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, 278 insertions, 0 deletions

diff --git a/net/ceph/striper.c b/net/ceph/striper.c
new file mode 100644
index 000000000..2b8288858
--- /dev/null
+++ b/net/ceph/striper.c
@@ -0,0 +1,278 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/ceph/ceph_debug.h>
+
+#include <linux/math64.h>
+#include <linux/slab.h>
+
+#include <linux/ceph/striper.h>
+#include <linux/ceph/types.h>
+
+/*
+ * Map a file extent to a stripe unit within an object.
+ * Fill in objno, offset into object, and object extent length (i.e. the
+ * number of bytes mapped, less than or equal to @l->stripe_unit).
+ *
+ * Example for stripe_count = 3, stripes_per_object = 4:
+ *
+ * blockno   |  0  3  6  9 |  1  4  7 10 |  2  5  8 11 | 12 15 18 21 | 13 16 19
+ * stripeno  |  0  1  2  3 |  0  1  2  3 |  0  1  2  3 |  4  5  6  7 |  4  5  6
+ * stripepos |      0      |      1      |      2      |      0      |      1
+ * objno     |      0      |      1      |      2      |      3      |      4
+ * objsetno  |                    0                    |                    1
+ */
+void ceph_calc_file_object_mapping(struct ceph_file_layout *l,
+				   u64 off, u64 len,
+				   u64 *objno, u64 *objoff, u32 *xlen)
+{
+	u32 stripes_per_object = l->object_size / l->stripe_unit;
+	u64 blockno;	/* which su in the file (i.e. globally) */
+	u32 blockoff;	/* offset into su */
+	u64 stripeno;	/* which stripe */
+	u32 stripepos;	/* which su in the stripe,
+			   which object in the object set */
+	u64 objsetno;	/* which object set */
+	u32 objsetpos;	/* which stripe in the object set */
+
+	blockno = div_u64_rem(off, l->stripe_unit, &blockoff);
+	stripeno = div_u64_rem(blockno, l->stripe_count, &stripepos);
+	objsetno = div_u64_rem(stripeno, stripes_per_object, &objsetpos);
+
+	*objno = objsetno * l->stripe_count + stripepos;
+	*objoff = objsetpos * l->stripe_unit + blockoff;
+	*xlen = min_t(u64, len, l->stripe_unit - blockoff);
+}
+EXPORT_SYMBOL(ceph_calc_file_object_mapping);
+
+/*
+ * Return the last extent with given objno (@object_extents is sorted
+ * by objno).  If not found, return NULL and set @add_pos so that the
+ * new extent can be added with list_add(add_pos, new_ex).
+ */
+static struct ceph_object_extent *
+lookup_last(struct list_head *object_extents, u64 objno,
+	    struct list_head **add_pos)
+{
+	struct list_head *pos;
+
+	list_for_each_prev(pos, object_extents) {
+		struct ceph_object_extent *ex =
+		    list_entry(pos, typeof(*ex), oe_item);
+
+		if (ex->oe_objno == objno)
+			return ex;
+
+		if (ex->oe_objno < objno)
+			break;
+	}
+
+	*add_pos = pos;
+	return NULL;
+}
+
+static struct ceph_object_extent *
+lookup_containing(struct list_head *object_extents, u64 objno,
+		  u64 objoff, u32 xlen)
+{
+	struct ceph_object_extent *ex;
+
+	list_for_each_entry(ex, object_extents, oe_item) {
+		if (ex->oe_objno == objno &&
+		    ex->oe_off <= objoff &&
+		    ex->oe_off + ex->oe_len >= objoff + xlen) /* paranoia */
+			return ex;
+
+		if (ex->oe_objno > objno)
+			break;
+	}
+
+	return NULL;
+}
+
+/*
+ * Map a file extent to a sorted list of object extents.
+ *
+ * We want only one (or as few as possible) object extents per object.
+ * Adjacent object extents will be merged together, each returned object
+ * extent may reverse map to multiple different file extents.
+ *
+ * Call @alloc_fn for each new object extent and @action_fn for each
+ * mapped stripe unit, whether it was merged into an already allocated
+ * object extent or started a new object extent.
+ *
+ * Newly allocated object extents are added to @object_extents.
+ * To keep @object_extents sorted, successive calls to this function
+ * must map successive file extents (i.e. the list of file extents that
+ * are mapped using the same @object_extents must be sorted).
+ *
+ * The caller is responsible for @object_extents.
