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Message-ID: <49CC08D8.6080501@redhat.com>
Date: Thu, 26 Mar 2009 18:59:36 -0400
From: Masami Hiramatsu <mhiramat@...hat.com>
To: Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>
CC: systemtap-ml <systemtap@...rces.redhat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH -tip 4/4 V3] tracing: kprobe-tracer plugin supports fetching
symbol value
Add symbol value fetching support. This allows kprobe tracer to fetch the
value of global variables.
To record some values of symbols, just specify @SYMBOL(e.g. @jiffies).
Offset specifying is also available(e.g. @jiffies+4).
---
Documentation/ftrace.txt | 1
kernel/trace/trace_kprobe.c | 120 +++++++++++++++++++++++++++++++++++++------
2 files changed, 104 insertions(+), 17 deletions(-)
diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
index ddc75af..1ad2e66 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -1336,6 +1336,7 @@ Synopsis of kprobe_probes:
rN : Fetch Nth register (N >= 0)
sN : Fetch Nth entry of stack (N >= 0)
@ADDR : Fetch memory at ADDR (ADDR should be in kernel)
+ @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
aN : Fetch function argument. (N >= 1)(*)
rv : Fetch return value.(**)
rp : Fetch return address.(**)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 68b2833..c22a5c6 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -142,6 +142,55 @@ static unsigned long fetch_ip(struct pt_regs *regs, void *dummy)
return instruction_pointer(regs);
}
+struct symbol_cache {
+ char *symbol;
+ long offset;
+ unsigned long addr;
+};
+
+static unsigned long update_symbol_cache(struct symbol_cache *sc)
+{
+ sc->addr = (unsigned long)kallsyms_lookup_name(sc->symbol);
+ if (sc->addr)
+ sc->addr += sc->offset;
+ return sc->addr;
+}
+
+static void free_symbol_cache(struct symbol_cache *sc)
+{
+ kfree(sc->symbol);
+ kfree(sc);
+}
+
+static struct symbol_cache *alloc_symbol_cache(const char *sym, long offset)
+{
+ struct symbol_cache *sc;
+ if (!sym || strlen(sym) == 0)
+ return NULL;
+ sc = kzalloc(sizeof(struct symbol_cache), GFP_KERNEL);
+ if (!sc)
+ return NULL;
+
+ sc->symbol = kstrdup(sym, GFP_KERNEL);
+ if (!sc->symbol) {
+ kfree(sc);
+ return NULL;
+ }
+ sc->offset = offset;
+
+ update_symbol_cache(sc);
+ return sc;
+}
+
+static unsigned long fetch_symbol(struct pt_regs *regs, void *data)
+{
+ struct symbol_cache *sc = data;
+ if (sc->addr)
+ return fetch_memory(regs, (void *)sc->addr);
+ else
+ return 0;
+}
+
/**
* kprobe_trace_core
@@ -225,6 +274,11 @@ static struct trace_probe *alloc_trace_probe(const char *symbol)
static void free_trace_probe(struct trace_probe *tp)
{
+ int i;
+ for (i = 0; i < tp->nr_args; i++)
+ if (tp->args[i].func == fetch_symbol)
+ free_symbol_cache(tp->args[i].data);
+
kfree(tp->symbol);
kfree(tp);
}
@@ -258,6 +312,32 @@ static void unregister_trace_probe(struct trace_probe *tp)
list_del(&tp->list);
}
+/* Split symbol and offset. */
+static int split_symbol_offset(char *symbol, long *offset)
+{
+ char *tmp;
+ int ret;
+
+ if (!offset)
+ return -EINVAL;
+
+ tmp = strchr(symbol, '+');
+ if (!tmp)
+ tmp = strchr(symbol, '-');
+
+ if (tmp) {
+ /* skip sign because strict_strtol doesn't accept '+' */
+ ret = strict_strtol(tmp + 1, 0, offset);
+ if (ret)
+ return ret;
+ if (*tmp == '-')
+ *offset = -(*offset);
+ *tmp = '\0';
+ } else
+ *offset = 0;
+ return 0;
+}
+
#define PARAM_MAX_ARGS 16
#define PARAM_MAX_REGS MAX_REG_NUM
#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
@@ -273,6 +353,7 @@ static int create_trace_probe(int argc, char **argv)
* rN : fetch Nth of register (pt_regs + N) (N:0-)
* sN : fetch Nth of stack (N:0-)
* @ADDR : fetch memory at ADDR (ADDR should be in kernel)
+ * @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
*/
struct trace_probe *tp;
struct kprobe *kp;
@@ -305,19 +386,9 @@ static int create_trace_probe(int argc, char **argv)
/* a symbol specified */
symbol = argv[1];
/* TODO: support .init module functions */
- tmp = strchr(symbol, '+');
- if (!tmp)
- tmp = strchr(symbol, '-');
-
- if (tmp) {
- /* skip sign because strict_strtol doesn't accept '+' */
- ret = strict_strtol(tmp + 1, 0, &offset);
- if (ret)
- return ret;
- if (*tmp == '-')
- offset = -offset;
- *tmp = '\0';
- }
+ ret = split_symbol_offset(symbol, &offset);
+ if (ret)
+ return ret;
if (offset && is_return)
return -EINVAL;
}
@@ -383,11 +454,23 @@ static int create_trace_probe(int argc, char **argv)
tp->args[i].data = (void *)param;
}
break;
- case '@': /* memory */
- ret = strict_strtoul(tmp + 1, 0, ¶m);
- if (!ret) {
+ case '@': /* memory or symbol */
+ if (isdigit(tmp[1])) {
+ ret = strict_strtoul(tmp + 1, 0, ¶m);
+ if (ret)
+ break;
tp->args[i].func = fetch_memory;
tp->args[i].data = (void *)param;
+ } else {
+ ret = split_symbol_offset(tmp + 1, &offset);
+ if (ret)
+ break;
+ tp->args[i].data = alloc_symbol_cache(tmp + 1,
+ offset);
+ if (tp->args[i].data)
+ tp->args[i].func = fetch_symbol;
+ else
+ ret = -EINVAL;
}
break;
default:
@@ -466,7 +549,10 @@ static int probes_seq_show(struct seq_file *m, void *v)
seq_printf(m, " s%lu", (unsigned long)tp->args[i].data);
else if (tp->args[i].func == fetch_memory)
seq_printf(m, " @0x%p", tp->args[i].data);
- else if (tp->args[i].func == fetch_retvalue)
+ else if (tp->args[i].func == fetch_symbol) {
+ struct symbol_cache *sc = tp->args[i].data;
+ seq_printf(m, " @%s%+ld", sc->symbol, sc->offset);
+ } else if (tp->args[i].func == fetch_retvalue)
seq_printf(m, " rv");
else if (tp->args[i].func == fetch_ip)
seq_printf(m, " rp");
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@...hat.com
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