diff --git a/tools/cpp/emscripten/BUILD b/tools/cpp/emscripten/BUILD
index dd304e1..6a67e4f 100644
--- a/tools/cpp/emscripten/BUILD
+++ b/tools/cpp/emscripten/BUILD
@@ -1,26 +1,46 @@
 package(default_visibility = ["//visibility:public"])
 
+_minimum_fileset = [
+    "emar.sh",
+    "emcc.sh",
+    "@emscripten_clang//:all",
+    "@emscripten_toolchain//:all",
+    "@nodejs//:bin/node",
+]
+
+filegroup(
+    name = "minimum_files",
+    srcs = _minimum_fileset,
+)
+
 filegroup(
     name = "all",
-    srcs = [
-        "emar.sh",
-        "emcc.sh",
+    srcs = _minimum_fileset + [
         ":emscripten_cache_content",
-        "@emscripten_clang//:all",
-        "@emscripten_toolchain//:all",
-        "@nodejs//:bin/node",
     ],
 )
 
-# TODO(james): There is a set of static files that emscripten will always
-# attempt to either rebuild or source from a cache. Ideally, we would make
-# the build of these files part of the normal build process; however, the
-# emscripten compiler handles sandboxing poorly for these files and so it
-# is simplest to just manually run emscripten outside of the sandbox and
-# copy over the cache folder for now.
+# A list of all the cached libraries generad and used by emscripten.
+_libs = \
+    ["emscripten_cache/asmjs/" + lib for lib in [
+        "generated_struct_info.json",
+        "libc.bc",
+        "libcompiler_rt.a",
+        "libc-wasm.bc",
+        "libpthreads_stub.bc",
+        "libhtml5.bc",
+        "libdlmalloc.bc",
+        "libal.bc",
+        "libc++_noexcept.a",
+        "libc++abi.bc",
+        "libgl-webgl2.bc",
+        "libgl.bc",
+        "libc-extras.bc",
+    ]]
+
 filegroup(
     name = "emscripten_cache_content",
-    srcs = glob(["emscripten_cache/**/*"]),
+    srcs = glob(["emscripten_cache/**/*"]) + _libs,
 )
 
 cc_toolchain(
@@ -36,3 +56,22 @@
     strip_files = ":empty",
     supports_param_files = 0,
 )
+
+# TODO(james): Currently, this gets built with the host configuration.
+# Currently, that doesn't actually impact the build since there's nothing that
+# affects how the genrule is run. However, that also means that changing
+# the configuration (and thus the flags that may be passed to the C++
+# compiler) will not change how these cache files are generated.
+genrule(
+    name = "gencache",
+    # Note that foo.o is just some arbitrary .o file. I had trouble getting
+    # emscripten to work properly when pointed at a literally empty file, but
+    # the exact contents of the .o aren't particularly important.
+    srcs = [":foo.o"],
+    outs = _libs,
+    cmd = "$(location gencache.sh) $(OUTS)",
+    tools = [
+        ":gencache.sh",
+        ":minimum_files",
+    ],
+)
diff --git a/tools/cpp/emscripten/emcc.sh b/tools/cpp/emscripten/emcc.sh
index 52ed893..814cd04 100755
--- a/tools/cpp/emscripten/emcc.sh
+++ b/tools/cpp/emscripten/emcc.sh
@@ -25,15 +25,17 @@
 
 # Prepare the cache content so emscripten doesn't try to rebuild it all the time
 cache_source=tools/cpp/emscripten/emscripten_cache
-if [ -d toolchain/emscripten_cache ]; then
-  cache_source=toolchain/emscripten_cache
+# TODO(james): How do I avoid hardcoding this path? This is needed to make
+# gencache.sh work properly and to have it put the files in the correct spot.
+if [ -d bazel-out/host/bin/tools/cpp/emscripten/emscripten_cache ]; then
+  cache_source=bazel-out/host/bin/tools/cpp/emscripten/emscripten_cache
 elif [ -d external/rules_emscripten/toolchain/emscripten_cache ]; then
   cache_source=external/rules_emscripten/toolchain/emscripten_cache
 fi
 (
   cd tmp/emscripten_cache;
   for n in "../../$cache_source"/*;do
-    ln -s "$n"
+    ln -f -s "$n"
   done
 )
 
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/binaryen_tag_version_82.txt b/tools/cpp/emscripten/emscripten_cache/asmjs/binaryen_tag_version_82.txt
deleted file mode 100644
index 01e1f09..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/binaryen_tag_version_82.txt
+++ /dev/null
@@ -1 +0,0 @@
-version_82
\ No newline at end of file
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/generated_struct_info.json b/tools/cpp/emscripten/emscripten_cache/asmjs/generated_struct_info.json
deleted file mode 100644
index 1e636fd..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/generated_struct_info.json
+++ /dev/null
@@ -1 +0,0 @@
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diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/libc-wasm.bc b/tools/cpp/emscripten/emscripten_cache/asmjs/libc-wasm.bc
deleted file mode 100644
index 50f7172..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/libc-wasm.bc
+++ /dev/null
Binary files differ
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/libc.bc b/tools/cpp/emscripten/emscripten_cache/asmjs/libc.bc
deleted file mode 100644
index 7f4adf9..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/libc.bc
+++ /dev/null
Binary files differ
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/libcompiler_rt.a b/tools/cpp/emscripten/emscripten_cache/asmjs/libcompiler_rt.a
deleted file mode 100644
index 9468549..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/libcompiler_rt.a
+++ /dev/null
Binary files differ
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/libdlmalloc.bc b/tools/cpp/emscripten/emscripten_cache/asmjs/libdlmalloc.bc
deleted file mode 100644
index def54c3..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/libdlmalloc.bc
+++ /dev/null
Binary files differ
diff --git a/tools/cpp/emscripten/emscripten_cache/asmjs/libpthreads_stub.bc b/tools/cpp/emscripten/emscripten_cache/asmjs/libpthreads_stub.bc
deleted file mode 100644
index b5205d0..0000000
--- a/tools/cpp/emscripten/emscripten_cache/asmjs/libpthreads_stub.bc
+++ /dev/null
Binary files differ
diff --git a/tools/cpp/emscripten/foo.o b/tools/cpp/emscripten/foo.o
new file mode 100755
index 0000000..28c06de
--- /dev/null
+++ b/tools/cpp/emscripten/foo.o
Binary files differ
diff --git a/tools/cpp/emscripten/gencache.sh b/tools/cpp/emscripten/gencache.sh
new file mode 100755
index 0000000..d8391d8
--- /dev/null
+++ b/tools/cpp/emscripten/gencache.sh
@@ -0,0 +1,13 @@
+#!/bin/bash
+# This script forces generation of all the necessary cache files from emscripten.
+export EMCC_FORCE_STDLIBS=1
+# Run with WEBGL2 enabled and not, as the compiler will only generate one of the
+# webgl libraries at once.
+tools/cpp/emscripten/emcc.sh -o foo.html.tar tools/cpp/emscripten/foo.o -s 'USE_WEBGL2=1' -no-canonical-prefixes
+tools/cpp/emscripten/emcc.sh -o foo.html.tar tools/cpp/emscripten/foo.o -s 'USE_WEBGL2=0' -no-canonical-prefixes
+for OUTPUT in $@
+do
+  if [ ! -f ${OUTPUT} ]; then
+    cp -f tmp/emscripten_cache/asmjs/$(basename ${OUTPUT}) ${OUTPUT}
+  fi
+done