aot: Allow running aot binaries directly without calling runtime shim

Currently, even though we make a copy of the runtime shim and then
embed the necessary metadata + bytecode into the binary, you still need
to pass that binary as an argument to the runtime shim in order to run
it (i.e. you need to do 'bpftrace-aotrt <file_name>'). Since the binary
can fully function on its own, we don't need to do this anymore.

This commit makes the executable just look inside itself for the
metadata and bytecode, skipping the need to call bpftrace-aotrt. (i.e.
you can now run the binary with just ./<file_name>.)

src/aot/aot.cpp

@@ -26,7 +26,6 @@
 
 #define AOT_ELF_SECTION ".btaot"
 static constexpr auto AOT_MAGIC = 0xA07;
-static constexpr auto AOT_SHIM_NAME = "bpftrace-aotrt";
 static constexpr auto AOT_SECDATA_TEMPFILE = ".temp_btaot";
 
 // AOT payload will have this header at the beginning. We don't worry about
@@ -190,7 +189,7 @@ int generate(const RequiredResources &resources,
   if (!section)
     return 1;
 
-  auto shim = find_in_path(AOT_SHIM_NAME);
+  auto shim = find_in_path(AOT_SHIM_NAME.data());
   if (!shim) {
     LOG(ERROR) << "Failed to locate " << AOT_SHIM_NAME
                << " shim binary. Is it in $PATH?";

src/aot/aot.h

@@ -9,6 +9,8 @@
 namespace bpftrace {
 namespace aot {
 
+static constexpr std::string_view AOT_SHIM_NAME = "bpftrace-aotrt";
+
 int generate(const RequiredResources &resources,
              const std::string &out,
              void *const elf,

src/aot/aot_main.cpp

@@ -1,3 +1,4 @@
+#include <filesystem>
 #include <fstream>
 #include <getopt.h>
 #include <iostream>
@@ -11,10 +12,10 @@
 
 using namespace bpftrace;
 
-void usage()
+void usage(std::string_view filename)
 {
   // clang-format off
-  std::cerr << "USAGE: bpftrace-aotrt filename" << std::endl;
+  std::cerr << "USAGE: " << filename << " [options]" << std::endl;
   std::cerr << std::endl;
   std::cerr << "OPTIONS:" << std::endl;
   std::cerr << "    -f FORMAT      output format ('text', 'json')" << std::endl;
@@ -70,6 +71,13 @@ int main(int argc, char* argv[])
     option{ nullptr, 0, nullptr, 0 }, // Must be last
   };
 
+  std::filesystem::path p(argv[0]);
+  if (p.filename() == aot::AOT_SHIM_NAME) {
+    LOG(ERROR) << "Runtime shim should not be run directly, please generate a "
+                  "binary using --aot option in bpftrace";
+    return 1;
+  }
+
   while ((c = getopt_long(argc, argv, short_opts, long_opts, nullptr)) != -1) {
     switch (c) {
       case 'o':
@@ -79,7 +87,7 @@ int main(int argc, char* argv[])
         output_format = optarg;
         break;
       case 'h':
-        usage();
+        usage(argv[0]);
         return 0;
       case 'V':
         std::cout << "bpftrace " << BPFTRACE_VERSION << std::endl;
@@ -91,13 +99,13 @@ int main(int argc, char* argv[])
         bt_verbose = true;
         break;
       default:
-        usage();
+        usage(argv[0]);
         return 1;
     }
   }
 
-  if (!argv[optind]) {
-    usage();
+  if (argv[optind]) {
+    usage(argv[0]);
     return 1;
   }
 
@@ -108,7 +116,7 @@ int main(int argc, char* argv[])
     return 1;
 
   BPFtrace bpftrace(std::move(output));
-  int err = aot::load(bpftrace, argv[optind]);
+  int err = aot::load(bpftrace, argv[0]);
   if (err) {
     LOG(ERROR) << "Failed to load AOT script";
     return err;