1 // SPDX-License-Identifier: GPL-2.0-only
3 * Here's a sample kernel module showing the use of fprobe to dump a
4 * stack trace and selected registers when kernel_clone() is called.
6 * For more information on theory of operation of kprobes, see
7 * Documentation/trace/kprobes.rst
9 * You will see the trace data in /var/log/messages and on the console
10 * whenever kernel_clone() is invoked to create a new process.
13 #define pr_fmt(fmt) "%s: " fmt, __func__
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/fprobe.h>
18 #include <linux/sched/debug.h>
19 #include <linux/slab.h>
21 #define BACKTRACE_DEPTH 16
22 #define MAX_SYMBOL_LEN 4096
23 static struct fprobe sample_probe;
24 static unsigned long nhit;
26 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
27 module_param_string(symbol, symbol, sizeof(symbol), 0644);
28 MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern.");
30 static char nosymbol[MAX_SYMBOL_LEN] = "";
31 module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
32 MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern.");
34 static bool stackdump = true;
35 module_param(stackdump, bool, 0644);
36 MODULE_PARM_DESC(stackdump, "Enable stackdump.");
38 static bool use_trace = false;
39 module_param(use_trace, bool, 0644);
40 MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging.");
42 static void show_backtrace(void)
44 unsigned long stacks[BACKTRACE_DEPTH];
47 len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
48 stack_trace_print(stacks, len, 24);
51 static void sample_entry_handler(struct fprobe *fp, unsigned long ip,
52 struct pt_regs *regs, void *data)
56 * This is just an example, no kernel code should call
57 * trace_printk() except when actively debugging.
59 trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
61 pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
67 static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs,
70 unsigned long rip = instruction_pointer(regs);
74 * This is just an example, no kernel code should call
75 * trace_printk() except when actively debugging.
77 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
78 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
80 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
81 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
87 static int __init fprobe_init(void)
89 char *p, *symbuf = NULL;
93 sample_probe.entry_handler = sample_entry_handler;
94 sample_probe.exit_handler = sample_exit_handler;
96 if (strchr(symbol, '*')) {
97 /* filter based fprobe */
98 ret = register_fprobe(&sample_probe, symbol,
99 nosymbol[0] == '\0' ? NULL : nosymbol);
101 } else if (!strchr(symbol, ',')) {
103 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
107 /* Comma separated symbols */
108 symbuf = kstrdup(symbol, GFP_KERNEL);
113 while ((p = strchr(++p, ',')) != NULL)
116 pr_info("%d symbols found\n", count);
118 syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
125 for (i = 0; i < count; i++)
126 syms[i] = strsep(&p, ",");
128 ret = register_fprobe_syms(&sample_probe, syms, count);
133 pr_err("register_fprobe failed, returned %d\n", ret);
135 pr_info("Planted fprobe at %s\n", symbol);
140 static void __exit fprobe_exit(void)
142 unregister_fprobe(&sample_probe);
144 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
145 symbol, nhit, sample_probe.nmissed);
148 module_init(fprobe_init)
149 module_exit(fprobe_exit)
150 MODULE_LICENSE("GPL");