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, 293 insertions, 0 deletions

diff --git a/block/partitions/aix.c b/block/partitions/aix.c
new file mode 100644
index 000000000..689837deb
--- /dev/null
+++ b/block/partitions/aix.c
@@ -0,0 +1,293 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/aix.c
+ *
+ *  Copyright (C) 2012-2013 Philippe De Muyter <phdm@macqel.be>
+ */
+
+#include "check.h"
+
+struct lvm_rec {
+	char lvm_id[4]; /* "_LVM" */
+	char reserved4[16];
+	__be32 lvmarea_len;
+	__be32 vgda_len;
+	__be32 vgda_psn[2];
+	char reserved36[10];
+	__be16 pp_size; /* log2(pp_size) */
+	char reserved46[12];
+	__be16 version;
+	};
+
+struct vgda {
+	__be32 secs;
+	__be32 usec;
+	char reserved8[16];
+	__be16 numlvs;
+	__be16 maxlvs;
+	__be16 pp_size;
+	__be16 numpvs;
+	__be16 total_vgdas;
+	__be16 vgda_size;
+	};
+
+struct lvd {
+	__be16 lv_ix;
+	__be16 res2;
+	__be16 res4;
+	__be16 maxsize;
+	__be16 lv_state;
+	__be16 mirror;
+	__be16 mirror_policy;
+	__be16 num_lps;
+	__be16 res10[8];
+	};
+
+struct lvname {
+	char name[64];
+	};
+
+struct ppe {
+	__be16 lv_ix;
+	unsigned short res2;
+	unsigned short res4;
+	__be16 lp_ix;
+	unsigned short res8[12];
+	};
+
+struct pvd {
+	char reserved0[16];
+	__be16 pp_count;
+	char reserved18[2];
+	__be32 psn_part1;
+	char reserved24[8];
+	struct ppe ppe[1016];
+	};
+
+#define LVM_MAXLVS 256
+
+/**
+ * read_lba(): Read bytes from disk, starting at given LBA
+ * @state
+ * @lba
+ * @buffer
+ * @count
+ *
+ * Description:  Reads @count bytes from @state->disk into @buffer.
+ * Returns number of bytes read on success, 0 on error.
+ */
+static size_t read_lba(struct parsed_partitions *state, u64 lba, u8 *buffer,
+			size_t count)
+{
+	size_t totalreadcount = 0;
+
+	if (!buffer || lba + count / 512 > get_capacity(state->disk) - 1ULL)
+		return 0;
+
+	while (count) {
+		int copied = 512;
+		Sector sect;
+		unsigned char *data = read_part_sector(state, lba++, &sect);
+		if (!data)
+			break;
+		if (copied > count)
+			copied = count;
+		memcpy(buffer, data, copied);
+		put_dev_sector(sect);
+		buffer += copied;
+		totalreadcount += copied;
+		count -= copied;
+	}
+	return totalreadcount;
+}
+
+/**
+ * alloc_pvd(): reads physical volume descriptor
+ * @state
+ * @lba
+ *
+ * Description: Returns pvd on success,  NULL on error.
+ * Allocates space for pvd and fill it with disk blocks at @lba
+ * Notes: remember to free pvd when you're done!
+ */
+static struct pvd *alloc_pvd(struct parsed_partitions *state, u32 lba)
+{
+	size_t count = sizeof(struct pvd);
+	struct pvd *p;
+
+	p = kmalloc(count, GFP_KERNEL);
+	if (!p)
+		return NULL;
+
+	if (read_lba(state, lba, (u8 *) p, count) < count) {
+		kfree(p);
+		return NULL;
+	}
+	return p;
+}
+
+/**
+ * alloc_lvn(): reads logical volume names
+ * @state
+ * @lba
+ *
+ * Description: Returns lvn on success,  NULL on error.
+ * Allocates space for lvn and fill it with disk blocks at @lba
+ * Notes: remember to free lvn when you're done!
