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, 94 insertions, 0 deletions

diff --git a/scripts/mksysmap b/scripts/mksysmap
new file mode 100755
index 000000000..c4531eacd
--- /dev/null
+++ b/scripts/mksysmap
@@ -0,0 +1,94 @@
+#!/bin/sed -f
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# sed script to filter out symbols that are not needed for System.map,
+# or not suitable for kallsyms. The input should be 'nm -n <file>'.
+#
+# System.map is used by module-init tools and some debugging
+# tools to retrieve the actual addresses of symbols in the kernel.
+#
+# readprofile starts reading symbols when _stext is found, and
+# continue until it finds a symbol which is not either of 'T', 't',
+# 'W' or 'w'.
+#
+# ---------------------------------------------------------------------------
+# Ignored symbol types
+#
+
+# a: local absolute symbols
+# N: debugging symbols
+# U: undefined global symbols
+# w: local weak symbols
+/ [aNUw] /d
+
+# ---------------------------------------------------------------------------
+# Ignored prefixes
+#  (do not forget a space before each pattern)
+
+# local symbols for ARM, MIPS, etc.
+/ \$/d
+
+# local labels, .LBB, .Ltmpxxx, .L__unnamed_xx, .LASANPC, etc.
+/ \.L/d
+
+# arm64 EFI stub namespace
+/ __efistub_/d
+
+# arm64 local symbols in PIE namespace
+/ __pi_\\$/d
+/ __pi_\.L/d
+
+# arm64 local symbols in non-VHE KVM namespace
+/ __kvm_nvhe_\$/d
+/ __kvm_nvhe_\.L/d
+
+# lld arm/aarch64/mips thunks
+/ __[[:alnum:]]*Thunk_/d
+
+# CFI type identifiers
+/ __kcfi_typeid_/d
+/ __kvm_nvhe___kcfi_typeid_/d
+/ __pi___kcfi_typeid_/d
+
+# CRC from modversions
+/ __crc_/d
+
+# EXPORT_SYMBOL (symbol name)
+/ __kstrtab_/d
+
+# EXPORT_SYMBOL (namespace)
+/ __kstrtabns_/d
+
+# MODULE_DEVICE_TABLE (symbol name)
+/ __mod_device_table__/d
+
+# ---------------------------------------------------------------------------
+# Ignored suffixes
+#  (do not forget '$' after each pattern)
+
+# arm
+/_from_arm$/d
+/_from_thumb$/d
+/_veneer$/d
+
+# ---------------------------------------------------------------------------
+# Ignored symbols (exact match)
+#  (do not forget a space before and '$' after each pattern)
+
+# for LoongArch?
+/ L0$/d
+
+# ppc
+/ _SDA_BASE_$/d
+/ _SDA2_BASE_$/d
+
+# MODULE_INFO()
+/ __UNIQUE_ID_modinfo[0-9]*$/d
+
+# ---------------------------------------------------------------------------
+# Ignored patterns
+#  (symbols that contain the pattern are ignored)
+
+# ppc stub
+/\.long_branch\./d
+/\.plt_branch\./d