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, 222 insertions, 0 deletions

diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
new file mode 100644
index 000000000..5698dae5d
--- /dev/null
+++ b/fs/jffs2/compr_zlib.c
@@ -0,0 +1,222 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#if !defined(__KERNEL__) && !defined(__ECOS)
+#error "The userspace support got too messy and was removed. Update your mkfs.jffs2"
+#endif
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/zlib.h>
+#include <linux/zutil.h>
+#include "nodelist.h"
+#include "compr.h"
+
+	/* Plan: call deflate() with avail_in == *sourcelen,
+		avail_out = *dstlen - 12 and flush == Z_FINISH.
+		If it doesn't manage to finish,	call it again with
+		avail_in == 0 and avail_out set to the remaining 12
+		bytes for it to clean up.
+	   Q: Is 12 bytes sufficient?
+	*/
+#define STREAM_END_SPACE 12
+
+static DEFINE_MUTEX(deflate_mutex);
+static DEFINE_MUTEX(inflate_mutex);
+static z_stream inf_strm, def_strm;
+
+#ifdef __KERNEL__ /* Linux-only */
+#include <linux/vmalloc.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+
+static int __init alloc_workspaces(void)
+{
+	def_strm.workspace = vmalloc(zlib_deflate_workspacesize(MAX_WBITS,
+							MAX_MEM_LEVEL));
+	if (!def_strm.workspace)
+		return -ENOMEM;
+
+	jffs2_dbg(1, "Allocated %d bytes for deflate workspace\n",
+		  zlib_deflate_workspacesize(MAX_WBITS, MAX_MEM_LEVEL));
+	inf_strm.workspace = vmalloc(zlib_inflate_workspacesize());
+	if (!inf_strm.workspace) {
+		vfree(def_strm.workspace);
+		return -ENOMEM;
+	}
+	jffs2_dbg(1, "Allocated %d bytes for inflate workspace\n",
+		  zlib_inflate_workspacesize());
+	return 0;
+}
+
+static void free_workspaces(void)
+{
+	vfree(def_strm.workspace);
+	vfree(inf_strm.workspace);
+}
+#else
+#define alloc_workspaces() (0)
+#define free_workspaces() do { } while(0)
+#endif /* __KERNEL__ */
+
+static int jffs2_zlib_compress(unsigned char *data_in,
+			       unsigned char *cpage_out,
+			       uint32_t *sourcelen, uint32_t *dstlen)
+{
+	int ret;
+
+	if (*dstlen <= STREAM_END_SPACE)
+		return -1;
+
+	mutex_lock(&deflate_mutex);
+
+	if (Z_OK != zlib_deflateInit(&def_strm, 3)) {
+		pr_warn("deflateInit failed\n");
+		mutex_unlock(&deflate_mutex);
+		return -1;
+	}
+
+	def_strm.next_in = data_in;
+	def_strm.total_in = 0;
+
+	def_strm.next_out = cpage_out;
+	def_strm.total_out = 0;
+
+	while (def_strm.total_out < *dstlen - STREAM_END_SPACE && def_strm.total_in < *sourcelen) {
+		def_strm.avail_out = *dstlen - (def_strm.total_out + STREAM_END_SPACE);
+		def_strm.avail_in = min_t(unsigned long,
+			(*sourcelen-def_strm.total_in), def_strm.avail_out);
+		jffs2_dbg(1, "calling deflate with avail_in %ld, avail_out %ld\n",
+			  def_strm.avail_in, def_strm.avail_out);
+		ret = zlib_deflate(&def_strm, Z_PARTIAL_FLUSH);
+		jffs2_dbg(1, "deflate returned with avail_in %ld, avail_out %ld, total_in %ld, total_out %ld\n",
