Add name to address ksym helper

Add a helper to translate from kernel name to symbol. As part of this,
slightly refactor the ksym globals (which are internal implementation
and not part of the api) so that there is one array of tuples instead of
two arrays.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/python/bcc/__init__.py

@@ -33,8 +33,8 @@ open_uprobes = {}
 tracefile = None
 TRACEFS = "/sys/kernel/debug/tracing"
 KALLSYMS = "/proc/kallsyms"
-ksym_addrs = []
-ksym_names = []
+ksyms = []
+ksym_names = {}
 ksym_loaded = 0
 
 @atexit.register
@@ -629,7 +629,7 @@ class BPF(object):
 
     @staticmethod
     def _load_kallsyms():
-        global ksym_loaded, ksym_addrs, ksym_names
+        global ksym_loaded, ksyms, ksym_names
         if ksym_loaded:
             return
         try:
@@ -641,19 +641,20 @@ class BPF(object):
             cols = line.split()
             name = cols[2]
             addr = int(cols[0], 16)
-            ksym_addrs.append(addr)
-            ksym_names.append(name)
+            # keep a mapping of names to ksyms index
+            ksym_names[name] = len(ksyms)
+            ksyms.append((name, addr))
         syms.close()
         ksym_loaded = 1
 
     @staticmethod
     def _ksym_addr2index(addr):
-        global ksym_addrs
+        global ksyms
         start = -1
-        end = len(ksym_addrs)
+        end = len(ksyms)
         while end != start + 1:
             mid = int((start + end) / 2)
-            if addr < ksym_addrs[mid]:
+            if addr < ksyms[mid][1]:
                 end = mid
             else:
                 start = mid
@@ -666,12 +667,12 @@ class BPF(object):
         Translate a kernel memory address into a kernel function name, which is
         returned. This is a simple translator that uses /proc/kallsyms.
         """
-        global ksym_names
+        global ksyms
         BPF._load_kallsyms()
         idx = BPF._ksym_addr2index(addr)
         if idx == -1:
             return "[unknown]"
-        return ksym_names[idx]
+        return ksyms[idx][0]
 
     @staticmethod
     def ksymaddr(addr):
@@ -681,13 +682,27 @@ class BPF(object):
         instruction offset as a hexidecimal number, which is returned as a
         string. This is a simple translator that uses /proc/kallsyms.
         """
-        global ksym_addrs, ksym_names
+        global ksyms
         BPF._load_kallsyms()
         idx = BPF._ksym_addr2index(addr)
         if idx == -1:
             return "[unknown]"
-        offset = int(addr - ksym_addrs[idx])
-        return ksym_names[idx] + hex(offset)
+        offset = int(addr - ksyms[idx][1])
+        return ksyms[idx][0] + hex(offset)
+
+    @staticmethod
+    def ksymname(name):
+        """ksymname(name)
+
+        Translate a kernel name into an address. This is the reverse of
+        ksymaddr. Returns -1 when the function name is unknown."""
+
+        global ksyms, ksym_names
+        BPF._load_kallsyms()
+        idx = ksym_names.get(name, -1)
+        if idx == -1:
+            return 0
+        return ksyms[idx][1]
 
     @staticmethod
     def num_open_kprobes():