Rough solution for Tasks 1, 2, 3

main.go:

	- reading /proc
	- iteration over entries in NNN/maps
	- filter glob-search for "*python3*" in pathname
	- find symbol and its offset in pathnanme
	- calculate offset in memory
	- add pid and offset to map

	TODO: encapsulating this into a module

ebpf.go:

	- added type MapFD int, changing all function on a FD to methods
	  This allows us to enrich the data type going forward

	- added bpf_update_elem() from the manpage ebpf2.
	  .updateElement() is the verbatim wrapper to it.

	- added .Add/.Change/.Set methods, which call .updateElement
	  with specific flags

	TODO: re-implement ebpf.go with pure go, using direct syscalls.

GetRuntimeAddresses/ebpf/ebpf.go

@@ -49,7 +49,17 @@ int bpf_lookup_elem(int fd, const void *key, void *value)
 	return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
 }
 
-// TODO: add insert
+int bpf_update_elem(int fd, const void *key, const void *value, uint64_t flags)
+{
+	union bpf_attr attr = {
+		.map_fd = fd,
+		.key    = (__u64) (unsigned long) key,
+		.value  = (__u64) (unsigned long) value,
+		.flags  = flags,
+	};
+
+	return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
+}
 
 */
 import "C"
@@ -59,18 +69,26 @@ import (
 	"unsafe"
 )
 
+type MapFD int
+
 // CreateMap creates an eBPF map from int->uint64. The file descriptor of the
 // created map is returned.
-func CreateMap() (int, error) {
-	mapFD := C.bpf_create_map(C.BPF_MAP_TYPE_HASH, 4, 8, 64)
-	return int(mapFD), nil
+func CreateMap() (MapFD, error) {
+
+	r, errno := C.bpf_create_map(C.BPF_MAP_TYPE_HASH, 4, 8, 64)
+
+	if r == -1 {
+		return MapFD(r), fmt.Errorf("bpf_create_map with errno %d", errno)
+	}
+
+	return MapFD(r), nil
 }
 
 // GetMap gets the key/value pairs from the specified eBPF map as a Go map
-func GetMap(mapFD int) (map[int]uint64, error) {
+func (mfd MapFD) GetMap() (map[int]uint64, error) {
 	retMap := make(map[int]uint64)
 
-	mapFDC := C.int(mapFD)
+	mapFDC := C.int(mfd)
 	keyC := C.int(0)
 	nextKeyC := C.int(0)
 	valC := C.uint64_t(0)
@@ -94,3 +112,29 @@ func GetMap(mapFD int) (map[int]uint64, error) {
 		keyC = nextKeyC
 	}
 }
+
+func (mfd MapFD) Add(key int, value uint64) error {
+	return mfd.updateElement(key, value, C.BPF_NOEXIST)
+}
+
+func (mfd MapFD) Change(key int, value uint64) error {
+	return mfd.updateElement(key, value, C.BPF_EXIST)
+}
+
+func (mfd MapFD) Set(key int, value uint64) error {
+	return mfd.updateElement(key, value, C.BPF_ANY)
+}
+
+func (mfd MapFD) updateElement(key int, value uint64, flag C.uint64_t) error {
+
+	r, errno := C.bpf_update_elem(C.int(mfd),
+		unsafe.Pointer(&key),
+		unsafe.Pointer(&value),
+		flag)
+
+	if r == -1 {
+		return fmt.Errorf("bpf_update_elem failed with errno %d", errno)
+	}
+
+	return nil
+}

GetRuntimeAddresses/main.go

@@ -56,11 +56,11 @@ func main() {
 		} else if offset, found := searchSymbolIn(pid_s, "*python3*", "_PyRuntime"); !found {
 			continue
 		} else {
-			fmt.Printf("going to set (%d -> 0x%x)\n\n", pid, offset)
+			mapFD.Add(pid, uint64(offset))
 		}
 	}
 
-	mapContents, err := ebpf.GetMap(mapFD)
+	mapContents, err := mapFD.GetMap()
 	if err != nil {
 		fmt.Printf("Failed to get the map contents: %s", err)
 		os.Exit(1)
@@ -161,7 +161,7 @@ func searchSymbolIn(pid, glob, symbol string) (offset uint64, ok bool) {
 
 		memoff := sym.Value - section.Addr + alignedOffset(section)
 
-		fmt.Printf("pid: %s\nsym: %#v\nsection: %#v\nmemoff: 0x%x\narange: %#v\nmap-fileoffset: 0x%x\npathname: %s\n", pid, sym, section, memoff, arange, fileoffset, pathname)
+		// fmt.Printf("pid: %s\nsym: %#v\nsection: %#v\nmemoff: 0x%x\narange: %#v\nmap-fileoffset: 0x%x\npathname: %s\n", pid, sym, section, memoff, arange, fileoffset, pathname)
 
 		// stop when only _one_ is found
 		return arange.start + memoff - fileoffset, true