dump_constants: Add a tool to generate a JSON file with all constants

This change adds a way to export all the necessary constants so that
external tools can compile the policy files.

Bug: chromium:856315
Test: make all

Change-Id: I8637c63b9b09839616aa66ef1714444cb4e124ee

3 files changed, 61 insertions, 1 deletions

diff --git a/.gitignore b/.gitignore
index b500f2a..2414029 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,8 @@
 *.o
 *.a
 
+/constants.json
+
 # Coverage-related files that appear when building with MODE=profiling.
 *.gcno
 *.gcda
@@ -17,6 +19,7 @@
 *.so
 
 # Executables when compiling in-tree.
+/dump_constants
 /libminijail_unittest
 /minijail0
 /minijail0_cli_unittest
diff --git a/Makefile b/Makefile
index 54ee978..d58d2ad 100644
--- a/Makefile
+++ b/Makefile
@@ -55,9 +55,10 @@ CORE_OBJECT_FILES := libminijail.o syscall_filter.o signal_handler.o \
 		libconstants.gen.o libsyscalls.gen.o
 
 all: CC_BINARY(minijail0) CC_LIBRARY(libminijail.so) \
-	CC_LIBRARY(libminijailpreload.so)
+	CC_LIBRARY(libminijailpreload.so) constants.json
 
 parse_seccomp_policy: CXX_BINARY(parse_seccomp_policy)
+dump_constants: CXX_BINARY(dump_constants)
 
 tests: TEST(CXX_BINARY(libminijail_unittest)) \
 	TEST(CXX_BINARY(minijail0_cli_unittest)) \
@@ -141,6 +142,16 @@ CXX_BINARY(parse_seccomp_policy): parse_seccomp_policy.o syscall_filter.o \
 clean: CLEAN(parse_seccomp_policy)
 
 
+CXX_BINARY(dump_constants): dump_constants.o \
+		libconstants.gen.o libsyscalls.gen.o
+clean: CLEAN(dump_constants)
+
+
+constants.json: CXX_BINARY(dump_constants)
+	./dump_constants > $@
+clean: CLEANFILE(constants.json)
+
+
 libsyscalls.gen.o: CPPFLAGS += -I$(SRC)
 
 libsyscalls.gen.o.depends: libsyscalls.gen.c
diff --git a/dump_constants.cc b/dump_constants.cc
new file mode 100644
index 0000000..f33bd5b
--- /dev/null
+++ b/dump_constants.cc
@@ -0,0 +1,46 @@
+/* Copyright 2018 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+// Generate a .json file with all the architecture-specific constants.
+
+#include <cstdint>
+#include <iomanip>
+#include <iostream>
+#include <string>
+
+#include "arch.h"
+#include "libconstants.h"
+#include "libsyscalls.h"
+
+int main() {
+  std::cout << "{\n";
+  std::cout << "  \"arch_nr\": " << ARCH_NR << ",\n";
+  std::cout << "  \"bits\": " << (sizeof(uintptr_t) * 8) << ",\n";
+  std::cout << "  \"syscalls\": {\n";
+  bool first = true;
+  for (const struct syscall_entry* entry = syscall_table; entry->name;
+       ++entry) {
+    if (first)
+      first = false;
+    else
+      std::cout << ",\n";
+    std::cout << "    \"" << entry->name << "\": " << entry->nr;
+  }
+  std::cout << "\n  },\n";
+  std::cout << "  \"constants\": {\n";
+  first = true;
+  for (const struct constant_entry* entry = constant_table; entry->name;
+       ++entry) {
+    if (first)
+      first = false;
+    else
+      std::cout << ",\n";
+    std::cout << "    \"" << entry->name << "\": " << entry->value;
+  }
+  std::cout << "\n  }\n";
+  std::cout << "}\n";
+
+  return 0;
+}