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, 426 insertions, 0 deletions

diff --git a/fs/jffs2/compr.c b/fs/jffs2/compr.c
new file mode 100644
index 000000000..764f19dec
--- /dev/null
+++ b/fs/jffs2/compr.c
@@ -0,0 +1,426 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
+ * Copyright © 2004 Ferenc Havasi <havasi@inf.u-szeged.hu>,
+ *		    University of Szeged, Hungary
+ *
+ * Created by Arjan van de Ven <arjan@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "compr.h"
+
+static DEFINE_SPINLOCK(jffs2_compressor_list_lock);
+
+/* Available compressors are on this list */
+static LIST_HEAD(jffs2_compressor_list);
+
+/* Actual compression mode */
+static int jffs2_compression_mode = JFFS2_COMPR_MODE_PRIORITY;
+
+/* Statistics for blocks stored without compression */
+static uint32_t none_stat_compr_blocks=0,none_stat_decompr_blocks=0,none_stat_compr_size=0;
+
+
+/*
+ * Return 1 to use this compression
+ */
+static int jffs2_is_best_compression(struct jffs2_compressor *this,
+		struct jffs2_compressor *best, uint32_t size, uint32_t bestsize)
+{
+	switch (jffs2_compression_mode) {
+	case JFFS2_COMPR_MODE_SIZE:
+		if (bestsize > size)
+			return 1;
+		return 0;
+	case JFFS2_COMPR_MODE_FAVOURLZO:
+		if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > size))
+			return 1;
+		if ((best->compr != JFFS2_COMPR_LZO) && (bestsize > size))
+			return 1;
+		if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > (size * FAVOUR_LZO_PERCENT / 100)))
+			return 1;
+		if ((bestsize * FAVOUR_LZO_PERCENT / 100) > size)
+			return 1;
+
+		return 0;
+	}
+	/* Shouldn't happen */
+	return 0;
+}
+
+/*
+ * jffs2_selected_compress:
+ * @compr: Explicit compression type to use (ie, JFFS2_COMPR_ZLIB).
+ *	If 0, just take the first available compression mode.
+ * @data_in: Pointer to uncompressed data
+ * @cpage_out: Pointer to returned pointer to buffer for compressed data
+ * @datalen: On entry, holds the amount of data available for compression.
+ *	On exit, expected to hold the amount of data actually compressed.
+ * @cdatalen: On entry, holds the amount of space available for compressed
+ *	data. On exit, expected to hold the actual size of the compressed
+ *	data.
+ *
+ * Returns: the compression type used.  Zero is used to show that the data
+ * could not be compressed; probably because we couldn't find the requested
+ * compression mode.
+ */
+static int jffs2_selected_compress(u8 compr, unsigned char *data_in,
+		unsigned char **cpage_out, u32 *datalen, u32 *cdatalen)
+{
+	struct jffs2_compressor *this;
+	int err, ret = JFFS2_COMPR_NONE;
+	uint32_t orig_slen, orig_dlen;
+	char *output_buf;
+
+	output_buf = kmalloc(*cdatalen, GFP_KERNEL);
+	if (!output_buf) {
+		pr_warn("No memory for compressor allocation. Compression failed.\n");
+		return ret;
+	}
+	orig_slen = *datalen;
+	orig_dlen = *cdatalen;
+	spin_lock(&jffs2_compressor_list_lock);
+	list_for_each_entry(this, &jffs2_compressor_list, list) {
+		/* Skip decompress-only and disabled modules */
+		if (!this->compress || this->disabled)
+			continue;
+
+		/* Skip if not the desired compression type */
+		if (compr && (compr != this->compr))
+			continue;
+
+		/*
+		 * Either compression type was unspecified, or we found our
+		 * compressor; either way, we're good to go.
