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, 215 insertions, 0 deletions

diff --git a/include/trace/events/erofs.h b/include/trace/events/erofs.h
new file mode 100644
index 000000000..0a178cb10
--- /dev/null
+++ b/include/trace/events/erofs.h
@@ -0,0 +1,215 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM erofs
+
+#if !defined(_TRACE_EROFS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_EROFS_H
+
+#include <linux/tracepoint.h>
+#include <linux/fs.h>
+
+struct erofs_map_blocks;
+
+#define show_dev(dev)		MAJOR(dev), MINOR(dev)
+#define show_dev_nid(entry)	show_dev(entry->dev), entry->nid
+
+#define show_file_type(type)						\
+	__print_symbolic(type,						\
+		{ 0,		"FILE" },				\
+		{ 1,		"DIR" })
+
+#define show_map_flags(flags) __print_flags(flags, "|",	\
+	{ EROFS_GET_BLOCKS_FIEMAP,	"FIEMAP" },	\
+	{ EROFS_GET_BLOCKS_READMORE,	"READMORE" },	\
+	{ EROFS_GET_BLOCKS_FINDTAIL,	"FINDTAIL" })
+
+#define show_mflags(flags) __print_flags(flags, "",	\
+	{ EROFS_MAP_MAPPED,		"M" },		\
+	{ EROFS_MAP_META,		"I" },		\
+	{ EROFS_MAP_PARTIAL_MAPPED,	"T" },		\
+	{ EROFS_MAP_PARTIAL_REF,	"P" },		\
+	{ EROFS_MAP_FRAGMENT,		"R" })
+
+TRACE_EVENT(erofs_lookup,
+
+	TP_PROTO(struct inode *dir, struct dentry *dentry, unsigned int flags),
+
+	TP_ARGS(dir, dentry, flags),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev	)
+		__field(erofs_nid_t,	nid	)
+		__string(name,		dentry->d_name.name	)
+		__field(unsigned int,	flags	)
+	),
+
+	TP_fast_assign(
+		__entry->dev	= dir->i_sb->s_dev;
+		__entry->nid	= EROFS_I(dir)->nid;
+		__assign_str(name);
+		__entry->flags	= flags;
+	),
+
+	TP_printk("dev = (%d,%d), pnid = %llu, name:%s, flags:%x",
+		show_dev_nid(__entry),
+		__get_str(name),
+		__entry->flags)
+);
+
+TRACE_EVENT(erofs_fill_inode,
+	TP_PROTO(struct inode *inode),
+	TP_ARGS(inode),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev	)
+		__field(erofs_nid_t,	nid	)
+		__field(erofs_blk_t,	blkaddr )
+		__field(unsigned int,	ofs	)
+	),
+
+	TP_fast_assign(
+		__entry->dev		= inode->i_sb->s_dev;
+		__entry->nid		= EROFS_I(inode)->nid;
+		__entry->blkaddr	= erofs_blknr(inode->i_sb, erofs_iloc(inode));
+		__entry->ofs		= erofs_blkoff(inode->i_sb, erofs_iloc(inode));
+	),
+
+	TP_printk("dev = (%d,%d), nid = %llu, blkaddr %llu ofs %u",
+		  show_dev_nid(__entry),
+		  __entry->blkaddr, __entry->ofs)
+);
+
+TRACE_EVENT(erofs_read_folio,
+
+	TP_PROTO(struct inode *inode, struct folio *folio, bool raw),
+
+	TP_ARGS(inode, folio, raw),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev	)
+		__field(erofs_nid_t,    nid     )
+		__field(int,		dir	)
+		__field(pgoff_t,	index	)
+		__field(unsigned int,	order	)
+		__field(bool,		raw	)
+	),
+
+	TP_fast_assign(
+		__entry->dev	= inode->i_sb->s_dev;
+		__entry->nid	= EROFS_I(inode)->nid;
+		__entry->dir	= S_ISDIR(inode->i_mode);
+		__entry->index	= folio->index;
+		__entry->order	= folio_order(folio);
