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, 228 insertions, 0 deletions

diff --git a/fs/jffs2/read.c b/fs/jffs2/read.c
new file mode 100644
index 000000000..0b042b1fc
--- /dev/null
+++ b/fs/jffs2/read.c
@@ -0,0 +1,228 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/crc32.h>
+#include <linux/pagemap.h>
+#include <linux/mtd/mtd.h>
+#include <linux/compiler.h>
+#include "nodelist.h"
+#include "compr.h"
+
+int jffs2_read_dnode(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+		     struct jffs2_full_dnode *fd, unsigned char *buf,
+		     int ofs, int len)
+{
+	struct jffs2_raw_inode *ri;
+	size_t readlen;
+	uint32_t crc;
+	unsigned char *decomprbuf = NULL;
+	unsigned char *readbuf = NULL;
+	int ret = 0;
+
+	ri = jffs2_alloc_raw_inode();
+	if (!ri)
+		return -ENOMEM;
+
+	ret = jffs2_flash_read(c, ref_offset(fd->raw), sizeof(*ri), &readlen, (char *)ri);
+	if (ret) {
+		jffs2_free_raw_inode(ri);
+		pr_warn("Error reading node from 0x%08x: %d\n",
+			ref_offset(fd->raw), ret);
+		return ret;
+	}
+	if (readlen != sizeof(*ri)) {
+		jffs2_free_raw_inode(ri);
+		pr_warn("Short read from 0x%08x: wanted 0x%zx bytes, got 0x%zx\n",
+			ref_offset(fd->raw), sizeof(*ri), readlen);
+		return -EIO;
+	}
+	crc = crc32(0, ri, sizeof(*ri)-8);
+
+	jffs2_dbg(1, "Node read from %08x: node_crc %08x, calculated CRC %08x. dsize %x, csize %x, offset %x, buf %p\n",
+		  ref_offset(fd->raw), je32_to_cpu(ri->node_crc),
+		  crc, je32_to_cpu(ri->dsize), je32_to_cpu(ri->csize),
+		  je32_to_cpu(ri->offset), buf);
+	if (crc != je32_to_cpu(ri->node_crc)) {
+		pr_warn("Node CRC %08x != calculated CRC %08x for node at %08x\n",
+			je32_to_cpu(ri->node_crc), crc, ref_offset(fd->raw));
+		ret = -EIO;
+		goto out_ri;
+	}
+	/* There was a bug where we wrote hole nodes out with csize/dsize
+	   swapped. Deal with it */
+	if (ri->compr == JFFS2_COMPR_ZERO && !je32_to_cpu(ri->dsize) &&
+	    je32_to_cpu(ri->csize)) {
+		ri->dsize = ri->csize;
+		ri->csize = cpu_to_je32(0);
+	}
+
+	D1(if(ofs + len > je32_to_cpu(ri->dsize)) {
+			pr_warn("jffs2_read_dnode() asked for %d bytes at %d from %d-byte node\n",
+				len, ofs, je32_to_cpu(ri->dsize));
+		ret = -EINVAL;
+		goto out_ri;
+	});
+
+
+	if (ri->compr == JFFS2_COMPR_ZERO) {
+		memset(buf, 0, len);
+		goto out_ri;
+	}
+
+	/* Cases:
+	   Reading whole node and it's uncompressed - read directly to buffer provided, check CRC.
+	   Reading whole node and it's compressed - read into comprbuf, check CRC and decompress to buffer provided
+	   Reading partial node and it's uncompressed - read into readbuf, check CRC, and copy
+	   Reading partial node and it's compressed - read into readbuf, check checksum, decompress to decomprbuf and copy
+	*/
+	if (ri->compr == JFFS2_COMPR_NONE && len == je32_to_cpu(ri->dsize)) {
+		readbuf = buf;
+	} else {
+		readbuf = kmalloc(je32_to_cpu(ri->csize), GFP_KERNEL);
+		if (!readbuf) {
+			ret = -ENOMEM;
+			goto out_ri;
+		}
+	}
+	if (ri->compr != JFFS2_COMPR_NONE) {
+		if (len < je32_to_cpu(ri->dsize)) {
+			decomprbuf = kmalloc(je32_to_cpu(ri->dsize), GFP_KERNEL);
+			if (!decomprbuf) {
+				ret = -ENOMEM;
+				goto out_readbuf;
+			}
+		} else {
+			decomprbuf = buf;
+		}
+	} else {
+		decomprbuf = readbuf;
+	}
+
+	jffs2_dbg(2, "Read %d bytes to %p\n", je32_to_cpu(ri->csize),
+		  readbuf);
+	ret = jffs2_flash_read(c, (ref_offset(fd->raw)) + sizeof(*ri),
+			       je32_to_cpu(ri->csize), &readlen, readbuf);
+
+	if (!ret && readlen != je32_to_cpu(ri->csize))
+		ret = -EIO;
+	if (ret)
+		goto out_decomprbuf;
