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, 370 insertions, 0 deletions

diff --git a/scripts/verify_builtin_ranges.awk b/scripts/verify_builtin_ranges.awk
new file mode 100755
index 000000000..0de7ed521
--- /dev/null
+++ b/scripts/verify_builtin_ranges.awk
@@ -0,0 +1,370 @@
+#!/usr/bin/gawk -f
+# SPDX-License-Identifier: GPL-2.0
+# verify_builtin_ranges.awk: Verify address range data for builtin modules
+# Written by Kris Van Hees <kris.van.hees@oracle.com>
+#
+# Usage: verify_builtin_ranges.awk modules.builtin.ranges System.map \
+#				   modules.builtin vmlinux.map vmlinux.o.map
+#
+
+# Return the module name(s) (if any) associated with the given object.
+#
+# If we have seen this object before, return information from the cache.
+# Otherwise, retrieve it from the corresponding .cmd file.
+#
+function get_module_info(fn, mod, obj, s) {
+	if (fn in omod)
+		return omod[fn];
+
+	if (match(fn, /\/[^/]+$/) == 0)
+		return "";
+
+	obj = fn;
+	mod = "";
+	fn = substr(fn, 1, RSTART) "." substr(fn, RSTART + 1) ".cmd";
+	if (getline s <fn == 1) {
+		if (match(s, /DKBUILD_MODFILE=['"]+[^'"]+/) > 0) {
+			mod = substr(s, RSTART + 16, RLENGTH - 16);
+			gsub(/['"]/, "", mod);
+		} else if (match(s, /RUST_MODFILE=[^ ]+/) > 0)
+			mod = substr(s, RSTART + 13, RLENGTH - 13);
+	} else {
+		print "ERROR: Failed to read: " fn "\n\n" \
+		      "  For kernels built with O=<objdir>, cd to <objdir>\n" \
+		      "  and execute this script as ./source/scripts/..." \
+		      >"/dev/stderr";
+		close(fn);
+		total = 0;
+		exit(1);
+	}
+	close(fn);
+
+	# A single module (common case) also reflects objects that are not part
+	# of a module.  Some of those objects have names that are also a module
+	# name (e.g. core).  We check the associated module file name, and if
+	# they do not match, the object is not part of a module.
+	if (mod !~ / /) {
+		if (!(mod in mods))
+			mod = "";
+	}
+
+	gsub(/([^/ ]*\/)+/, "", mod);
+	gsub(/-/, "_", mod);
+
+	# At this point, mod is a single (valid) module name, or a list of
+	# module names (that do not need validation).
+	omod[obj] = mod;
+
+	return mod;
+}
+
+# Return a representative integer value for a given hexadecimal address.
+#
+# Since all kernel addresses fall within the same memory region, we can safely
+# strip off the first 6 hex digits before performing the hex-to-dec conversion,
+# thereby avoiding integer overflows.
+#
+function addr2val(val) {
+	sub(/^0x/, "", val);
+	if (length(val) == 16)
+		val = substr(val, 5);
+	return strtonum("0x" val);
+}
+
+# Determine the kernel build directory to use (default is .).
+#
+BEGIN {
+	if (ARGC < 6) {
+		print "Syntax: verify_builtin_ranges.awk <ranges-file> <system-map>\n" \
+		      "          <builtin-file> <vmlinux-map> <vmlinux-o-map>\n" \
+		      >"/dev/stderr";
+		total = 0;
+		exit(1);
+	}
+}
+
+# (1) Load the built-in module address range data.
+#
+ARGIND == 1 {
+	ranges[FNR] = $0;
+	rcnt++;
+	next;
+}
+
+# (2) Annotate System.map symbols with module names.