+		__entry->raw = raw;
+	),
+
+	TP_printk("dev = (%d,%d), nid = %llu, %s, index = %lu, order = %u, raw = %d",
+		show_dev_nid(__entry),
+		show_file_type(__entry->dir),
+		(unsigned long)__entry->index,
+		__entry->order,
+		__entry->raw)
+);
+
+TRACE_EVENT(erofs_readahead,
+
+	TP_PROTO(struct inode *inode, pgoff_t start, unsigned int nrpage,
+		bool raw),
+
+	TP_ARGS(inode, start, nrpage, raw),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev	)
+		__field(erofs_nid_t,	nid	)
+		__field(pgoff_t,	start	)
+		__field(unsigned int,	nrpage	)
+		__field(bool,		raw	)
+	),
+
+	TP_fast_assign(
+		__entry->dev	= inode->i_sb->s_dev;
+		__entry->nid	= EROFS_I(inode)->nid;
+		__entry->start	= start;
+		__entry->nrpage	= nrpage;
+		__entry->raw	= raw;
+	),
+
+	TP_printk("dev = (%d,%d), nid = %llu, start = %lu nrpage = %u raw = %d",
+		show_dev_nid(__entry),
+		(unsigned long)__entry->start,
+		__entry->nrpage,
+		__entry->raw)
+);
+
+TRACE_EVENT(erofs_map_blocks_enter,
+
+	TP_PROTO(struct inode *inode, struct erofs_map_blocks *map,
+		 unsigned int flags),
+
+	TP_ARGS(inode, map, flags),
+
+	TP_STRUCT__entry(
+		__field(	dev_t,		dev		)
+		__field(	erofs_nid_t,	nid		)
+		__field(	erofs_off_t,	la		)
+		__field(	u64,		llen		)
+		__field(	unsigned int,	flags		)
+	),
+
+	TP_fast_assign(
+		__entry->dev    = inode->i_sb->s_dev;
+		__entry->nid    = EROFS_I(inode)->nid;
+		__entry->la	= map->m_la;
+		__entry->llen	= map->m_llen;
+		__entry->flags	= flags;
+	),
+
+	TP_printk("dev = (%d,%d), nid = %llu, la %llu llen %llu flags %s",
+		  show_dev_nid(__entry),
+		  __entry->la, __entry->llen,
+		  __entry->flags ? show_map_flags(__entry->flags) : "NULL")
+);
+
+TRACE_EVENT(erofs_map_blocks_exit,
+
+	TP_PROTO(struct inode *inode, struct erofs_map_blocks *map,
+		 unsigned int flags, int ret),
+
+	TP_ARGS(inode, map, flags, ret),
+
+	TP_STRUCT__entry(
+		__field(	dev_t,		dev		)
+		__field(	erofs_nid_t,	nid		)
+		__field(        unsigned int,   flags           )
+		__field(	erofs_off_t,	la		)
+		__field(	erofs_off_t,	pa		)
+		__field(	u64,		llen		)
+		__field(	u64,		plen		)
+		__field(        unsigned int,	mflags		)
+		__field(	int,		ret		)
+	),
+
+	TP_fast_assign(
+		__entry->dev    = inode->i_sb->s_dev;
+		__entry->nid    = EROFS_I(inode)->nid;
+		__entry->flags	= flags;
+		__entry->la	= map->m_la;
+		__entry->pa	= map->m_pa;
+		__entry->llen	= map->m_llen;
+		__entry->plen	= map->m_plen;
+		__entry->mflags	= map->m_flags;
+		__entry->ret	= ret;
+	),
+
+	TP_printk("dev = (%d,%d), nid = %llu, flags %s "
+		  "la %llu pa %llu llen %llu plen %llu mflags %s ret %d",
+		  show_dev_nid(__entry),
+		  __entry->flags ? show_map_flags(__entry->flags) : "NULL",
+		  __entry->la, __entry->pa, __entry->llen, __entry->plen,
+		  show_mflags(__entry->mflags), __entry->ret)
+);
+
+#endif /* _TRACE_EROFS_H */
+
+ /* This part must be outside protection */
+#include <trace/define_trace.h>