symbol-index is a host tool that manipulates the symbol-index file, which is typically located at ~/.fuchsia/debug/symbol-index. This file stores the locations of debug symbols from multiple source code checkouts on the local machine, thus debugging tools can read symbols across different checkouts.
A symbol-index could contain multiple lines. Each line could contain one or two paths, separated by “\t”. The first path points to the debug symbols, either in ids.txt format or .build-id directory format. The optional second path points to the build directory, which is used by debugging tools to lookup source code.
For example, a Fuchsia checkout located at /home/me/fuchsia could have the following content in the file.
/home/me/fuchsia/out/default/.build-id /home/me/fuchsia/out/default /home/me/fuchsia/out/default.zircon/.build-id /home/me/fuchsia/out/default.zircon /home/me/fuchsia/prebuilt/.build-id /home/me/fuchsia/prebuilt/third_party/clang/mac-x64/lib/debug/.build-id