tracing: expose current->comm to [ku]probe events

ftrace is very quick to give up on saving the task command line (see
`trace_save_cmdline()`). The workaround for events which really care
about the command line is to explicitly assign it as part of the entry.
However, this doesn't work for kprobe events, as there's no
straightforward way to get access to current->comm. Add a kprobe/uprobe
event variable $comm which provides exactly that.

Link: http://lkml.kernel.org/r/f59b472033b943a370f5f48d0af37698f409108f.1465435894.git.osandov@fb.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index d68ea5fc812b0fdffc11085a3966c39d8b6f58e8..ea52ec1f8484353b904431a59f4f2e6cedce5830 100644 (file)
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -40,6 +40,7 @@ Synopsis of kprobe_events
   $stackN      : Fetch Nth entry of stack (N >= 0)
   $stack       : Fetch stack address.
   $retval      : Fetch return value.(*)
+  $comm                : Fetch current task comm.
   +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
   NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
   FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
@@ -62,6 +63,8 @@ offset, and container-size (usually 32). The syntax is;
 
  b<bit-width>@<bit-offset>/<container-size>
 
+For $comm, the default type is "string"; any other type is invalid.
+
 
 Per-Probe Event Filtering
 -------------------------

diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
index f1cf9a34ad9d714cc87f4dcf36b2b996e551403e..72d1cd4f7bf3b2a3098f6b4f87fac3a91c859716 100644 (file)
--- a/Documentation/trace/uprobetracer.txt
+++ b/Documentation/trace/uprobetracer.txt
@@ -36,6 +36,7 @@ Synopsis of uprobe_tracer
    $stackN     : Fetch Nth entry of stack (N >= 0)
    $stack      : Fetch stack address.
    $retval     : Fetch return value.(*)
+   $comm       : Fetch current task comm.
    +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
    NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
    FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
@@ -57,6 +58,8 @@ offset, and container-size (usually 32). The syntax is;
 
  b<bit-width>@<bit-offset>/<container-size>
 
+For $comm, the default type is "string"; any other type is invalid.
+
 
 Event Profiling
 ---------------

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5546eec0505f7e111fa5b64d88dcc7806588dace..9aedb0b06683765f4293eb750465ed5849c2902f 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -587,6 +587,7 @@ static int create_trace_kprobe(int argc, char **argv)
         *  $retval     : fetch return value
         *  $stack      : fetch stack address
         *  $stackN     : fetch Nth of stack (N:0-)
+        *  $comm       : fetch current task comm
         *  @ADDR       : fetch memory at ADDR (ADDR should be in kernel)
         *  @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
         *  %REG        : fetch register REG

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 1d372fa6fefb7b44b8c3c38f4436621070ba0da7..74e80a582c28988fbc0227453378d36bf4346999 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -218,6 +218,28 @@ free_bitfield_fetch_param(struct bitfield_fetch_param *data)
        kfree(data);
 }
 
+void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs,
+                                         void *data, void *dest)
+{
+       int maxlen = get_rloc_len(*(u32 *)dest);
+       u8 *dst = get_rloc_data(dest);
+       long ret;
+
+       if (!maxlen)
+               return;
+
+       ret = strlcpy(dst, current->comm, maxlen);
+       *(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
+}
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string));
+
+void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs,
+                                              void *data, void *dest)
+{
+       *(u32 *)dest = strlen(current->comm) + 1;
+}
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size));
+
 static const struct fetch_type *find_fetch_type(const char *type,
                                                const struct fetch_type *ftbl)
 {
@@ -348,6 +370,11 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
                        }
                } else
                        ret = -EINVAL;
+       } else if (strcmp(arg, "comm") == 0) {
+               if (strcmp(t->name, "string") != 0 &&
+                   strcmp(t->name, "string_size") != 0)
+                       return -EINVAL;
+               f->fn = t->fetch[FETCH_MTD_comm];
        } else
                ret = -EINVAL;
 
@@ -522,6 +549,12 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
                arg[t - parg->comm] = '\0';
                t++;
        }
+       /*
+        * The default type of $comm should be "string", and it can't be
+        * dereferenced.
+        */
+       if (!t && strcmp(arg, "$comm") == 0)
+               t = "string";
        parg->type = find_fetch_type(t, ftbl);
        if (!parg->type) {
                pr_info("Unsupported type: %s\n", t);

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index f6398db0911424cca72031a7a5831d505fae71b7..45400ca5ded1acf673d713851f930425b1d20849 100644 (file)
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -102,6 +102,7 @@ enum {
        FETCH_MTD_reg = 0,
        FETCH_MTD_stack,
        FETCH_MTD_retval,
+       FETCH_MTD_comm,
        FETCH_MTD_memory,
        FETCH_MTD_symbol,
        FETCH_MTD_deref,
@@ -183,6 +184,14 @@ DECLARE_BASIC_FETCH_FUNCS(bitfield);
 #define fetch_bitfield_string                  NULL
 #define fetch_bitfield_string_size             NULL
 
+/* comm only makes sense as a string */
+#define fetch_comm_u8          NULL
+#define fetch_comm_u16         NULL
+#define fetch_comm_u32         NULL
+#define fetch_comm_u64         NULL
+DECLARE_FETCH_FUNC(comm, string);
+DECLARE_FETCH_FUNC(comm, string_size);
+
 /*
  * Define macro for basic types - we don't need to define s* types, because
  * we have to care only about bitwidth at recording time.
@@ -213,6 +222,7 @@ DEFINE_FETCH_##method(u64)
 ASSIGN_FETCH_FUNC(reg, ftype),                         \
 ASSIGN_FETCH_FUNC(stack, ftype),                       \
 ASSIGN_FETCH_FUNC(retval, ftype),                      \
+ASSIGN_FETCH_FUNC(comm, ftype),                                \
 ASSIGN_FETCH_FUNC(memory, ftype),                      \
 ASSIGN_FETCH_FUNC(symbol, ftype),                      \
 ASSIGN_FETCH_FUNC(deref, ftype),                       \