+		 */
+		this->usecount++;
+		spin_unlock(&jffs2_compressor_list_lock);
+
+		*datalen  = orig_slen;
+		*cdatalen = orig_dlen;
+		err = this->compress(data_in, output_buf, datalen, cdatalen);
+
+		spin_lock(&jffs2_compressor_list_lock);
+		this->usecount--;
+		if (!err) {
+			/* Success */
+			ret = this->compr;
+			this->stat_compr_blocks++;
+			this->stat_compr_orig_size += *datalen;
+			this->stat_compr_new_size += *cdatalen;
+			break;
+		}
+	}
+	spin_unlock(&jffs2_compressor_list_lock);
+	if (ret == JFFS2_COMPR_NONE)
+		kfree(output_buf);
+	else
+		*cpage_out = output_buf;
+
+	return ret;
+}
+
+/* jffs2_compress:
+ * @data_in: Pointer to uncompressed data
+ * @cpage_out: Pointer to returned pointer to buffer for compressed data
+ * @datalen: On entry, holds the amount of data available for compression.
+ *	On exit, expected to hold the amount of data actually compressed.
+ * @cdatalen: On entry, holds the amount of space available for compressed
+ *	data. On exit, expected to hold the actual size of the compressed
+ *	data.
+ *
+ * Returns: Lower byte to be stored with data indicating compression type used.
+ * Zero is used to show that the data could not be compressed - the
+ * compressed version was actually larger than the original.
+ * Upper byte will be used later. (soon)
+ *
+ * If the cdata buffer isn't large enough to hold all the uncompressed data,
+ * jffs2_compress should compress as much as will fit, and should set
+ * *datalen accordingly to show the amount of data which were compressed.
+ */
+uint16_t jffs2_compress(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+			unsigned char *data_in, unsigned char **cpage_out,
+			uint32_t *datalen, uint32_t *cdatalen)
+{
+	int ret = JFFS2_COMPR_NONE;
+	int mode, compr_ret;
+	struct jffs2_compressor *this, *best=NULL;
+	unsigned char *output_buf = NULL, *tmp_buf;
+	uint32_t orig_slen, orig_dlen;
+	uint32_t best_slen=0, best_dlen=0;
+
+	if (c->mount_opts.override_compr)
+		mode = c->mount_opts.compr;
+	else
+		mode = jffs2_compression_mode;
+
+	switch (mode) {
+	case JFFS2_COMPR_MODE_NONE:
+		break;
+	case JFFS2_COMPR_MODE_PRIORITY:
+		ret = jffs2_selected_compress(0, data_in, cpage_out, datalen,
+				cdatalen);
+		break;
+	case JFFS2_COMPR_MODE_SIZE:
+	case JFFS2_COMPR_MODE_FAVOURLZO:
+		orig_slen = *datalen;
+		orig_dlen = *cdatalen;
+		spin_lock(&jffs2_compressor_list_lock);
+		list_for_each_entry(this, &jffs2_compressor_list, list) {
+			/* Skip decompress-only backwards-compatibility and disabled modules */
+			if ((!this->compress)||(this->disabled))
+				continue;
+			/* Allocating memory for output buffer if necessary */
+			if ((this->compr_buf_size < orig_slen) && (this->compr_buf)) {
+				spin_unlock(&jffs2_compressor_list_lock);
+				kfree(this->compr_buf);
+				spin_lock(&jffs2_compressor_list_lock);
+				this->compr_buf_size=0;
+				this->compr_buf=NULL;
+			}
+			if (!this->compr_buf) {
+				spin_unlock(&jffs2_compressor_list_lock);
+				tmp_buf = kmalloc(orig_slen, GFP_KERNEL);
+				spin_lock(&jffs2_compressor_list_lock);
