Make clang tool generate fake main

PiperOrigin-RevId: 809025458
Change-Id: I25e8c330d542b695811103c4df6d3c7d1163e8b3

Author: dvyukov

sandboxed_api/bazel/sapi.bzl

@@ -532,13 +532,15 @@ def cc_sandboxed_library(
         lib_name = wrapper_name,
         sandboxee_hdr_out = name + ".sapi.sandboxee.h.unformatted",
         sandboxee_src_out = name + ".sapi.sandboxee.cc.unformatted",
+        sandboxee_main_out = name + ".sapi.sandboxee_main.cc.unformatted",
         host_src_out = name + ".sapi.host.cc.unformatted",
         sapi_hdr = native.package_name() + "/_sapi_" + name + ".sapi.h",
         **common
     )
 
     _clang_format_file(name + ".sapi.sandboxee.h.unformatted", name + ".sapi.sandboxee.h", **common)
     _clang_format_file(name + ".sapi.sandboxee.cc.unformatted", name + ".sapi.sandboxee.cc", **common)
+    _clang_format_file(name + ".sapi.sandboxee_main.cc.unformatted", name + ".sapi.sandboxee_main.cc", **common)
     _clang_format_file(name + ".sapi.host.cc.unformatted", name + ".sapi.host.cc", **common)
 
     cc_library(
@@ -639,6 +641,7 @@ def _sandboxed_library_gen_impl(ctx):
     args.append("--sapi_name={}".format(ctx.attr.lib_name))
     args.append("--sandboxee_hdr_out={}".format(ctx.outputs.sandboxee_hdr_out.path))
     args.append("--sandboxee_src_out={}".format(ctx.outputs.sandboxee_src_out.path))
+    args.append("--sandboxee_main_out={}".format(ctx.outputs.sandboxee_main_out.path))
     args.append("--host_src_out={}".format(ctx.outputs.host_src_out.path))
     args.append("--sapi_out={}".format(ctx.attr.sapi_hdr))
     args.append("--sapi_limit_scan_depth")
@@ -649,7 +652,12 @@ def _sandboxed_library_gen_impl(ctx):
     progress_msg = "Generating sandboxed library {}.".format(ctx.attr.lib_name)
     ctx.actions.run(
         inputs = cc_ctx.headers.to_list() + cpp_toolchain.all_files.to_list(),
-        outputs = [ctx.outputs.sandboxee_hdr_out, ctx.outputs.sandboxee_src_out, ctx.outputs.host_src_out],
+        outputs = [
+            ctx.outputs.sandboxee_hdr_out,
+            ctx.outputs.sandboxee_src_out,
+            ctx.outputs.sandboxee_main_out,
+            ctx.outputs.host_src_out,
+        ],
         arguments = args,
         mnemonic = "SandboxedLibraryGen",
         progress_message = progress_msg,
@@ -665,6 +673,7 @@ _sandboxed_library_gen = rule(
         "lib_name": attr.string(),
         "sandboxee_hdr_out": attr.output(),
         "sandboxee_src_out": attr.output(),
+        "sandboxee_main_out": attr.output(),
         "host_src_out": attr.output(),
         "sapi_hdr": attr.string(),
         "_generator": make_exec_label(

sandboxed_api/tools/clang_generator/generator_tool.cc

@@ -122,6 +122,13 @@ absl::NoDestructor<llvm::cl::opt<std::string>> g_sandboxee_src_out(
                    "source file."),
     llvm::cl::cat(*g_tool_category));
 
+absl::NoDestructor<llvm::cl::opt<std::string>> g_sandboxee_main_out(
+    "sandboxee_main_out",
+    llvm::cl::desc("Output path of the generated source file containing the "
+                   "stub main function for binary used for system call policy "
+                   "extraction."),
+    llvm::cl::cat(*g_tool_category));
+
 absl::NoDestructor<llvm::cl::opt<std::string>> g_host_src_out(
     "host_src_out",
     llvm::cl::desc(
@@ -214,6 +221,10 @@ absl::Status GeneratorMain(int argc, char* argv[]) {
                           emitter.EmitSandboxeeSrc(options));
     SAPI_RETURN_IF_ERROR(file::SetContents(*g_sandboxee_src_out, sandboxee_src,
                                            file::Defaults()));
+    SAPI_ASSIGN_OR_RETURN(std::string sandboxee_main,
+                          emitter.EmitSandboxeeMain(options));
+    SAPI_RETURN_IF_ERROR(file::SetContents(*g_sandboxee_main_out,
+                                           sandboxee_main, file::Defaults()));
     SAPI_ASSIGN_OR_RETURN(std::string host_src, emitter.EmitHostSrc(options));
     SAPI_RETURN_IF_ERROR(
         file::SetContents(*g_host_src_out, host_src, file::Defaults()));

