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, 169 insertions, 0 deletions

diff --git a/fs/hfsplus/options.c b/fs/hfsplus/options.c
new file mode 100644
index 000000000..9b377481f
--- /dev/null
+++ b/fs/hfsplus/options.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/hfsplus/options.c
+ *
+ * Copyright (C) 2001
+ * Brad Boyer (flar@allandria.com)
+ * (C) 2003 Ardis Technologies <roman@ardistech.com>
+ *
+ * Option parsing
+ */
+
+#include <linux/string.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/fs_struct.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/nls.h>
+#include <linux/mount.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include "hfsplus_fs.h"
+
+enum {
+	opt_creator, opt_type,
+	opt_umask, opt_uid, opt_gid,
+	opt_part, opt_session, opt_nls,
+	opt_decompose, opt_barrier,
+	opt_force,
+};
+
+static const struct fs_parameter_spec hfs_param_spec[] = {
+	fsparam_string	("creator",	opt_creator),
+	fsparam_string	("type",	opt_type),
+	fsparam_u32oct	("umask",	opt_umask),
+	fsparam_u32	("uid",		opt_uid),
+	fsparam_u32	("gid",		opt_gid),
+	fsparam_u32	("part",	opt_part),
+	fsparam_u32	("session",	opt_session),
+	fsparam_string	("nls",		opt_nls),
+	fsparam_flag_no	("decompose",	opt_decompose),
+	fsparam_flag_no	("barrier",	opt_barrier),
+	fsparam_flag	("force",	opt_force),
+	{}
+};
+
+/* Initialize an options object to reasonable defaults */
+void hfsplus_fill_defaults(struct hfsplus_sb_info *opts)
+{
+	if (!opts)
+		return;
+
+	opts->creator = HFSPLUS_DEF_CR_TYPE;
+	opts->type = HFSPLUS_DEF_CR_TYPE;
+	opts->umask = current_umask();
+	opts->uid = current_uid();
+	opts->gid = current_gid();
+	opts->part = -1;
+	opts->session = -1;
+}
+
+/* Parse options from mount. Returns nonzero errno on failure */
+int hfsplus_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct hfsplus_sb_info *sbi = fc->s_fs_info;
+	struct fs_parse_result result;
+	int opt;
+
+	/*
+	 * Only the force option is examined during remount, all others
+	 * are ignored.
+	 */
+	if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE &&
+	    strncmp(param->key, "force", 5))
+		return 0;
+
+	opt = fs_parse(fc, hfs_param_spec, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case opt_creator:
+		if (strlen(param->string) != 4) {
+			pr_err("creator requires a 4 character value\n");
+			return -EINVAL;
+		}
+		memcpy(&sbi->creator, param->string, 4);
+		break;
+	case opt_type:
+		if (strlen(param->string) != 4) {
+			pr_err("type requires a 4 character value\n");
+			return -EINVAL;
+		}
+		memcpy(&sbi->type, param->string, 4);
+		break;
+	case opt_umask:
+		sbi->umask = (umode_t)result.uint_32;
+		break;
+	case opt_uid:
+		sbi->uid = result.uid;
+		set_bit(HFSPLUS_SB_UID, &sbi->flags);
+		break;
+	case opt_gid:
+		sbi->gid = result.gid;
+		set_bit(HFSPLUS_SB_GID, &sbi->flags);
+		break;
+	case opt_part:
+		sbi->part = result.uint_32;
+		break;
+	case opt_session:
+		sbi->session = result.uint_32;
+		break;
+	case opt_nls:
+		if (sbi->nls) {
+			pr_err("unable to change nls mapping\n");
+			return -EINVAL;
+		}
+		sbi->nls = load_nls(param->string);
+		if (!sbi->nls) {
+			pr_err("unable to load nls mapping \"%s\"\n",
+			       param->string);
+			return -EINVAL;
+		}
+		break;
+	case opt_decompose:
+		if (result.negated)
+			set_bit(HFSPLUS_SB_NODECOMPOSE, &sbi->flags);
+		else
+			clear_bit(HFSPLUS_SB_NODECOMPOSE, &sbi->flags);
+		break;
+	case opt_barrier:
+		if (result.negated)
+			set_bit(HFSPLUS_SB_NOBARRIER, &sbi->flags);
+		else
+			clear_bit(HFSPLUS_SB_NOBARRIER, &sbi->flags);
+		break;
+	case opt_force:
+		set_bit(HFSPLUS_SB_FORCE, &sbi->flags);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+int hfsplus_show_options(struct seq_file *seq, struct dentry *root)
+{
+	struct hfsplus_sb_info *sbi = HFSPLUS_SB(root->d_sb);
+
+	if (sbi->creator != HFSPLUS_DEF_CR_TYPE)
+		seq_show_option_n(seq, "creator", (char *)&sbi->creator, 4);
+	if (sbi->type != HFSPLUS_DEF_CR_TYPE)
+		seq_show_option_n(seq, "type", (char *)&sbi->type, 4);
+	seq_printf(seq, ",umask=%o,uid=%u,gid=%u", sbi->umask,
+			from_kuid_munged(&init_user_ns, sbi->uid),
+			from_kgid_munged(&init_user_ns, sbi->gid));
+	if (sbi->part >= 0)
+		seq_printf(seq, ",part=%u", sbi->part);
+	if (sbi->session >= 0)
+		seq_printf(seq, ",session=%u", sbi->session);
+	if (sbi->nls)
+		seq_printf(seq, ",nls=%s", sbi->nls->charset);
+	if (test_bit(HFSPLUS_SB_NODECOMPOSE, &sbi->flags))
+		seq_puts(seq, ",nodecompose");
+	if (test_bit(HFSPLUS_SB_NOBARRIER, &sbi->flags))
+		seq_puts(seq, ",nobarrier");
+	return 0;
+}