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, 411 insertions, 0 deletions

diff --git a/arch/arm64/tools/gen-sysreg.awk b/arch/arm64/tools/gen-sysreg.awk
new file mode 100755
index 000000000..86860ab67
--- /dev/null
+++ b/arch/arm64/tools/gen-sysreg.awk
@@ -0,0 +1,411 @@
+#!/bin/awk -f
+# SPDX-License-Identifier: GPL-2.0
+# gen-sysreg.awk: arm64 sysreg header generator
+#
+# Usage: awk -f gen-sysreg.awk sysregs.txt
+
+function block_current() {
+	return __current_block[__current_block_depth];
+}
+
+# Log an error and terminate
+function fatal(msg) {
+	print "Error at " NR ": " msg > "/dev/stderr"
+
+	printf "Current block nesting:"
+
+	for (i = 0; i <= __current_block_depth; i++) {
+		printf " " __current_block[i]
+	}
+	printf "\n"
+
+	exit 1
+}
+
+# Enter a new block, setting the active block to @block
+function block_push(block) {
+	__current_block[++__current_block_depth] = block
+}
+
+# Exit a block, setting the active block to the parent block
+function block_pop() {
+	if (__current_block_depth == 0)
+		fatal("error: block_pop() in root block")
+
+	__current_block_depth--;
+}
+
+# Sanity check the number of records for a field makes sense. If not, produce
+# an error and terminate.
+function expect_fields(nf) {
+	if (NF != nf)
+		fatal(NF " fields found where " nf " expected")
+}
+
+# Print a CPP macro definition, padded with spaces so that the macro bodies
+# line up in a column
+function define(prefix, name, val) {
+	printf "%-56s%s\n", "#define " prefix name, val
+}
+
+# Same as above, but without a prefix
+function define_reg(name, val) {
+	define(null, name, val)
+}
+
+# Print standard BITMASK/SHIFT/WIDTH CPP definitions for a field
+function define_field(prefix, reg, field, msb, lsb) {
+	define(prefix, reg "_" field, "GENMASK(" msb ", " lsb ")")
+	define(prefix, reg "_" field "_MASK", "GENMASK(" msb ", " lsb ")")
+	define(prefix, reg "_" field "_SHIFT", lsb)
+	define(prefix, reg "_" field "_WIDTH", msb - lsb + 1)
+}
+
+# Print a field _SIGNED definition for a field
+function define_field_sign(prefix, reg, field, sign) {
+	define(prefix, reg "_" field "_SIGNED", sign)
+}
+
+# Print the Res0, Res1, Unkn masks
+function define_resx_unkn(prefix, reg, res0, res1, unkn) {
+	if (res0 != null)
+		define(prefix, reg "_RES0", "(" res0 ")")
+	if (res1 != null)
+		define(prefix, reg "_RES1", "(" res1 ")")
+	if (unkn != null)
+		define(prefix, reg "_UNKN", "(" unkn ")")
+	if (res0 != null || res1 != null || unkn != null)
+		print ""
+}
+
+# Parse a "<msb>[:<lsb>]" string into the global variables @msb and @lsb
+function parse_bitdef(reg, field, bitdef, _bits)
+{
+	if (bitdef ~ /^[0-9]+$/) {
+		msb = bitdef
+		lsb = bitdef
+	} else if (split(bitdef, _bits, ":") == 2) {
+		msb = _bits[1]
+		lsb = _bits[2]
+	} else {
+		fatal("invalid bit-range definition '" bitdef "'")
+	}
+
+
+	if (msb != next_bit)
+		fatal(reg "." field " starts at " msb " not " next_bit)
+	if (63 < msb || msb < 0)
+		fatal(reg "." field " invalid high bit in '" bitdef "'")
+	if (63 < lsb || lsb < 0)
+		fatal(reg "." field " invalid low bit in '" bitdef "'")
+	if (msb < lsb)
+		fatal(reg "." field " invalid bit-range '" bitdef "'")
+	if (low > high)
+		fatal(reg "." field " has invalid range " high "-" low)
+
+	next_bit = lsb - 1
+}
+
+BEGIN {
+	print "#ifndef __ASM_SYSREG_DEFS_H"
+	print "#define __ASM_SYSREG_DEFS_H"
+	print ""
+	print "/* Generated file - do not edit */"
+	print ""
+
+	__current_block_depth = 0
+	__current_block[__current_block_depth] = "Root"
+}
+
+END {
+	if (__current_block_depth != 0)
+		fatal("Missing terminator for " block_current() " block")
+
+	print "#endif /* __ASM_SYSREG_DEFS_H */"
+}
+
+# skip blank lines and comment lines
+/^$/ { next }
+/^[\t ]*#/ { next }
+
+$1 == "SysregFields" && block_current() == "Root" {
+	block_push("SysregFields")
+
+	expect_fields(2)
+
+	reg = $2
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+
+	if (reg in defined_fields)
+		fatal("Duplicate SysregFields definition for " reg)
+	defined_fields[reg] = 1
