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-nopud.h | 66 +++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 include/asm-generic/pgtable-nopud.h (limited to 'include/asm-generic/pgtable-nopud.h') diff --git a/include/asm-generic/pgtable-nopud.h b/include/asm-generic/pgtable-nopud.h new file mode 100644 index 000000000..eb70c6d7c --- /dev/null +++ b/include/asm-generic/pgtable-nopud.h @@ -0,0 +1,66 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _PGTABLE_NOPUD_H +#define _PGTABLE_NOPUD_H + +#ifndef __ASSEMBLY__ + +#include + +#define __PAGETABLE_PUD_FOLDED 1 + +/* + * Having the pud type consist of a p4d gets the size right, and allows + * us to conceptually access the p4d entry that this pud is folded into + * without casting. + */ +typedef struct { p4d_t p4d; } pud_t; + +#define PUD_SHIFT P4D_SHIFT +#define PTRS_PER_PUD 1 +#define PUD_SIZE (1UL << PUD_SHIFT) +#define PUD_MASK (~(PUD_SIZE-1)) + +/* + * The "p4d_xxx()" functions here are trivial for a folded two-level + * setup: the pud is never bad, and a pud always exists (as it's folded + * into the p4d entry) + */ +static inline int p4d_none(p4d_t p4d) { return 0; } +static inline int p4d_bad(p4d_t p4d) { return 0; } +static inline int p4d_present(p4d_t p4d) { return 1; } +static inline void p4d_clear(p4d_t *p4d) { } +#define pud_ERROR(pud) (p4d_ERROR((pud).p4d)) + +#define p4d_populate(mm, p4d, pud) do { } while (0) +#define p4d_populate_safe(mm, p4d, pud) do { } while (0) +/* + * (puds are folded into p4ds so this doesn't get actually called, + * but the define is needed for a generic inline function.) + */ +#define set_p4d(p4dptr, p4dval) set_pud((pud_t *)(p4dptr), (pud_t) { p4dval }) + +static inline pud_t *pud_offset(p4d_t *p4d, unsigned long address) +{ + return (pud_t *)p4d; +} +#define pud_offset pud_offset + +#define pud_val(x) (p4d_val((x).p4d)) +#define __pud(x) ((pud_t) { __p4d(x) }) + +#define p4d_page(p4d) (pud_page((pud_t){ p4d })) +#define p4d_pgtable(p4d) ((pud_t *)(pud_pgtable((pud_t){ p4d }))) + +/* + * allocating and freeing a pud is trivial: the 1-entry pud is + * inside the p4d, so has no extra memory associated with it. + */ +#define pud_alloc_one(mm, address) NULL +#define pud_free(mm, x) do { } while (0) +#define pud_free_tlb(tlb, x, a) do { } while (0) + +#undef pud_addr_end +#define pud_addr_end(addr, end) (end) + +#endif /* __ASSEMBLY__ */ +#endif /* _PGTABLE_NOPUD_H */ -- cgit v1.3.1