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, 208 insertions, 0 deletions

diff --git a/fs/coda/coda_linux.c b/fs/coda/coda_linux.c
new file mode 100644
index 000000000..1d2dac95f
--- /dev/null
+++ b/fs/coda/coda_linux.c
@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Inode operations for Coda filesystem
+ * Original version: (C) 1996 P. Braam and M. Callahan
+ * Rewritten for Linux 2.1. (C) 1997 Carnegie Mellon University
+ * 
+ * Carnegie Mellon encourages users to contribute improvements to
+ * the Coda project. Contact Peter Braam (coda@cs.cmu.edu).
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/fs.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+#include <linux/string.h>
+
+#include <linux/coda.h>
+#include "coda_psdev.h"
+#include "coda_linux.h"
+
+/* initialize the debugging variables */
+int coda_fake_statfs;
+
+/* print a fid */
+char * coda_f2s(struct CodaFid *f)
+{
+	static char s[60];
+
+ 	sprintf(s, "(%08x.%08x.%08x.%08x)", f->opaque[0], f->opaque[1], f->opaque[2], f->opaque[3]);
+
+	return s;
+}
+
+/* recognize special .CONTROL name */
+int coda_iscontrol(const char *name, size_t length)
+{
+	return ((CODA_CONTROLLEN == length) && 
+                (strncmp(name, CODA_CONTROL, CODA_CONTROLLEN) == 0));
+}
+
+unsigned short coda_flags_to_cflags(unsigned short flags)
+{
+	unsigned short coda_flags = 0;
+	
+	if ((flags & O_ACCMODE) == O_RDONLY)
+		coda_flags |= C_O_READ;
+
+	if ((flags & O_ACCMODE) == O_RDWR)
+		coda_flags |= C_O_READ | C_O_WRITE;
+
+	if ((flags & O_ACCMODE) == O_WRONLY)
+		coda_flags |= C_O_WRITE;
+
+	if (flags & O_TRUNC)
+		coda_flags |= C_O_TRUNC;
+
+	if (flags & O_CREAT)
+		coda_flags |= C_O_CREAT;
+
+	if (flags & O_EXCL)
+		coda_flags |= C_O_EXCL;
+
+	return coda_flags;
+}
+
+static struct timespec64 coda_to_timespec64(struct coda_timespec ts)
+{
+	struct timespec64 ts64 = {
+		.tv_sec = ts.tv_sec,
+		.tv_nsec = ts.tv_nsec,
+	};
+
+	return ts64;
+}
+
+static struct coda_timespec timespec64_to_coda(struct timespec64 ts64)
+{
+	struct coda_timespec ts = {
+		.tv_sec = ts64.tv_sec,
+		.tv_nsec = ts64.tv_nsec,
+	};
+
+	return ts;
+}
+
+/* utility functions below */
+umode_t coda_inode_type(struct coda_vattr *attr)
+{
+	switch (attr->va_type) {
+	case C_VREG:
+		return S_IFREG;
+	case C_VDIR:
+		return S_IFDIR;
+	case C_VLNK:
+		return S_IFLNK;
+	case C_VNON:
+	default:
+		return 0;
+	}
+}
+
+void coda_vattr_to_iattr(struct inode *inode, struct coda_vattr *attr)
+{
+	/* inode's i_flags, i_ino are set by iget
+	 * XXX: is this all we need ??
+	 */
+	umode_t inode_type = coda_inode_type(attr);
+	inode->i_mode |= inode_type;
+
+	if (attr->va_mode != (u_short) -1)
+	        inode->i_mode = attr->va_mode | inode_type;
+        if (attr->va_uid != -1) 
+	        inode->i_uid = make_kuid(&init_user_ns, (uid_t) attr->va_uid);
+        if (attr->va_gid != -1)
+	        inode->i_gid = make_kgid(&init_user_ns, (gid_t) attr->va_gid);
+	if (attr->va_nlink != -1)
+		set_nlink(inode, attr->va_nlink);
+	if (attr->va_size != -1)
+	        inode->i_size = attr->va_size;
+	if (attr->va_size != -1)
+		inode->i_blocks = (attr->va_size + 511) >> 9;
+	if (attr->va_atime.tv_sec != -1) 
+		inode_set_atime_to_ts(inode,
+				      coda_to_timespec64(attr->va_atime));
+	if (attr->va_mtime.tv_sec != -1)
+		inode_set_mtime_to_ts(inode,
+				      coda_to_timespec64(attr->va_mtime));
+        if (attr->va_ctime.tv_sec != -1)
+		inode_set_ctime_to_ts(inode,
+				      coda_to_timespec64(attr->va_ctime));
+}
+
+
+/* 
+ * BSD sets attributes that need not be modified to -1. 
+ * Linux uses the valid field to indicate what should be
+ * looked at.  The BSD type field needs to be deduced from linux 
+ * mode.
+ * So we have to do some translations here.
+ */
+
+void coda_iattr_to_vattr(struct iattr *iattr, struct coda_vattr *vattr)
+{
+        unsigned int valid;
+
+        /* clean out */        
+	vattr->va_mode = -1;
+        vattr->va_uid = (vuid_t) -1; 
+        vattr->va_gid = (vgid_t) -1;
+        vattr->va_size = (off_t) -1;
+	vattr->va_atime.tv_sec = (int64_t) -1;
+	vattr->va_atime.tv_nsec = (long) -1;
+	vattr->va_mtime.tv_sec = (int64_t) -1;
+	vattr->va_mtime.tv_nsec = (long) -1;
+	vattr->va_ctime.tv_sec = (int64_t) -1;
+	vattr->va_ctime.tv_nsec = (long) -1;
+        vattr->va_type = C_VNON;
+	vattr->va_fileid = -1;
+	vattr->va_gen = -1;
+	vattr->va_bytes = -1;
+	vattr->va_nlink = -1;
+	vattr->va_blocksize = -1;
+	vattr->va_rdev = -1;
+        vattr->va_flags = 0;
+
+        /* determine the type */
+#if 0
+        mode = iattr->ia_mode;
+                if ( S_ISDIR(mode) ) {
+                vattr->va_type = C_VDIR; 
+        } else if ( S_ISREG(mode) ) {
+                vattr->va_type = C_VREG;
+        } else if ( S_ISLNK(mode) ) {
+                vattr->va_type = C_VLNK;
+        } else {
+                /* don't do others */
+                vattr->va_type = C_VNON;
+        }
+#endif 
+
+        /* set those vattrs that need change */
+        valid = iattr->ia_valid;
+        if ( valid & ATTR_MODE ) {
+                vattr->va_mode = iattr->ia_mode;
+	}
+        if ( valid & ATTR_UID ) {
+                vattr->va_uid = (vuid_t) from_kuid(&init_user_ns, iattr->ia_uid);
+	}
+        if ( valid & ATTR_GID ) {
+                vattr->va_gid = (vgid_t) from_kgid(&init_user_ns, iattr->ia_gid);
+	}
+        if ( valid & ATTR_SIZE ) {
+                vattr->va_size = iattr->ia_size;
+	}
+        if ( valid & ATTR_ATIME ) {
+		vattr->va_atime = timespec64_to_coda(iattr->ia_atime);
+	}
+        if ( valid & ATTR_MTIME ) {
+		vattr->va_mtime = timespec64_to_coda(iattr->ia_mtime);
+	}
+        if ( valid & ATTR_CTIME ) {
+		vattr->va_ctime = timespec64_to_coda(iattr->ia_ctime);
+	}
+}
+