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/cmpxchg.h | 115 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) create mode 100644 include/asm-generic/cmpxchg.h (limited to 'include/asm-generic/cmpxchg.h') diff --git a/include/asm-generic/cmpxchg.h b/include/asm-generic/cmpxchg.h new file mode 100644 index 000000000..848de25fc --- /dev/null +++ b/include/asm-generic/cmpxchg.h @@ -0,0 +1,115 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Generic UP xchg and cmpxchg using interrupt disablement. Does not + * support SMP. + */ + +#ifndef __ASM_GENERIC_CMPXCHG_H +#define __ASM_GENERIC_CMPXCHG_H + +#ifdef CONFIG_SMP +#error "Cannot use generic cmpxchg on SMP" +#endif + +#include +#include + +/* + * This function doesn't exist, so you'll get a linker error if + * something tries to do an invalidly-sized xchg(). + */ +extern void __generic_xchg_called_with_bad_pointer(void); + +static inline +unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size) +{ + unsigned long ret, flags; + + switch (size) { + case 1: +#ifdef __xchg_u8 + return __xchg_u8(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u8 *)ptr; + *(volatile u8 *)ptr = (x & 0xffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u8 */ + + case 2: +#ifdef __xchg_u16 + return __xchg_u16(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u16 *)ptr; + *(volatile u16 *)ptr = (x & 0xffffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u16 */ + + case 4: +#ifdef __xchg_u32 + return __xchg_u32(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u32 *)ptr; + *(volatile u32 *)ptr = (x & 0xffffffffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u32 */ + +#ifdef CONFIG_64BIT + case 8: +#ifdef __xchg_u64 + return __xchg_u64(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u64 *)ptr; + *(volatile u64 *)ptr = x; + local_irq_restore(flags); + return ret; +#endif /* __xchg_u64 */ +#endif /* CONFIG_64BIT */ + + default: + __generic_xchg_called_with_bad_pointer(); + return x; + } +} + +#define generic_xchg(ptr, x) ({ \ + ((__typeof__(*(ptr))) \ + __generic_xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))); \ +}) + +/* + * Atomic compare and exchange. + */ +#include + +#define generic_cmpxchg_local(ptr, o, n) ({ \ + ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o), \ + (unsigned long)(n), sizeof(*(ptr)))); \ +}) + +#define generic_cmpxchg64_local(ptr, o, n) \ + __generic_cmpxchg64_local((ptr), (o), (n)) + + +#ifndef arch_xchg +#define arch_xchg generic_xchg +#endif + +#ifndef arch_cmpxchg_local +#define arch_cmpxchg_local generic_cmpxchg_local +#endif + +#ifndef arch_cmpxchg64_local +#define arch_cmpxchg64_local generic_cmpxchg64_local +#endif + +#define arch_cmpxchg arch_cmpxchg_local +#define arch_cmpxchg64 arch_cmpxchg64_local + +#endif /* __ASM_GENERIC_CMPXCHG_H */ -- cgit v1.3.1