| 1 | /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only) |
| 2 | * |
| 3 | * wrapper/kallsyms.c |
| 4 | * |
| 5 | * Wrapper around kallsyms. Using kprobes to get its address when available. |
| 6 | * |
| 7 | * Can we mainline LTTng already so we don't have to waste our time doing this |
| 8 | * kind of hack ? |
| 9 | * |
| 10 | * Copyright (C) 2020 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 11 | */ |
| 12 | |
| 13 | #include <linux/kprobes.h> |
| 14 | #include <linux/module.h> |
| 15 | #include <wrapper/kallsyms.h> |
| 16 | |
| 17 | #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,7,0)) |
| 18 | |
| 19 | #ifndef CONFIG_KPROBES |
| 20 | # error "LTTng-modules requires CONFIG_KPROBES on kernels >= 5.7.0" |
| 21 | #endif |
| 22 | |
| 23 | static |
| 24 | unsigned long (*kallsyms_lookup_name_sym)(const char *name); |
| 25 | |
| 26 | static |
| 27 | int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs) |
| 28 | { |
| 29 | return 0; |
| 30 | } |
| 31 | |
| 32 | static |
| 33 | unsigned long do_get_kallsyms(void) |
| 34 | { |
| 35 | struct kprobe probe; |
| 36 | int ret; |
| 37 | unsigned long addr; |
| 38 | |
| 39 | memset(&probe, 0, sizeof(probe)); |
| 40 | probe.pre_handler = dummy_kprobe_handler; |
| 41 | probe.symbol_name = "kallsyms_lookup_name"; |
| 42 | #ifdef LTTNG_CONFIG_PPC64_ELF_ABI_V2 |
| 43 | /* |
| 44 | * With powerpc64 ABIv2, we need the global entry point of |
| 45 | * kallsyms_lookup_name to call it later, while kprobe_register would |
| 46 | * automatically adjust the global entry point to the local entry point, |
| 47 | * when a kprobe was registered at a function entry. So we add 4 bytes |
| 48 | * which is the length of one instruction to kallsyms_lookup_name to |
| 49 | * avoid the adjustment. |
| 50 | */ |
| 51 | probe.offset = 4; |
| 52 | #endif |
| 53 | ret = register_kprobe(&probe); |
| 54 | if (ret) |
| 55 | return 0; |
| 56 | #ifdef LTTNG_CONFIG_PPC64_ELF_ABI_V2 |
| 57 | /* Substract 4 bytes to get what we originally want */ |
| 58 | addr = (unsigned long)(((char *)probe.addr) - 4); |
| 59 | #else |
| 60 | addr = (unsigned long)probe.addr; |
| 61 | #endif |
| 62 | #ifdef CONFIG_ARM |
| 63 | #ifdef CONFIG_THUMB2_KERNEL |
| 64 | if (addr) |
| 65 | addr |= 1; /* set bit 0 in address for thumb mode */ |
| 66 | #endif |
| 67 | #endif |
| 68 | unregister_kprobe(&probe); |
| 69 | return addr; |
| 70 | } |
| 71 | |
| 72 | unsigned long wrapper_kallsyms_lookup_name(const char *name) |
| 73 | { |
| 74 | if (!kallsyms_lookup_name_sym) { |
| 75 | kallsyms_lookup_name_sym = (void *)do_get_kallsyms(); |
| 76 | } |
| 77 | if (kallsyms_lookup_name_sym) |
| 78 | return kallsyms_lookup_name_sym(name); |
| 79 | else { |
| 80 | printk_once(KERN_WARNING "LTTng: requires kallsyms_lookup_name\n"); |
| 81 | return 0; |
| 82 | } |
| 83 | } |
| 84 | EXPORT_SYMBOL_GPL(wrapper_kallsyms_lookup_name); |
| 85 | |
| 86 | #endif |