+#
+ARGIND == 2 {
+	addr = addr2val($1);
+	name = $3;
+
+	while (addr >= mod_eaddr) {
+		if (sect_symb) {
+			if (sect_symb != name)
+				next;
+
+			sect_base = addr - sect_off;
+			if (dbg)
+				printf "[%s] BASE (%s) %016x - %016x = %016x\n", sect_name, sect_symb, addr, sect_off, sect_base >"/dev/stderr";
+			sect_symb = 0;
+		}
+
+		if (++ridx > rcnt)
+			break;
+
+		$0 = ranges[ridx];
+		sub(/-/, " ");
+		if ($4 != "=") {
+			sub(/-/, " ");
+			mod_saddr = strtonum("0x" $2) + sect_base;
+			mod_eaddr = strtonum("0x" $3) + sect_base;
+			$1 = $2 = $3 = "";
+			sub(/^ +/, "");
+			mod_name = $0;
+
+			if (dbg)
+				printf "[%s] %s from %016x to %016x\n", sect_name, mod_name, mod_saddr, mod_eaddr >"/dev/stderr";
+		} else {
+			sect_name = $1;
+			sect_off = strtonum("0x" $2);
+			sect_symb = $5;
+		}
+	}
+
+	idx = addr"-"name;
+	if (addr >= mod_saddr && addr < mod_eaddr)
+		sym2mod[idx] = mod_name;
+
+	next;
+}
+
+# Once we are done annotating the System.map, we no longer need the ranges data.
+#
+FNR == 1 && ARGIND == 3 {
+	delete ranges;
+}
+
+# (3) Build a lookup map of built-in module names.
+#
+# Lines from modules.builtin will be like:
+#	kernel/crypto/lzo-rle.ko
+# and we record the object name "crypto/lzo-rle".
+#
+ARGIND == 3 {
+	sub(/kernel\//, "");			# strip off "kernel/" prefix
+	sub(/\.ko$/, "");			# strip off .ko suffix
+
+	mods[$1] = 1;
+	next;
+}
+
+# (4) Get a list of symbols (per object).
+#
+# Symbols by object are read from vmlinux.map, with fallback to vmlinux.o.map
+# if vmlinux is found to have inked in vmlinux.o.
+#
+
+# If we were able to get the data we need from vmlinux.map, there is no need to
+# process vmlinux.o.map.
+#
+FNR == 1 && ARGIND == 5 && total > 0 {
+	if (dbg)
+		printf "Note: %s is not needed.\n", FILENAME >"/dev/stderr";
+	exit;
+}
+
+# First determine whether we are dealing with a GNU ld or LLVM lld linker map.
+#
+ARGIND >= 4 && FNR == 1 && NF == 7 && $1 == "VMA" && $7 == "Symbol" {
+	map_is_lld = 1;
+	next;
+}
+
+# (LLD) Convert a section record fronm lld format to ld format.
+#
+ARGIND >= 4 && map_is_lld && NF == 5 && /[0-9] [^ ]+$/ {
+	$0 = $5 " 0x"$1 " 0x"$3 " load address 0x"$2;
+}
+
+# (LLD) Convert an object record from lld format to ld format.
+#
+ARGIND >= 4 && map_is_lld && NF == 5 && $5 ~ /:\(/ {
+	if (/\.a\(/ && !/ vmlinux\.a\(/)
+		next;
+
+	gsub(/\)/, "");
+	sub(/:\(/, " ");
+	sub(/ vmlinux\.a\(/, " ");
+	$0 = " "$6 " 0x"$1 " 0x"$3 " " $5;
+}
+
+# (LLD) Convert a symbol record from lld format to ld format.
+#
+ARGIND >= 4 && map_is_lld && NF == 5 && $5 ~ /^[A-Za-z_][A-Za-z0-9_]*$/ {
+	$0 = "  0x" $1 " " $5;
+}
+
+# (LLD) We do not need any other ldd linker map records.
+#
+ARGIND >= 4 && map_is_lld && /^[0-9a-f]{16} / {
+	next;
+}
+
+# Handle section records with long section names (spilling onto a 2nd line).
+#
+ARGIND >= 4 && !map_is_lld && NF == 1 && /^[^ ]/ {
+	s = $0;
+	getline;
+	$0 = s " " $0;
+}
+
+# Next section - previous one is done.
+#
+ARGIND >= 4 && /^[^ ]/ {
+	sect = 0;
+}
+
+# Get the (top level) section name.
+#
+ARGIND >= 4 && /^\./ {
+	# Explicitly ignore a few sections that are not relevant here.
+	if ($1 ~ /^\.orc_/ || $1 ~ /_sites$/ || $1 ~ /\.percpu/)
+		next;
+
+	# Sections with a 0-address can be ignored as well (in vmlinux.map).
+	if (ARGIND == 4 && $2 ~ /^0x0+$/)
+		next;
+
+	sect = $1;
+
+	next;
+}
+
+# If we are not currently in a section we care about, ignore records.