+
+	next_bit = 63
+
+	delete seen_prefixes
+
+	next
+}
+
+$1 == "EndSysregFields" && block_current() == "SysregFields" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	reg = null
+	res0 = null
+	res1 = null
+	unkn = null
+
+	block_pop()
+	next
+}
+
+$1 == "Sysreg" && block_current() == "Root" {
+	block_push("Sysreg")
+
+	expect_fields(7)
+
+	reg = $2
+	op0 = $3
+	op1 = $4
+	crn = $5
+	crm = $6
+	op2 = $7
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+
+	if (reg in defined_regs)
+		fatal("Duplicate Sysreg definition for " reg)
+	defined_regs[reg] = 1
+
+	define_reg("REG_" reg, "S" op0 "_" op1 "_C" crn "_C" crm "_" op2)
+	define_reg("SYS_" reg, "sys_reg(" op0 ", " op1 ", " crn ", " crm ", " op2 ")")
+
+	define_reg("SYS_" reg "_Op0", op0)
+	define_reg("SYS_" reg "_Op1", op1)
+	define_reg("SYS_" reg "_CRn", crn)
+	define_reg("SYS_" reg "_CRm", crm)
+	define_reg("SYS_" reg "_Op2", op2)
+
+	print ""
+
+	prefix = null
+	next_bit = 63
+
+	delete seen_prefixes
+
+	next
+}
+
+$1 == "EndSysreg" && block_current() == "Sysreg" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	reg = null
+	op0 = null
+	op1 = null
+	crn = null
+	crm = null
+	op2 = null
+	res0 = null
+	res1 = null
+	unkn = null
+	prefix = null
+
+	block_pop()
+	next
+}
+
+# Currently this is effectivey a comment, in future we may want to emit
+# defines for the fields.
+($1 == "Fields" || $1 == "Mapping") && block_current() == "Sysreg" {
+	expect_fields(2)
+
+	if (next_bit != 63)
+		fatal("Some fields already defined for " reg)
+
+	print "/* For " reg " fields see " $2 " */"
+	print ""
+
+	next_bit = -1
+	res0 = null
+	res1 = null
+	unkn = null
+
+	next
+}
+
+$1 == "Res0" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "RES0", $2)
+	field = "RES0_" msb "_" lsb
+
+	res0 = res0 " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Res1" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "RES1", $2)
+	field = "RES1_" msb "_" lsb
+
+	res1 = res1 " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Unkn" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "UNKN", $2)
+	field = "UNKN_" msb "_" lsb
+
+	unkn = unkn " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Field" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	print ""
+
+	next
+}
+
+$1 == "Raz" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, field, $2)
+
+	next
+}
+
+$1 == "SignedEnum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	define_field_sign(prefix, reg, field, "true")
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "UnsignedEnum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	define_field_sign(prefix, reg, field, "false")
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "Enum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "EndEnum" && block_current() == "Enum" {
+	expect_fields(1)
+
+	field = null
+	msb = null
+	lsb = null
+	print ""
+
+	delete seen_enum_vals
+
+	block_pop()
+	next
+}
+
+/0b[01]+/ && block_current() == "Enum" {
+	expect_fields(2)
+	val = $1
+	name = $2
+
+	if (val in seen_enum_vals)
+		fatal("Duplicate Enum value " val " for " name)
+	seen_enum_vals[val] = 1
+
+	define(prefix, reg "_" field "_" name, "UL(" val ")")
+	next
+}
+
+$1 == "Prefix" && (block_current() == "Sysreg" || block_current() == "SysregFields") {
+	block_push("Prefix")
+
+	expect_fields(2)
+
+	if (next_bit < 63)
+		fatal("Prefixed fields must precede non-prefixed fields (" reg ")")
+
+	prefix = $2 "_"
+
+	if (prefix in seen_prefixes)
+		fatal("Duplicate prefix " prefix " for " reg)
+	seen_prefixes[prefix] = 1
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+	next_bit = 63
+
+	next
+}
+
+$1 == "EndPrefix" && block_current() == "Prefix" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in prefix " prefix " for " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	prefix = null
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+	next_bit = 63
+
+	block_pop()
+
+	next
+}
+
+# Any lines not handled by previous rules are unexpected
+{
+	fatal("unhandled statement")
+}