+			  def_strm.avail_in, def_strm.avail_out,
+			  def_strm.total_in, def_strm.total_out);
+		if (ret != Z_OK) {
+			jffs2_dbg(1, "deflate in loop returned %d\n", ret);
+			zlib_deflateEnd(&def_strm);
+			mutex_unlock(&deflate_mutex);
+			return -1;
+		}
+	}
+	def_strm.avail_out += STREAM_END_SPACE;
+	def_strm.avail_in = 0;
+	ret = zlib_deflate(&def_strm, Z_FINISH);
+	zlib_deflateEnd(&def_strm);
+
+	if (ret != Z_STREAM_END) {
+		jffs2_dbg(1, "final deflate returned %d\n", ret);
+		ret = -1;
+		goto out;
+	}
+
+	if (def_strm.total_out >= def_strm.total_in) {
+		jffs2_dbg(1, "zlib compressed %ld bytes into %ld; failing\n",
+			  def_strm.total_in, def_strm.total_out);
+		ret = -1;
+		goto out;
+	}
+
+	jffs2_dbg(1, "zlib compressed %ld bytes into %ld\n",
+		  def_strm.total_in, def_strm.total_out);
+
+	*dstlen = def_strm.total_out;
+	*sourcelen = def_strm.total_in;
+	ret = 0;
+ out:
+	mutex_unlock(&deflate_mutex);
+	return ret;
+}
+
+static int jffs2_zlib_decompress(unsigned char *data_in,
+				 unsigned char *cpage_out,
+				 uint32_t srclen, uint32_t destlen)
+{
+	int ret;
+	int wbits = MAX_WBITS;
+
+	mutex_lock(&inflate_mutex);
+
+	inf_strm.next_in = data_in;
+	inf_strm.avail_in = srclen;
+	inf_strm.total_in = 0;
+
+	inf_strm.next_out = cpage_out;
+	inf_strm.avail_out = destlen;
+	inf_strm.total_out = 0;
+
+	/* If it's deflate, and it's got no preset dictionary, then
+	   we can tell zlib to skip the adler32 check. */
+	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
+	    ((data_in[0] & 0x0f) == Z_DEFLATED) &&
+	    !(((data_in[0]<<8) + data_in[1]) % 31)) {
+
+		jffs2_dbg(2, "inflate skipping adler32\n");
+		wbits = -((data_in[0] >> 4) + 8);
+		inf_strm.next_in += 2;
+		inf_strm.avail_in -= 2;
+	} else {
+		/* Let this remain D1 for now -- it should never happen */
+		jffs2_dbg(1, "inflate not skipping adler32\n");
+	}
+
+
+	if (Z_OK != zlib_inflateInit2(&inf_strm, wbits)) {
+		pr_warn("inflateInit failed\n");
+		mutex_unlock(&inflate_mutex);
+		return 1;
+	}
+
+	while((ret = zlib_inflate(&inf_strm, Z_FINISH)) == Z_OK)
+		;
+	if (ret != Z_STREAM_END) {
+		pr_notice("inflate returned %d\n", ret);
+	}
+	zlib_inflateEnd(&inf_strm);
+	mutex_unlock(&inflate_mutex);
+	return 0;
+}
+
+static struct jffs2_compressor jffs2_zlib_comp = {
+    .priority = JFFS2_ZLIB_PRIORITY,
+    .name = "zlib",
+    .compr = JFFS2_COMPR_ZLIB,
+    .compress = &jffs2_zlib_compress,
+    .decompress = &jffs2_zlib_decompress,
+#ifdef JFFS2_ZLIB_DISABLED
+    .disabled = 1,
+#else
+    .disabled = 0,
+#endif
+};
+
+int __init jffs2_zlib_init(void)
+{
+    int ret;
+
+    ret = alloc_workspaces();
+    if (ret)
+	    return ret;
+
+    ret = jffs2_register_compressor(&jffs2_zlib_comp);
+    if (ret)
+	    free_workspaces();
+
+    return ret;
+}
+
+void jffs2_zlib_exit(void)
+{
+    jffs2_unregister_compressor(&jffs2_zlib_comp);
+    free_workspaces();
+}