+				if (!tmp_buf) {
+					pr_warn("No memory for compressor allocation. (%d bytes)\n",
+						orig_slen);
+					continue;
+				}
+				else {
+					this->compr_buf = tmp_buf;
+					this->compr_buf_size = orig_slen;
+				}
+			}
+			this->usecount++;
+			spin_unlock(&jffs2_compressor_list_lock);
+			*datalen  = orig_slen;
+			*cdatalen = orig_dlen;
+			compr_ret = this->compress(data_in, this->compr_buf, datalen, cdatalen);
+			spin_lock(&jffs2_compressor_list_lock);
+			this->usecount--;
+			if (!compr_ret) {
+				if (((!best_dlen) || jffs2_is_best_compression(this, best, *cdatalen, best_dlen))
+						&& (*cdatalen < *datalen)) {
+					best_dlen = *cdatalen;
+					best_slen = *datalen;
+					best = this;
+				}
+			}
+		}
+		if (best_dlen) {
+			*cdatalen = best_dlen;
+			*datalen  = best_slen;
+			output_buf = best->compr_buf;
+			best->compr_buf = NULL;
+			best->compr_buf_size = 0;
+			best->stat_compr_blocks++;
+			best->stat_compr_orig_size += best_slen;
+			best->stat_compr_new_size  += best_dlen;
+			ret = best->compr;
+			*cpage_out = output_buf;
+		}
+		spin_unlock(&jffs2_compressor_list_lock);
+		break;
+	case JFFS2_COMPR_MODE_FORCELZO:
+		ret = jffs2_selected_compress(JFFS2_COMPR_LZO, data_in,
+				cpage_out, datalen, cdatalen);
+		break;
+	case JFFS2_COMPR_MODE_FORCEZLIB:
+		ret = jffs2_selected_compress(JFFS2_COMPR_ZLIB, data_in,
+				cpage_out, datalen, cdatalen);
+		break;
+	default:
+		pr_err("unknown compression mode\n");
+	}
+
+	if (ret == JFFS2_COMPR_NONE) {
+		*cpage_out = data_in;
+		*datalen = *cdatalen;
+		none_stat_compr_blocks++;
+		none_stat_compr_size += *datalen;
+	}
+	return ret;
+}
+
+int jffs2_decompress(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
+		     uint16_t comprtype, unsigned char *cdata_in,
+		     unsigned char *data_out, uint32_t cdatalen, uint32_t datalen)
+{
+	struct jffs2_compressor *this;
+	int ret;
+
+	/* Older code had a bug where it would write non-zero 'usercompr'
+	   fields. Deal with it. */
+	if ((comprtype & 0xff) <= JFFS2_COMPR_ZLIB)
+		comprtype &= 0xff;
+
+	switch (comprtype & 0xff) {
+	case JFFS2_COMPR_NONE:
+		/* This should be special-cased elsewhere, but we might as well deal with it */
+		memcpy(data_out, cdata_in, datalen);
+		none_stat_decompr_blocks++;
+		break;
+	case JFFS2_COMPR_ZERO:
+		memset(data_out, 0, datalen);
+		break;
+	default:
+		spin_lock(&jffs2_compressor_list_lock);
+		list_for_each_entry(this, &jffs2_compressor_list, list) {
+			if (comprtype == this->compr) {
+				this->usecount++;
+				spin_unlock(&jffs2_compressor_list_lock);
+				ret = this->decompress(cdata_in, data_out, cdatalen, datalen);
+				spin_lock(&jffs2_compressor_list_lock);
+				if (ret) {
+					pr_warn("Decompressor \"%s\" returned %d\n",
+						this->name, ret);
+				}
+				else {
+					this->stat_decompr_blocks++;
+				}
+				this->usecount--;
+				spin_unlock(&jffs2_compressor_list_lock);
+				return ret;
+			}
+		}
+		pr_warn("compression type 0x%02x not available\n", comprtype);
+		spin_unlock(&jffs2_compressor_list_lock);
+		return -EIO;
+	}
