[RFC PATCH v2 8/8] [DO NOT MERGE] Out-of-tree: Support wildcard symbol option to sample

Masami Hiramatsu
2022-01-12T14:05:04Z

This is not intended to be merged to upstream code (since this
expose some kernel internal functions just for an example.)

But this is good to show how the fprobe is time-efficient
for registering a probe on thousands of functions.

# time insmod fprobe_example.ko symbol='btrfs_*'
[ 36.130947] fprobe_init: 1028 symbols found
[ 36.177901] fprobe_init: Planted fprobe at btrfs_*
real 0m 0.08s
user 0m 0.00s
sys 0m 0.07s

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
kernel/kallsyms.c | 1 +
kernel/trace/ftrace.c | 1 +
samples/fprobe/fprobe_example.c | 69 ++++++++++++++++++++++++++++++++++-----
3 files changed, 62 insertions(+), 9 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 3011bc33a5ba..d0c4073acbfd 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -246,6 +246,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
}
return 0;
}
+EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);
#endif /* CONFIG_LIVEPATCH */

static unsigned long get_symbol_pos(unsigned long addr,
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d38ae5063be3..feb69ecc5d2c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1580,6 +1580,7 @@ unsigned long ftrace_location(unsigned long ip)
{
return ftrace_location_range(ip, ip);
}
+EXPORT_SYMBOL_GPL(ftrace_location);

/**
* ftrace_text_reserved - return true if range contains an ftrace location
diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
index c28320537f98..df034e00661e 100644
--- a/samples/fprobe/fprobe_example.c
+++ b/samples/fprobe/fprobe_example.c
@@ -12,6 +12,7 @@

#define pr_fmt(fmt) "%s: " fmt, __func__

+#include <linux/glob.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fprobe.h>
@@ -37,16 +38,51 @@ static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_r

static char *symbuf;

+struct sym_search_param {
+ unsigned long *addrs;
+ const char *pat;
+ int cnt;
+};
+
+#define MAX_FPROBE_ENTS (16 * 1024)
+
+static int wildcard_match(void *data, const char *symbol, struct module *mod,
+ unsigned long addr)
+{
+ struct sym_search_param *param = (struct sym_search_param *)data;
+
+ if (glob_match(param->pat, symbol)) {
+ if (!ftrace_location(addr))
+ return 0;
+
+ if (param->addrs)
+ param->addrs[param->cnt] = addr;
+ param->cnt++;
+ if (param->cnt >= MAX_FPROBE_ENTS)
+ return -E2BIG;
+ }
+ return 0;
+}
+
static int __init fprobe_init(void)
{
- const char **syms;
+ struct sym_search_param param = {.pat = symbol, .addrs = NULL, .cnt = 0};
+ unsigned long *addrs = NULL;
+ const char **syms = NULL;
char *p;
int ret, count, i;
+ bool wildcard = false;

sample_probe.entry_handler = sample_entry_handler;
sample_probe.exit_handler = sample_exit_handler;

- if (strchr(symbol, ',')) {
+ if (strchr(symbol, '*')) {
+ kallsyms_on_each_symbol(wildcard_match, &param);
+ count = param.cnt;
+ if (!count)
+ return -ENOENT;
+ wildcard = true;
+ } else if (strchr(symbol, ',')) {
symbuf = kstrdup(symbol, GFP_KERNEL);
if (!symbuf)
return -ENOMEM;
@@ -58,19 +94,31 @@ static int __init fprobe_init(void)
count = 1;
symbuf = symbol;
}
- pr_info("%d symbols found\n", count);

- syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
- if (!syms) {
+ if (wildcard)
+ addrs = kcalloc(count, sizeof(unsigned long), GFP_KERNEL);
+ else
+ syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
+ if (!syms && !addrs) {
ret = -ENOMEM;
goto error;
}

- p = symbuf;
- for (i = 0; i < count; i++)
- syms[i] = strsep(&p, ",");
+ if (wildcard) {
+ param.addrs = addrs;
+ param.cnt = 0;
+
+ kallsyms_on_each_symbol(wildcard_match, &param);
+ count = param.cnt;
+ sample_probe.addrs = addrs;
+ } else {
+ p = symbuf;
+ for (i = 0; i < count; i++)
+ syms[i] = strsep(&p, ",");
+ sample_probe.syms = syms;
+ }
+ pr_info("%d symbols found\n", count);

- sample_probe.syms = syms;
sample_probe.nentry = count;

ret = register_fprobe(&sample_probe);
@@ -82,6 +130,8 @@ static int __init fprobe_init(void)
return 0;

error:
+ kfree(addrs);
+ kfree(syms);
if (symbuf != symbol)
kfree(symbuf);
return ret;
@@ -92,6 +142,7 @@ static void __exit fprobe_exit(void)
unregister_fprobe(&sample_probe);

kfree(sample_probe.syms);
+ kfree(sample_probe.addrs);
if (symbuf != symbol)
kfree(symbuf);