+#
+!sect {
+	next;
+}
+
+# Handle object records with long section names (spilling onto a 2nd line).
+#
+ARGIND >= 4 && /^ [^ \*]/ && NF == 1 {
+	# If the section name is long, the remainder of the entry is found on
+	# the next line.
+	s = $0;
+	getline;
+	$0 = s " " $0;
+}
+
+# Objects linked in from static libraries are ignored.
+# If the object is vmlinux.o, we need to consult vmlinux.o.map for per-object
+# symbol information
+#
+ARGIND == 4 && /^ [^ ]/ && NF == 4 {
+	if ($4 ~ /\.a\(/)
+		next;
+
+	idx = sect":"$1;
+	if (!(idx in sect_addend)) {
+		sect_addend[idx] = addr2val($2);
+		if (dbg)
+			printf "ADDEND %s = %016x\n", idx, sect_addend[idx] >"/dev/stderr";
+	}
+	if ($4 == "vmlinux.o") {
+		need_o_map = 1;
+		next;
+	}
+}
+
+# If data from vmlinux.o.map is needed, we only process section and object
+# records from vmlinux.map to determine which section we need to pay attention
+# to in vmlinux.o.map.  So skip everything else from vmlinux.map.
+#
+ARGIND == 4 && need_o_map {
+	next;
+}
+
+# Get module information for the current object.
+#
+ARGIND >= 4 && /^ [^ ]/ && NF == 4 {
+	msect = $1;
+	mod_name = get_module_info($4);
+	mod_eaddr = addr2val($2) + addr2val($3);
+
+	next;
+}
+
+# Process a symbol record.
+#
+# Evaluate the module information obtained from vmlinux.map (or vmlinux.o.map)
+# as follows:
+#  - For all symbols in a given object:
+#     - If the symbol is annotated with the same module name(s) that the object
+#       belongs to, count it as a match.
+#     - Otherwise:
+#        - If the symbol is known to have duplicates of which at least one is
+#          in a built-in module, disregard it.
+#        - If the symbol us not annotated with any module name(s) AND the
+#          object belongs to built-in modules, count it as missing.
+#        - Otherwise, count it as a mismatch.
+#
+ARGIND >= 4 && /^ / && NF == 2 && $1 ~ /^0x/ {
+	idx = sect":"msect;
+	if (!(idx in sect_addend))
+		next;
+
+	addr = addr2val($1);
+
+	# Handle the rare but annoying case where a 0-size symbol is placed at
+	# the byte *after* the module range.  Based on vmlinux.map it will be
+	# considered part of the current object, but it falls just beyond the
+	# module address range.  Unfortunately, its address could be at the
+	# start of another built-in module, so the only safe thing to do is to
+	# ignore it.
+	if (mod_name && addr == mod_eaddr)
+		next;
+
+	# If we are processing vmlinux.o.map, we need to apply the base address
+	# of the section to the relative address on the record.
+	#
+	if (ARGIND == 5)
+		addr += sect_addend[idx];
+
+	idx = addr"-"$2;
+	mod = "";
+	if (idx in sym2mod) {
+		mod = sym2mod[idx];
+		if (sym2mod[idx] == mod_name) {
+			mod_matches++;
+			matches++;
+		} else if (mod_name == "") {
+			print $2 " in " mod " (should NOT be)";
+			mismatches++;
+		} else {
+			print $2 " in " mod " (should be " mod_name ")";
+			mismatches++;
+		}
+	} else if (mod_name != "") {
+		print $2 " should be in " mod_name;
+		missing++;
+	} else
+		matches++;
+
+	total++;
+
+	next;
+}
+
+# Issue the comparison report.
+#
+END {
+	if (total) {
+		printf "Verification of %s:\n", ARGV[1];
+		printf "  Correct matches:  %6d (%d%% of total)\n", matches, 100 * matches / total;
+		printf "    Module matches: %6d (%d%% of matches)\n", mod_matches, 100 * mod_matches / matches;
+		printf "  Mismatches:       %6d (%d%% of total)\n", mismatches, 100 * mismatches / total;
+		printf "  Missing:          %6d (%d%% of total)\n", missing, 100 * missing / total;
+
+		if (mismatches || missing)
+			exit(1);
+	}
+}