From 79d849a3a0462ab0a33cbf208e27e28d05eab213 Mon Sep 17 00:00:00 2001
From: Viktor Malik <viktor.malik@gmail.com>
Date: Fri, 3 Mar 2023 08:28:54 +0100
Subject: [PATCH 1/2] Parse kernel configuration

In future, it may (and will) be useful to have access to the running
kernel configuration, e.g. to add config-specific compilation options to
ClangParser.

This adds and fills a new map BPFtrace::kconfig that maps config options
to their values. Both the option name and the value are strings. The
configuration is parsed from one of two sources:
- /boot/config-$(uname -r)
- /proc/config.gz

For testing purposes, the config filename may be passed through the
BPFTRACE_KCONFIG_TEST env variable.
---
 src/bpftrace.h  |  1 +
 src/utils.cpp   | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/utils.h     | 12 ++++++++++++
 tests/utils.cpp | 19 +++++++++++++++++++
 4 files changed, 82 insertions(+)

diff --git a/src/bpftrace.h b/src/bpftrace.h
index a6a8c00b..94587bff 100644
--- a/src/bpftrace.h
+++ b/src/bpftrace.h
@@ -168,6 +168,7 @@ public:
   std::map<libbpf::bpf_func_id, location> helper_use_loc_;
   // mapping traceable functions to modules (or "vmlinux") that they appear in
   FuncsModulesMap traceable_funcs_;
+  KConfig kconfig;
   std::vector<std::unique_ptr<AttachedProbe>> attached_probes_;
 
   std::map<std::string, std::unique_ptr<PCAPwriter>> pcap_writers;
diff --git a/src/utils.cpp b/src/utils.cpp
index 2d9c6695..54c8f054 100644
--- a/src/utils.cpp
+++ b/src/utils.cpp
@@ -28,6 +28,7 @@
 #include <bcc/bcc_syms.h>
 #include <bcc/bcc_usdt.h>
 #include <elf.h>
+#include <zlib.h>
 
 #include <linux/version.h>
 
@@ -178,6 +179,55 @@ StdioSilencer::~StdioSilencer()
   }
 }
 
+KConfig::KConfig()
+{
+  std::vector<std::string> config_locs;
+
+  // Try to get the config from BPFTRACE_KCONFIG_TEST env
+  // If not set, use the set of default locations
+  const char *path_env = std::getenv("BPFTRACE_KCONFIG_TEST");
+  if (path_env)
+    config_locs = { std::string(path_env) };
+  else
+  {
+    struct utsname utsname;
+    if (uname(&utsname) < 0)
+      return;
+    config_locs = {
+      "/boot/config-" + std::string(utsname.release),
+      "/proc/config.gz",
+    };
+  }
+
+  for (auto &path : config_locs)
+  {
+    // gzopen/gzgets handle both uncompressed and compressed files
+    gzFile file = gzopen(path.c_str(), "r");
+    if (!file)
+      continue;
+
+    char buf[4096];
+    while (gzgets(file, buf, sizeof(buf)))
+    {
+      std::string option(buf);
+      if (option.find("CONFIG_") == 0)
+      {
+        // trim trailing '\n'
+        if (option[option.length() - 1] == '\n')
+          option = option.substr(0, option.length() - 1);
+
+        auto split = option.find("=");
+        if (split == std::string::npos)
+          continue;
+
+        config.emplace(option.substr(0, split), option.substr(split + 1));
+      }
+    }
+    gzclose(file);
+  }
+}
+
+
 bool get_uint64_env_var(const std::string &str, uint64_t &dest)
 {
   if (const char* env_p = std::getenv(str.c_str()))
diff --git a/src/utils.h b/src/utils.h
index dccc4504..a76aa161 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -130,6 +130,18 @@ struct DeprecatedName
 typedef std::unordered_map<std::string, std::unordered_set<std::string>>
     FuncsModulesMap;
 
+struct KConfig
+{
+  KConfig();
+  bool has_value(const std::string &name, const std::string &value) const
+  {
+    auto c = config.find(name);
+    return c != config.end() && c->second == value;
+  }
+
+  std::unordered_map<std::string, std::string> config;
+};
+
 static std::vector<DeprecatedName> DEPRECATED_LIST =
 {
 };
diff --git a/tests/utils.cpp b/tests/utils.cpp
index 9ca4ace5..8470745b 100644
--- a/tests/utils.cpp
+++ b/tests/utils.cpp
@@ -222,6 +222,25 @@ TEST(utils, get_cgroup_path_in_hierarchy)
   }
 }
 
+TEST(utils, parse_kconfig)
+{
+  char path[] = "/tmp/configXXXXXX";
+  int fd = mkstemp(path);
+  const std::string config = "# Intro comment\n"
+                             "CONFIG_YES=y\n"
+                             "CONFIG_MOD=m\n"
+                             "CONFIG_VAL=42\n"
+                             "# CONFIG_NO is not set";
+  EXPECT_EQ(write(fd, config.c_str(), config.length()), config.length());
+  setenv("BPFTRACE_KCONFIG_TEST", path, true);
+
+  KConfig kconfig;
+  ASSERT_TRUE(kconfig.has_value("CONFIG_YES", "y"));
+  ASSERT_TRUE(kconfig.has_value("CONFIG_MOD", "m"));
+  ASSERT_TRUE(kconfig.has_value("CONFIG_VAL", "42"));
+  ASSERT_EQ(kconfig.config.find("CONFIG_NO"), kconfig.config.end());
+}
+
 } // namespace utils
 } // namespace test
 } // namespace bpftrace
-- 
2.39.2