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-nopmd.h | 73 +++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 include/asm-generic/pgtable-nopmd.h (limited to 'include/asm-generic/pgtable-nopmd.h') diff --git a/include/asm-generic/pgtable-nopmd.h b/include/asm-generic/pgtable-nopmd.h new file mode 100644 index 000000000..8ffd64e7a --- /dev/null +++ b/include/asm-generic/pgtable-nopmd.h @@ -0,0 +1,73 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _PGTABLE_NOPMD_H +#define _PGTABLE_NOPMD_H + +#ifndef __ASSEMBLY__ + +#include + +struct mm_struct; + +#define __PAGETABLE_PMD_FOLDED 1 + +/* + * Having the pmd type consist of a pud gets the size right, and allows + * us to conceptually access the pud entry that this pmd is folded into + * without casting. + */ +typedef struct { pud_t pud; } pmd_t; + +#define PMD_SHIFT PUD_SHIFT +#define PTRS_PER_PMD 1 +#define PMD_SIZE (1UL << PMD_SHIFT) +#define PMD_MASK (~(PMD_SIZE-1)) + +/* + * The "pud_xxx()" functions here are trivial for a folded two-level + * setup: the pmd is never bad, and a pmd always exists (as it's folded + * into the pud entry) + */ +static inline int pud_none(pud_t pud) { return 0; } +static inline int pud_bad(pud_t pud) { return 0; } +static inline int pud_present(pud_t pud) { return 1; } +static inline int pud_user(pud_t pud) { return 0; } +static inline int pud_leaf(pud_t pud) { return 0; } +static inline void pud_clear(pud_t *pud) { } +#define pmd_ERROR(pmd) (pud_ERROR((pmd).pud)) + +#define pud_populate(mm, pmd, pte) do { } while (0) + +/* + * (pmds are folded into puds so this doesn't get actually called, + * but the define is needed for a generic inline function.) + */ +#define set_pud(pudptr, pudval) set_pmd((pmd_t *)(pudptr), (pmd_t) { pudval }) + +static inline pmd_t * pmd_offset(pud_t * pud, unsigned long address) +{ + return (pmd_t *)pud; +} +#define pmd_offset pmd_offset + +#define pmd_val(x) (pud_val((x).pud)) +#define __pmd(x) ((pmd_t) { __pud(x) } ) + +#define pud_page(pud) (pmd_page((pmd_t){ pud })) +#define pud_pgtable(pud) ((pmd_t *)(pmd_page_vaddr((pmd_t){ pud }))) + +/* + * allocating and freeing a pmd is trivial: the 1-entry pmd is + * inside the pud, so has no extra memory associated with it. + */ +#define pmd_alloc_one(mm, address) NULL +static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd) +{ +} +#define pmd_free_tlb(tlb, x, a) do { } while (0) + +#undef pmd_addr_end +#define pmd_addr_end(addr, end) (end) + +#endif /* __ASSEMBLY__ */ + +#endif /* _PGTABLE_NOPMD_H */ -- cgit v1.3.1