From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers 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 Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- include/asm-generic/pgtable-nop4d.h | 58 +++++++++++++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) create mode 100644 include/asm-generic/pgtable-nop4d.h (limited to 'include/asm-generic/pgtable-nop4d.h') diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h new file mode 100644 index 000000000..03b7dae47 --- /dev/null +++ b/include/asm-generic/pgtable-nop4d.h @@ -0,0 +1,58 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _PGTABLE_NOP4D_H +#define _PGTABLE_NOP4D_H + +#ifndef __ASSEMBLY__ + +#define __PAGETABLE_P4D_FOLDED 1 + +typedef struct { pgd_t pgd; } p4d_t; + +#define P4D_SHIFT PGDIR_SHIFT +#define PTRS_PER_P4D 1 +#define P4D_SIZE (1UL << P4D_SHIFT) +#define P4D_MASK (~(P4D_SIZE-1)) + +/* + * The "pgd_xxx()" functions here are trivial for a folded two-level + * setup: the p4d is never bad, and a p4d always exists (as it's folded + * into the pgd entry) + */ +static inline int pgd_none(pgd_t pgd) { return 0; } +static inline int pgd_bad(pgd_t pgd) { return 0; } +static inline int pgd_present(pgd_t pgd) { return 1; } +static inline void pgd_clear(pgd_t *pgd) { } +#define p4d_ERROR(p4d) (pgd_ERROR((p4d).pgd)) + +#define pgd_populate(mm, pgd, p4d) do { } while (0) +#define pgd_populate_safe(mm, pgd, p4d) do { } while (0) +/* + * (p4ds are folded into pgds so this doesn't get actually called, + * but the define is needed for a generic inline function.) + */ +#define set_pgd(pgdptr, pgdval) set_p4d((p4d_t *)(pgdptr), (p4d_t) { pgdval }) + +static inline p4d_t *p4d_offset(pgd_t *pgd, unsigned long address) +{ + return (p4d_t *)pgd; +} + +#define p4d_val(x) (pgd_val((x).pgd)) +#define __p4d(x) ((p4d_t) { __pgd(x) }) + +#define pgd_page(pgd) (p4d_page((p4d_t){ pgd })) +#define pgd_page_vaddr(pgd) ((unsigned long)(p4d_pgtable((p4d_t){ pgd }))) + +/* + * allocating and freeing a p4d is trivial: the 1-entry p4d is + * inside the pgd, so has no extra memory associated with it. + */ +#define p4d_alloc_one(mm, address) NULL +#define p4d_free(mm, x) do { } while (0) +#define p4d_free_tlb(tlb, x, a) do { } while (0) + +#undef p4d_addr_end +#define p4d_addr_end(addr, end) (end) + +#endif /* __ASSEMBLY__ */ +#endif /* _PGTABLE_NOP4D_H */ -- cgit v1.3.1