tracing/kprobes: Add bitfield type

Add bitfield type for tracing arguments on kprobe-tracer.  The syntax of
a bitfield type is:

 b<bit-size>@<bit-offset>/<container-size>

e.g.

Accessing 2 bits-width field with 4 bits-offset in 32 bits-width data at
4 bytes offseted from the address pointed by AX register:

 +4(%ax):b2@4/32

Since the width of container data depends on the arch, so I just added
the container-size at the end.

Cc: 2nddept-manager@sdl.hitachi.co.jp
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20110204125205.9507.11363.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 118 insertions, 2 deletions

diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index 5f77d94598dd..6d27ab8d6e9f 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -42,11 +42,25 @@ Synopsis of kprobe_events
   +|-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
-                  (u8/u16/u32/u64/s8/s16/s32/s64) and string are supported.
+                  (u8/u16/u32/u64/s8/s16/s32/s64), "string" and bitfield
+                  are supported.
 
   (*) only for return probe.
   (**) this is useful for fetching a field of data structures.
 
+Types
+-----
+Several types are supported for fetch-args. Kprobe tracer will access memory
+by given type. Prefix 's' and 'u' means those types are signed and unsigned
+respectively. Traced arguments are shown in decimal (signed) or hex (unsigned).
+String type is a special type, which fetches a "null-terminated" string from
+kernel space. This means it will fail and store NULL if the string container
+has been paged out.
+Bitfield is another special type, which takes 3 parameters, bit-width, bit-
+offset, and container-size (usually 32). The syntax is;
+
+ b<bit-width>@<bit-offset>/<container-size>
+
 
 Per-Probe Event Filtering
 -------------------------
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c6ed88660856..ccdc542022c3 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -353,6 +353,43 @@ static __kprobes void free_deref_fetch_param(struct deref_fetch_param *data)
         kfree(data);
 }
 
+/* Bitfield fetch function */
+struct bitfield_fetch_param {
+        struct fetch_param orig;
+        unsigned char hi_shift;
+        unsigned char low_shift;
+};
+
+#define DEFINE_FETCH_bitfield(type)                                     \
+static __kprobes void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs,\
+                                            void *data, void *dest)     \
+{                                                                       \
+        struct bitfield_fetch_param *bprm = data;                       \
+        type buf = 0;                                                   \
+        call_fetch(&bprm->orig, regs, &buf);                            \
+        if (buf) {                                                      \
+                buf <<= bprm->hi_shift;                                 \
+                buf >>= bprm->low_shift;                                \
+        }                                                               \
+        *(type *)dest = buf;                                            \
+}
+DEFINE_BASIC_FETCH_FUNCS(bitfield)
+#define fetch_bitfield_string NULL
+#define fetch_bitfield_string_size NULL
+
+static __kprobes void
+free_bitfield_fetch_param(struct bitfield_fetch_param *data)
+{
+        /*
+         * Don't check the bitfield itself, because this must be the
+         * last fetch function.
+         */
+        if (CHECK_FETCH_FUNCS(deref, data->orig.fn))
+                free_deref_fetch_param(data->orig.data);
+        else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn))
+                free_symbol_cache(data->orig.data);
+        kfree(data);
+}
 /* Default (unsigned long) fetch type */
 #define __DEFAULT_FETCH_TYPE(t) u##t
 #define _DEFAULT_FETCH_TYPE(t) __DEFAULT_FETCH_TYPE(t)
@@ -367,6 +404,7 @@ enum {
         FETCH_MTD_memory,
         FETCH_MTD_symbol,
         FETCH_MTD_deref,
+        FETCH_MTD_bitfield,
         FETCH_MTD_END,
 };
 
@@ -387,6 +425,7 @@ ASSIGN_FETCH_FUNC(retval, ftype),			\
 ASSIGN_FETCH_FUNC(memory, ftype),                       \
 ASSIGN_FETCH_FUNC(symbol, ftype),                       \
 ASSIGN_FETCH_FUNC(deref, ftype),                        \
+ASSIGN_FETCH_FUNC(bitfield, ftype),                     \
           }                                             \
         }
 
@@ -430,9 +469,33 @@ static const struct fetch_type *find_fetch_type(const char *type)
         if (!type)
                 type = DEFAULT_FETCH_TYPE_STR;
 
+        /* Special case: bitfield */
+        if (*type == 'b') {
+                unsigned long bs;
+                type = strchr(type, '/');
+                if (!type)
+                        goto fail;
+                type++;
+                if (strict_strtoul(type, 0, &bs))
+                        goto fail;
+                switch (bs) {
+                case 8:
+                        return find_fetch_type("u8");
+                case 16:
+                        return find_fetch_type("u16");
+                case 32:
+                        return find_fetch_type("u32");
+                case 64:
+                        return find_fetch_type("u64");
+                default:
+                        goto fail;
+                }
+        }
+
         for (i = 0; i < ARRAY_SIZE(fetch_type_table); i++)
                 if (strcmp(type, fetch_type_table[i].name) == 0)
                         return &fetch_type_table[i];
+fail:
         return NULL;
 }
 
@@ -586,7 +649,9 @@ error:
 
 static void free_probe_arg(struct probe_arg *arg)
 {
-        if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
+        if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn))
+                free_bitfield_fetch_param(arg->fetch.data);
+        else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn))
                 free_deref_fetch_param(arg->fetch.data);
         else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn))
                 free_symbol_cache(arg->fetch.data);
@@ -806,6 +871,41 @@ static int __parse_probe_arg(char *arg, const struct fetch_type *t,
         return ret;
 }
 
+#define BYTES_TO_BITS(nb)       ((BITS_PER_LONG * (nb)) / sizeof(long))
+
+/* Bitfield type needs to be parsed into a fetch function */
+static int __parse_bitfield_probe_arg(const char *bf,
+                                      const struct fetch_type *t,
+                                      struct fetch_param *f)
+{
+        struct bitfield_fetch_param *bprm;
+        unsigned long bw, bo;
+        char *tail;
+
+        if (*bf != 'b')
+                return 0;
+
+        bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
+        if (!bprm)
+                return -ENOMEM;
+        bprm->orig = *f;
+        f->fn = t->fetch[FETCH_MTD_bitfield];
+        f->data = (void *)bprm;
+
+        bw = simple_strtoul(bf + 1, &tail, 0);  /* Use simple one */
+        if (bw == 0 || *tail != '@')
+                return -EINVAL;
+
+        bf = tail + 1;
+        bo = simple_strtoul(bf, &tail, 0);
+        if (tail == bf || *tail != '/')
+                return -EINVAL;
+
+        bprm->hi_shift = BYTES_TO_BITS(t->size) - (bw + bo);
+        bprm->low_shift = bprm->hi_shift + bo;
+        return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0;
+}
+
 /* String length checking wrapper */
 static int parse_probe_arg(char *arg, struct trace_probe *tp,
                            struct probe_arg *parg, int is_return)
@@ -835,6 +935,8 @@ static int parse_probe_arg(char *arg, struct trace_probe *tp,
         parg->offset = tp->size;
         tp->size += parg->type->size;
         ret = __parse_probe_arg(arg, parg->type, &parg->fetch, is_return);
+        if (ret >= 0)
+                ret = __parse_bitfield_probe_arg(t, parg->type, &parg->fetch);
         if (ret >= 0) {
                 parg->fetch_size.fn = get_fetch_size_function(parg->type,
                                                               parg->fetch.fn);