+ */
+int ceph_file_to_extents(struct ceph_file_layout *l, u64 off, u64 len,
+			 struct list_head *object_extents,
+			 struct ceph_object_extent *alloc_fn(void *arg),
+			 void *alloc_arg,
+			 ceph_object_extent_fn_t action_fn,
+			 void *action_arg)
+{
+	struct ceph_object_extent *last_ex, *ex;
+
+	while (len) {
+		struct list_head *add_pos = NULL;
+		u64 objno, objoff;
+		u32 xlen;
+
+		ceph_calc_file_object_mapping(l, off, len, &objno, &objoff,
+					      &xlen);
+
+		last_ex = lookup_last(object_extents, objno, &add_pos);
+		if (!last_ex || last_ex->oe_off + last_ex->oe_len != objoff) {
+			ex = alloc_fn(alloc_arg);
+			if (!ex)
+				return -ENOMEM;
+
+			ex->oe_objno = objno;
+			ex->oe_off = objoff;
+			ex->oe_len = xlen;
+			if (action_fn)
+				action_fn(ex, xlen, action_arg);
+
+			if (!last_ex)
+				list_add(&ex->oe_item, add_pos);
+			else
+				list_add(&ex->oe_item, &last_ex->oe_item);
+		} else {
+			last_ex->oe_len += xlen;
+			if (action_fn)
+				action_fn(last_ex, xlen, action_arg);
+		}
+
+		off += xlen;
+		len -= xlen;
+	}
+
+	for (last_ex = list_first_entry(object_extents, typeof(*ex), oe_item),
+	     ex = list_next_entry(last_ex, oe_item);
+	     &ex->oe_item != object_extents;
+	     last_ex = ex, ex = list_next_entry(ex, oe_item)) {
+		if (last_ex->oe_objno > ex->oe_objno ||
+		    (last_ex->oe_objno == ex->oe_objno &&
+		     last_ex->oe_off + last_ex->oe_len >= ex->oe_off)) {
+			WARN(1, "%s: object_extents list not sorted!\n",
+			     __func__);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(ceph_file_to_extents);
+
+/*
+ * A stripped down, non-allocating version of ceph_file_to_extents(),
+ * for when @object_extents is already populated.
+ */
+int ceph_iterate_extents(struct ceph_file_layout *l, u64 off, u64 len,
+			 struct list_head *object_extents,
+			 ceph_object_extent_fn_t action_fn,
+			 void *action_arg)
+{
+	while (len) {
+		struct ceph_object_extent *ex;
+		u64 objno, objoff;
+		u32 xlen;
+
+		ceph_calc_file_object_mapping(l, off, len, &objno, &objoff,
+					      &xlen);
+
+		ex = lookup_containing(object_extents, objno, objoff, xlen);
+		if (!ex) {
+			WARN(1, "%s: objno %llu %llu~%u not found!\n",
+			     __func__, objno, objoff, xlen);
+			return -EINVAL;
+		}
+
+		action_fn(ex, xlen, action_arg);
+
+		off += xlen;
+		len -= xlen;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(ceph_iterate_extents);
+
+/*
+ * Reverse map an object extent to a sorted list of file extents.
+ *
+ * On success, the caller is responsible for:
+ *
+ *     kfree(file_extents)
+ */
+int ceph_extent_to_file(struct ceph_file_layout *l,
+			u64 objno, u64 objoff, u64 objlen,
+			struct ceph_file_extent **file_extents,
+			u32 *num_file_extents)
+{
+	u32 stripes_per_object = l->object_size / l->stripe_unit;
+	u64 blockno;	/* which su */
+	u32 blockoff;	/* offset into su */
+	u64 stripeno;	/* which stripe */
+	u32 stripepos;	/* which su in the stripe,
+			   which object in the object set */
+	u64 objsetno;	/* which object set */
+	u32 i = 0;
+
+	if (!objlen) {
+		*file_extents = NULL;
+		*num_file_extents = 0;
+		return 0;
+	}
+
+	*num_file_extents = DIV_ROUND_UP_ULL(objoff + objlen, l->stripe_unit) -
+				     DIV_ROUND_DOWN_ULL(objoff, l->stripe_unit);
+	*file_extents = kmalloc_objs(**file_extents, *num_file_extents,
+				     GFP_NOIO);
+	if (!*file_extents)
+		return -ENOMEM;
+
+	div_u64_rem(objoff, l->stripe_unit, &blockoff);
+	while (objlen) {
+		u64 off, len;
+
+		objsetno = div_u64_rem(objno, l->stripe_count, &stripepos);
+		stripeno = div_u64(objoff, l->stripe_unit) +
+						objsetno * stripes_per_object;
+		blockno = stripeno * l->stripe_count + stripepos;
+		off = blockno * l->stripe_unit + blockoff;
+		len = min_t(u64, objlen, l->stripe_unit - blockoff);
+
+		(*file_extents)[i].fe_off = off;
+		(*file_extents)[i].fe_len = len;
+
+		blockoff = 0;
+		objoff += len;
+		objlen -= len;
+		i++;
+	}
+
+	BUG_ON(i != *num_file_extents);
+	return 0;
+}
+EXPORT_SYMBOL(ceph_extent_to_file);
+
+u64 ceph_get_num_objects(struct ceph_file_layout *l, u64 size)
+{
+	u64 period = (u64)l->stripe_count * l->object_size;
+	u64 num_periods = DIV64_U64_ROUND_UP(size, period);
+	u64 remainder_bytes;
+	u64 remainder_objs = 0;
+
+	div64_u64_rem(size, period, &remainder_bytes);
+	if (remainder_bytes > 0 &&
+	    remainder_bytes < (u64)l->stripe_count * l->stripe_unit)
+		remainder_objs = l->stripe_count -
+			    DIV_ROUND_UP_ULL(remainder_bytes, l->stripe_unit);
+
+	return num_periods * l->stripe_count - remainder_objs;
+}
+EXPORT_SYMBOL(ceph_get_num_objects);