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Date: Fri, 27 Mar 2009 13:17:17 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Masami Hiramatsu <mhiramat@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
systemtap-ml <systemtap@...rces.redhat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH -tip 4/4 V3] tracing: kprobe-tracer plugin supports
fetching symbol value
On Thu, Mar 26, 2009 at 06:59:36PM -0400, Masami Hiramatsu wrote:
> 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");
Looks good too!
Acked-by: Frederic Weisbecker <fweisbec@...il.com>
> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America) Inc.
> Software Solutions Division
>
> e-mail: mhiramat@...hat.com
>
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