+ */
+static struct lvname *alloc_lvn(struct parsed_partitions *state, u32 lba)
+{
+	size_t count = sizeof(struct lvname) * LVM_MAXLVS;
+	struct lvname *p;
+
+	p = kmalloc(count, GFP_KERNEL);
+	if (!p)
+		return NULL;
+
+	if (read_lba(state, lba, (u8 *) p, count) < count) {
+		kfree(p);
+		return NULL;
+	}
+	return p;
+}
+
+int aix_partition(struct parsed_partitions *state)
+{
+	int ret = 0;
+	Sector sect;
+	unsigned char *d;
+	u32 pp_bytes_size;
+	u32 pp_blocks_size = 0;
+	u32 vgda_sector = 0;
+	u32 vgda_len = 0;
+	int numlvs = 0;
+	struct pvd *pvd = NULL;
+	struct lv_info {
+		unsigned short pps_per_lv;
+		unsigned short pps_found;
+		unsigned char lv_is_contiguous;
+	} *lvip;
+	struct lvname *n = NULL;
+
+	d = read_part_sector(state, 7, &sect);
+	if (d) {
+		struct lvm_rec *p = (struct lvm_rec *)d;
+		u16 lvm_version = be16_to_cpu(p->version);
+
+		if (lvm_version == 1) {
+			int pp_size_log2 = be16_to_cpu(p->pp_size);
+
+			pp_bytes_size = 1 << pp_size_log2;
+			pp_blocks_size = pp_bytes_size / 512;
+			seq_buf_printf(&state->pp_buf,
+				       " AIX LVM header version %u found\n",
+				       lvm_version);
+			vgda_len = be32_to_cpu(p->vgda_len);
+			vgda_sector = be32_to_cpu(p->vgda_psn[0]);
+		} else {
+			seq_buf_printf(&state->pp_buf,
+				       " unsupported AIX LVM version %d found\n",
+				       lvm_version);
+		}
+		put_dev_sector(sect);
+	}
+	if (vgda_sector && (d = read_part_sector(state, vgda_sector, &sect))) {
+		struct vgda *p = (struct vgda *)d;
+
+		numlvs = be16_to_cpu(p->numlvs);
+		put_dev_sector(sect);
+	}
+	lvip = kzalloc_objs(struct lv_info, state->limit);
+	if (!lvip)
+		return 0;
+	if (numlvs && (d = read_part_sector(state, vgda_sector + 1, &sect))) {
+		struct lvd *p = (struct lvd *)d;
+		int i;
+
+		n = alloc_lvn(state, vgda_sector + vgda_len - 33);
+		if (n) {
+			int foundlvs = 0;
+
+			/*
+			 * The lvd array was read as a single sector; only the
+			 * struct lvd entries that fit in it are valid.  Bound the
+			 * scan so an on-disk numlvs larger than that cannot walk
+			 * the read buffer out of bounds.
+			 */
+			for (i = 0; foundlvs < numlvs && i < state->limit &&
+				    i < SECTOR_SIZE / (int)sizeof(struct lvd); i++) {
+				lvip[i].pps_per_lv = be16_to_cpu(p[i].num_lps);
+				if (lvip[i].pps_per_lv)
+					foundlvs += 1;
+			}
+			/* pvd loops depend on n[].name and lvip[].pps_per_lv */
+			pvd = alloc_pvd(state, vgda_sector + 17);
+		}
+		put_dev_sector(sect);
+	}
+	if (pvd) {
+		int numpps = be16_to_cpu(pvd->pp_count);
+		int psn_part1 = be32_to_cpu(pvd->psn_part1);
+		int i;
+		int cur_lv_ix = -1;
+		int next_lp_ix = 1;
+		int lp_ix;
+
+		/*
+		 * pvd was read into a fixed-size struct pvd whose ppe[] array
+		 * holds ARRAY_SIZE(pvd->ppe) entries.  pp_count is an
+		 * unvalidated on-disk __be16, so clamp the scan to the array
+		 * size to avoid walking past the allocation.
+		 */
+		if (numpps > ARRAY_SIZE(pvd->ppe))
+			numpps = ARRAY_SIZE(pvd->ppe);
+
+		for (i = 0; i < numpps; i += 1) {
+			struct ppe *p = pvd->ppe + i;
+			unsigned int lv_ix;
+
+			lp_ix = be16_to_cpu(p->lp_ix);
+			if (!lp_ix) {
+				next_lp_ix = 1;
+				continue;
+			}
+			lv_ix = be16_to_cpu(p->lv_ix) - 1;
+			if (lv_ix >= state->limit) {
+				cur_lv_ix = -1;
+				continue;
+			}
+			lvip[lv_ix].pps_found += 1;
+			if (lp_ix == 1) {
+				cur_lv_ix = lv_ix;
+				next_lp_ix = 1;
+			} else if (lv_ix != cur_lv_ix || lp_ix != next_lp_ix) {
+				next_lp_ix = 1;
+				continue;
+			}
+			if (lp_ix == lvip[lv_ix].pps_per_lv) {
+				put_partition(state, lv_ix + 1,
+				  (i + 1 - lp_ix) * pp_blocks_size + psn_part1,
+				  lvip[lv_ix].pps_per_lv * pp_blocks_size);
+				seq_buf_printf(&state->pp_buf, " <%s>\n",
+					       n[lv_ix].name);
+				lvip[lv_ix].lv_is_contiguous = 1;
+				ret = 1;
+				next_lp_ix = 1;
+			} else
+				next_lp_ix += 1;
+		}
+		for (i = 0; i < state->limit; i += 1)
+			if (lvip[i].pps_found && !lvip[i].lv_is_contiguous) {
+				char tmp[sizeof(n[i].name) + 1]; // null char
+
+				snprintf(tmp, sizeof(tmp), "%s", n[i].name);
+				pr_warn("partition %s (%u pp's found) is "
+					"not contiguous\n",
+					tmp, lvip[i].pps_found);
+			}
+		kfree(pvd);
+	}
+	kfree(n);
+	kfree(lvip);
+	return ret;
+}