+	return 0;
+}
+
+int jffs2_register_compressor(struct jffs2_compressor *comp)
+{
+	struct jffs2_compressor *this;
+
+	if (!comp->name) {
+		pr_warn("NULL compressor name at registering JFFS2 compressor. Failed.\n");
+		return -1;
+	}
+	comp->compr_buf_size=0;
+	comp->compr_buf=NULL;
+	comp->usecount=0;
+	comp->stat_compr_orig_size=0;
+	comp->stat_compr_new_size=0;
+	comp->stat_compr_blocks=0;
+	comp->stat_decompr_blocks=0;
+	jffs2_dbg(1, "Registering JFFS2 compressor \"%s\"\n", comp->name);
+
+	spin_lock(&jffs2_compressor_list_lock);
+
+	list_for_each_entry(this, &jffs2_compressor_list, list) {
+		if (this->priority < comp->priority) {
+			list_add(&comp->list, this->list.prev);
+			goto out;
+		}
+	}
+	list_add_tail(&comp->list, &jffs2_compressor_list);
+out:
+	D2(list_for_each_entry(this, &jffs2_compressor_list, list) {
+		printk(KERN_DEBUG "Compressor \"%s\", prio %d\n", this->name, this->priority);
+	})
+
+	spin_unlock(&jffs2_compressor_list_lock);
+
+	return 0;
+}
+
+int jffs2_unregister_compressor(struct jffs2_compressor *comp)
+{
+	D2(struct jffs2_compressor *this);
+
+	jffs2_dbg(1, "Unregistering JFFS2 compressor \"%s\"\n", comp->name);
+
+	spin_lock(&jffs2_compressor_list_lock);
+
+	if (comp->usecount) {
+		spin_unlock(&jffs2_compressor_list_lock);
+		pr_warn("Compressor module is in use. Unregister failed.\n");
+		return -1;
+	}
+	list_del(&comp->list);
+
+	D2(list_for_each_entry(this, &jffs2_compressor_list, list) {
+		printk(KERN_DEBUG "Compressor \"%s\", prio %d\n", this->name, this->priority);
+	})
+	spin_unlock(&jffs2_compressor_list_lock);
+	return 0;
+}
+
+void jffs2_free_comprbuf(unsigned char *comprbuf, unsigned char *orig)
+{
+	if (orig != comprbuf)
+		kfree(comprbuf);
+}
+
+int __init jffs2_compressors_init(void)
+{
+	int ret = 0;
+/* Registering compressors */
+	ret = jffs2_zlib_init();
+	if (ret)
+		goto exit;
+	ret = jffs2_rtime_init();
+	if (ret)
+		goto exit_zlib;
+	ret = jffs2_rubinmips_init();
+	if (ret)
+		goto exit_rtime;
+	ret = jffs2_dynrubin_init();
+	if (ret)
+		goto exit_runinmips;
+	ret = jffs2_lzo_init();
+	if (ret)
+		goto exit_dynrubin;
+
+
+/* Setting default compression mode */
+#ifdef CONFIG_JFFS2_CMODE_NONE
+	jffs2_compression_mode = JFFS2_COMPR_MODE_NONE;
+	jffs2_dbg(1, "default compression mode: none\n");
+#else
+#ifdef CONFIG_JFFS2_CMODE_SIZE
+	jffs2_compression_mode = JFFS2_COMPR_MODE_SIZE;
+	jffs2_dbg(1, "default compression mode: size\n");
+#else
+#ifdef CONFIG_JFFS2_CMODE_FAVOURLZO
+	jffs2_compression_mode = JFFS2_COMPR_MODE_FAVOURLZO;
+	jffs2_dbg(1, "default compression mode: favourlzo\n");
+#else
+	jffs2_dbg(1, "default compression mode: priority\n");
+#endif
+#endif
+#endif
+	return 0;
+
+exit_dynrubin:
+	jffs2_dynrubin_exit();
+exit_runinmips:
+	jffs2_rubinmips_exit();
+exit_rtime:
+	jffs2_rtime_exit();
+exit_zlib:
+	jffs2_zlib_exit();
+exit:
+	return ret;
+}
+
+int jffs2_compressors_exit(void)
+{
+/* Unregistering compressors */
+	jffs2_lzo_exit();
+	jffs2_dynrubin_exit();
+	jffs2_rubinmips_exit();
+	jffs2_rtime_exit();
+	jffs2_zlib_exit();
+	return 0;
+}