */
+	unsigned long long __pad1;
+	long long	st_size;	/* Size of file, in bytes.  */
+	int		st_blksize;	/* Optimal block size for I/O.  */
+	int		__pad2;
+	long long	st_blocks;	/* Number 512-byte blocks allocated. */
+	int		st_atime;	/* Time of last access.  */
+	unsigned int	st_atime_nsec;
+	int		st_mtime;	/* Time of last modification.  */
+	unsigned int	st_mtime_nsec;
+	int		st_ctime;	/* Time of last status change.  */
+	unsigned int	st_ctime_nsec;
+	unsigned int	__unused4;
+	unsigned int	__unused5;
+};
+#endif
+
+#endif /* __ASM_GENERIC_STAT_H */