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 --- samples/kprobes/kprobe_example.c | 129 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+) create mode 100644 samples/kprobes/kprobe_example.c (limited to 'samples/kprobes/kprobe_example.c') diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c new file mode 100644 index 000000000..53ec6c8b8 --- /dev/null +++ b/samples/kprobes/kprobe_example.c @@ -0,0 +1,129 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Here's a sample kernel module showing the use of kprobes to dump a + * stack trace and selected registers when kernel_clone() is called. + * + * For more information on theory of operation of kprobes, see + * Documentation/trace/kprobes.rst + * + * You will see the trace data in /var/log/messages and on the console + * whenever kernel_clone() is invoked to create a new process. + */ + +#define pr_fmt(fmt) "%s: " fmt, __func__ + +#include +#include +#include + +static char symbol[KSYM_NAME_LEN] = "kernel_clone"; +module_param_string(symbol, symbol, KSYM_NAME_LEN, 0644); + +/* For each probe you need to allocate a kprobe structure */ +static struct kprobe kp = { + .symbol_name = symbol, +}; + +/* kprobe pre_handler: called just before the probed instruction is executed */ +static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs) +{ +#ifdef CONFIG_X86 + pr_info("<%s> p->addr = 0x%p, ip = %lx, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->ip, regs->flags); +#endif +#ifdef CONFIG_PPC + pr_info("<%s> p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n", + p->symbol_name, p->addr, regs->nip, regs->msr); +#endif +#ifdef CONFIG_MIPS + pr_info("<%s> p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n", + p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status); +#endif +#ifdef CONFIG_ARM64 + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, pstate = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate); +#endif +#ifdef CONFIG_ARM + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, cpsr = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->ARM_pc, (long)regs->ARM_cpsr); +#endif +#ifdef CONFIG_RISCV + pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, status = 0x%lx\n", + p->symbol_name, p->addr, regs->epc, regs->status); +#endif +#ifdef CONFIG_S390 + pr_info("<%s> p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->psw.addr, regs->flags); +#endif +#ifdef CONFIG_LOONGARCH + pr_info("<%s> p->addr = 0x%p, era = 0x%lx, estat = 0x%lx\n", + p->symbol_name, p->addr, regs->csr_era, regs->csr_estat); +#endif + + /* A dump_stack() here will give a stack backtrace */ + return 0; +} + +/* kprobe post_handler: called after the probed instruction is executed */ +static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs, + unsigned long flags) +{ +#ifdef CONFIG_X86 + pr_info("<%s> p->addr = 0x%p, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->flags); +#endif +#ifdef CONFIG_PPC + pr_info("<%s> p->addr = 0x%p, msr = 0x%lx\n", + p->symbol_name, p->addr, regs->msr); +#endif +#ifdef CONFIG_MIPS + pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n", + p->symbol_name, p->addr, regs->cp0_status); +#endif +#ifdef CONFIG_ARM64 + pr_info("<%s> p->addr = 0x%p, pstate = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->pstate); +#endif +#ifdef CONFIG_ARM + pr_info("<%s> p->addr = 0x%p, cpsr = 0x%lx\n", + p->symbol_name, p->addr, (long)regs->ARM_cpsr); +#endif +#ifdef CONFIG_RISCV + pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n", + p->symbol_name, p->addr, regs->status); +#endif +#ifdef CONFIG_S390 + pr_info("<%s> p->addr, 0x%p, flags = 0x%lx\n", + p->symbol_name, p->addr, regs->flags); +#endif +#ifdef CONFIG_LOONGARCH + pr_info("<%s> p->addr = 0x%p, estat = 0x%lx\n", + p->symbol_name, p->addr, regs->csr_estat); +#endif +} + +static int __init kprobe_init(void) +{ + int ret; + kp.pre_handler = handler_pre; + kp.post_handler = handler_post; + + ret = register_kprobe(&kp); + if (ret < 0) { + pr_err("register_kprobe failed, returned %d\n", ret); + return ret; + } + pr_info("Planted kprobe at %p\n", kp.addr); + return 0; +} + +static void __exit kprobe_exit(void) +{ + unregister_kprobe(&kp); + pr_info("kprobe at %p unregistered\n", kp.addr); +} + +module_init(kprobe_init) +module_exit(kprobe_exit) +MODULE_DESCRIPTION("sample kernel module showing the use of kprobes"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1