How to update the binaries other than protoc-linux-x86_64.exe:

1. Go to http://search.maven.org/
2. Search for g:“com.google.protobuf”
3. Download the “jar” link from protobuf-java.
4. Download all binaries from “protoc”.
5. Strip version number from protoc files: for i in *.exe; do mv $i $(echo $i | sed s/3.0.0-beta-2-//); done
6. Set executable bit: chmod +x *.exe
7. Update third_party/BUILD to point to the new jar file.
8. Done.

The 64-bit Linux version of the proto compiler is linked statically. To update it, do the following steps on an x86_64 machine:

1. git clone http://github.com/google/protobuf.git
2. git checkout <commithash> (current is d5fb408d or 3.0.0-beta-2)
3. ./autogen.sh
4. LDFLAGS=-static ./configure
5. Change LDFLAGS = -static to LDFLAGS = -all-static in src/Makefile.
6. make
7. cp src/protoc <Bazel tree>/third_party/protobuf/protoc-linux-x86_64.exe .

How to update protobuf.bzl and the src/ directory:

1. git clone http://github.com/google/protobuf.git
2. git checkout <commithash> (current is d5fb408d or 3.0.0-beta-2)
3. mkdir -p third_party/protobuf/src/google in the root of the Bazel tree.
4. cp -R <root of protobuf tree>/src/google/protobuf third_party/protobuf/src/google
5. Update rules in third_party/protobuf/BUILD with the rules in the protobuf repository.
6. Done.

How to update protoc-mingw.exe: This is pretty much the same steps as for x86_64 above, but they need to be done from MingW shell on Windows machine ([https://sourceforge.net/projects/msys2/files/]).

1. git clone http://github.com/google/protobuf.git
2. git checkout <commithash> (current is d5fb408d or 3.0.0-beta-2)
3. ./autogen.sh
4. make
5. cp src/protoc.exe <Bazel tree>/third_party/protobuf/protoc-mingw.exe .

How to update anything else in this directory: follow usual procedure as described on https://www.bazel.io/contributing.html