Document the need to export main. Closes #23.

.circleci/config.yml

@@ -26,6 +26,7 @@ jobs:
               $NIXRUN "bazel run clotestbin"
               $NIXRUN "bazel run clotestbin-cc"
               $NIXRUN "bazel run clotestbin-cc-norunfiles"
+              $NIXRUN "bazel run clotestbin-cc-pie"
 
 workflows:
   version: 2

BUILD

@@ -120,6 +120,20 @@ binary_closure(
     src = "libhello-cc-norunfiles.so",
 )
 
+cc_binary(
+    name = "hello-cc-pie",
+    srcs = ["src/test/cc/hello/main.c"],
+    linkopts = ["-pie", "-Wl,--dynamic-list", "main-symbol-list.ld"],
+	deps = ["main-symbol-list.ld"],
+    testonly = True,
+)
+
+binary_closure(
+    name = "clotestbin-cc-pie",
+    testonly = True,
+    src = "hello-cc-pie",
+)
+
 sh_binary(
     name = "deps",
     srcs = ["src/main/bash/deps.sh"],

README.md

@@ -14,10 +14,10 @@ of the result as a poor man's container image. Compared to containers:
 
 Clodl can be used to build binary closures or library closures.
 
-A binary closure is made from an executable and can be executed.
-In practice, the binary closure is a zip file appended to a script
-that uncompresses the file to a temporary folder and has the
-executable invoked.
+A binary closure is made from an executable or a shared library
+defining symbol `main` and can be executed. In practice, the binary
+closure is a zip file appended to a script that uncompresses the file
+to a temporary folder and has `main` invoked.
 
 A library closure is a zip file containing the shared libraries in
 the closure, and provides a top-level library which depends on all of
@@ -58,9 +58,9 @@ haskell_binary(
     name = "hello-hs",
     srcs = ["src/test/haskell/hello/Main.hs"],
     compiler_flags = [
-        "-threaded",
         "-dynamic",
         "-pie",
+        "-rdynamic", # or "-Wl,--dynamic-list", "main-symbol-list.ld"
     ],
 	...
 )
@@ -71,7 +71,7 @@ binary_closure(
 )
 ```
 
-The [BUILD file](BUILD) has a complete example.
+The [BUILD file](BUILD) has complete examples.
 
 [bazel]: https://bazel.build
 [bazel-rules]: https://docs.bazel.build/versions/master/skylark/rules.html

clodl/clodl.bzl

@@ -430,25 +430,33 @@ def library_closure(name, srcs, outzip = "", excludes = [], executable = False,
 def binary_closure(name, src, excludes = [], **kwargs):
     """
     Produces a zip file containing a closure of all the shared libraries needed
-    to load the given executable. The zipfile is prepended with a script that
-    uncompresses the zip file and executes the binary.
+    to load the given position independent executable or shared library defining
+    symbol main. The zipfile is prepended with a script that uncompresses the
+    zip file and executes main.
 
     Args:
       name: A unique name for this rule
-      src: The executable binary
+      src: The position independent executable or a shared library.
       excludes: Same purpose as in library_closure
 
     Example:
       ```bzl
+      cc_binary(
+          name = "hello-cc",
+          srcs = ["src/test/cc/hello/main.c"],
+          linkopts = ["-pie", "-Wl,--dynamic-list", "main-symbol-list.ld"],
+          deps = ["main-symbol-list.ld"],
+      )
+
       binary_closure(
           name = "closure"
-          src = ":exe"
+          src = "hello-cc"
           excludes = ["libexclude_this\.so", "libthis_too\.so"]
           ...
       )
       ```
       The zip file closure is created, with all the
-      shared libraries required by ":exe" except those in excludes.
+      shared libraries required by "hello-cc" except those in excludes.
     """
     zip_name = "%s-closure" % name
     library_closure(

main-symbol-list.ld

@@ -0,0 +1,3 @@
+{
+    main;
+};