sandboxed_api/tools/clang_generator/sandboxed_library_emitter.cc

@@ -281,7 +281,7 @@ absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitSandboxeeHdr(
     EmitWrapperDecl(out, *func);
     out += ";\n\n";
   }
-  return Finalize(out, true);
+  return Finalize(out, /*is_header=*/true, /*add_includes=*/true);
 }
 
 absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitSandboxeeSrc(
@@ -315,7 +315,21 @@ absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitSandboxeeSrc(
     }
     out += "}\n\n";
   }
-  return Finalize(out, false);
+  return Finalize(out, /*is_header=*/false, /*add_includes=*/true);
+}
+
+absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitSandboxeeMain(
+    const GeneratorOptions& options) const {
+  std::string out;
+  for (const auto* func : SortedFuncs()) {
+    out += absl::Substitute("extern \"C\" void $0();\n", func->name);
+  }
+  out += "\nint main() {\n";
+  for (const auto* func : SortedFuncs()) {
+    out += absl::Substitute("$0();\n", func->name);
+  }
+  out += "}\n";
+  return Finalize(out, /*is_header=*/false, /*add_includes=*/false);
 }
 
 absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitHostSrc(
@@ -359,7 +373,7 @@ absl::StatusOr<std::string> SandboxedLibraryEmitter::EmitHostSrc(
     }
     out += "}\n\n";
   }
-  return Finalize(out, false);
+  return Finalize(out, /*is_header=*/false, /*add_includes=*/true);
 }
 
 void SandboxedLibraryEmitter::EmitFuncDecl(std::string& out, const Func& func) {
@@ -401,16 +415,18 @@ void SandboxedLibraryEmitter::EmitWrapperDecl(std::string& out,
 }
 
 absl::StatusOr<std::string> SandboxedLibraryEmitter::Finalize(
-    const std::string& body, bool is_header) const {
+    const std::string& body, bool is_header, bool add_includes) const {
   std::string out;
   if (is_header) {
     out.append(kHeaderHeader.data(), kHeaderHeader.size());
   }
   out.append(kCommonHeader.data(), kCommonHeader.size());
-  std::vector<std::string> includes(includes_.begin(), includes_.end());
-  std::sort(includes.begin(), includes.end());
-  for (const auto& inc : includes) {
-    out += absl::Substitute("#include $0\n", inc);
+  if (add_includes) {
+    std::vector<std::string> includes(includes_.begin(), includes_.end());
+    std::sort(includes.begin(), includes.end());
+    for (const auto& inc : includes) {
+      out += absl::Substitute("#include $0\n", inc);
+    }
   }
   out += "\n";
   out += body;

sandboxed_api/tools/clang_generator/sandboxed_library_emitter.h

@@ -38,6 +38,8 @@ class SandboxedLibraryEmitter : public EmitterBase {
       const GeneratorOptions& options) const;
   absl::StatusOr<std::string> EmitSandboxeeSrc(
       const GeneratorOptions& options) const;
+  absl::StatusOr<std::string> EmitSandboxeeMain(
+      const GeneratorOptions& options) const;
   absl::StatusOr<std::string> EmitHostSrc(
       const GeneratorOptions& options) const;
 
@@ -57,8 +59,8 @@ class SandboxedLibraryEmitter : public EmitterBase {
   absl::Status AddFunction(clang::FunctionDecl* decl) override;
   static void EmitFuncDecl(std::string& out, const Func& func);
   static void EmitWrapperDecl(std::string& out, const Func& func);
-  absl::StatusOr<std::string> Finalize(const std::string& body,
-                                       bool is_header) const;
+  absl::StatusOr<std::string> Finalize(const std::string& body, bool is_header,
+                                       bool add_includes) const;
   ArgPtr Convert(absl::string_view name, clang::QualType type);
   std::vector<const Func*> SortedFuncs() const;