+
+	crc = crc32(0, readbuf, je32_to_cpu(ri->csize));
+	if (crc != je32_to_cpu(ri->data_crc)) {
+		pr_warn("Data CRC %08x != calculated CRC %08x for node at %08x\n",
+			je32_to_cpu(ri->data_crc), crc, ref_offset(fd->raw));
+		ret = -EIO;
+		goto out_decomprbuf;
+	}
+	jffs2_dbg(2, "Data CRC matches calculated CRC %08x\n", crc);
+	if (ri->compr != JFFS2_COMPR_NONE) {
+		jffs2_dbg(2, "Decompress %d bytes from %p to %d bytes at %p\n",
+			  je32_to_cpu(ri->csize), readbuf,
+			  je32_to_cpu(ri->dsize), decomprbuf);
+		ret = jffs2_decompress(c, f, ri->compr | (ri->usercompr << 8), readbuf, decomprbuf, je32_to_cpu(ri->csize), je32_to_cpu(ri->dsize));
+		if (ret) {
+			pr_warn("Error: jffs2_decompress returned %d\n", ret);
+			goto out_decomprbuf;
+		}
+	}
+
+	if (len < je32_to_cpu(ri->dsize)) {
+		memcpy(buf, decomprbuf+ofs, len);
+	}
+ out_decomprbuf:
+	if(decomprbuf != buf && decomprbuf != readbuf)
+		kfree(decomprbuf);
+ out_readbuf:
+	if(readbuf != buf)
+		kfree(readbuf);
+ out_ri:
+	jffs2_free_raw_inode(ri);
+
+	return ret;
+}
+
+int jffs2_read_inode_range(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+			   unsigned char *buf, uint32_t offset, uint32_t len)
+{
+	uint32_t end = offset + len;
+	struct jffs2_node_frag *frag;
+	int ret;
+
+	jffs2_dbg(1, "%s(): ino #%u, range 0x%08x-0x%08x\n",
+		  __func__, f->inocache->ino, offset, offset + len);
+
+	frag = jffs2_lookup_node_frag(&f->fragtree, offset);
+
+	/* XXX FIXME: Where a single physical node actually shows up in two
+	   frags, we read it twice. Don't do that. */
+	/* Now we're pointing at the first frag which overlaps our page
+	 * (or perhaps is before it, if we've been asked to read off the
+	 * end of the file). */
+	while(offset < end) {
+		jffs2_dbg(2, "%s(): offset %d, end %d\n",
+			  __func__, offset, end);
+		if (unlikely(!frag || frag->ofs > offset ||
+			     frag->ofs + frag->size <= offset)) {
+			uint32_t holesize = end - offset;
+			if (frag && frag->ofs > offset) {
+				jffs2_dbg(1, "Eep. Hole in ino #%u fraglist. frag->ofs = 0x%08x, offset = 0x%08x\n",
+					  f->inocache->ino, frag->ofs, offset);
+				holesize = min(holesize, frag->ofs - offset);
+			}
+			jffs2_dbg(1, "Filling non-frag hole from %d-%d\n",
+				  offset, offset + holesize);
+			memset(buf, 0, holesize);
+			buf += holesize;
+			offset += holesize;
+			continue;
+		} else if (unlikely(!frag->node)) {
+			uint32_t holeend = min(end, frag->ofs + frag->size);
+			jffs2_dbg(1, "Filling frag hole from %d-%d (frag 0x%x 0x%x)\n",
+				  offset, holeend, frag->ofs,
+				  frag->ofs + frag->size);
+			memset(buf, 0, holeend - offset);
+			buf += holeend - offset;
+			offset = holeend;
+			frag = frag_next(frag);
+			continue;
+		} else {
+			uint32_t readlen;
+			uint32_t fragofs; /* offset within the frag to start reading */
+
+			fragofs = offset - frag->ofs;
+			readlen = min(frag->size - fragofs, end - offset);
+			jffs2_dbg(1, "Reading %d-%d from node at 0x%08x (%d)\n",
+				  frag->ofs+fragofs,
+				  frag->ofs + fragofs+readlen,
+				  ref_offset(frag->node->raw),
+				  ref_flags(frag->node->raw));
+			ret = jffs2_read_dnode(c, f, frag->node, buf, fragofs + frag->ofs - frag->node->ofs, readlen);
+			jffs2_dbg(2, "node read done\n");
+			if (ret) {
+				jffs2_dbg(1, "%s(): error %d\n",
+					  __func__, ret);
+				memset(buf, 0, readlen);
+				return ret;
+			}
+			buf += readlen;
+			offset += readlen;
+			frag = frag_next(frag);
+			jffs2_dbg(2, "node read was OK. Looping\n");
+		}
+	}
+	return 0;
+}
+