refactor: Make base_attach_impl into a header-only library fix eunomia-bpf#233 (eunomia-bpf#245)

* refactor: Make base_attach_impl into a header-only library fix eunomia-bpf#233
    * deleted source files from base_attach_impl
    * moved functional codes to header files
    * handled thread_local variables with inline specifier
    * modified CMakeLists to reflect the changes

* formatted base_attach_impl code

---------

Co-authored-by: fr0m_scratch <[email protected]>
Co-authored-by: fr0m_scratch <[email protected]>

Author: 3 people

attach/base_attach_impl/CMakeLists.txt

@@ -1,15 +1,14 @@
+add_library(bpftime_base_attach_impl INTERFACE)
 
+set(BASE_ATTACH_IMPL_INCLUDE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    CACHE STRING "Include path of base_attach_impl")
 
-add_library(bpftime_base_attach_impl STATIC 
-    base_attach_impl.cpp
-    attach_private_data.cpp
-)
-
-set(BASE_ATTACH_IMPL_INCLUDE ${CMAKE_CURRENT_SOURCE_DIR} CACHE STRING "Include path of base_attach_impl")
+target_include_directories(bpftime_base_attach_impl
+                           INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
 
 add_dependencies(bpftime_base_attach_impl spdlog::spdlog)
 
-target_link_libraries(bpftime_base_attach_impl PRIVATE spdlog::spdlog)
-target_include_directories(bpftime_base_attach_impl PRIVATE ${SPDLOG_INCLUDE})
+target_link_libraries(bpftime_base_attach_impl INTERFACE spdlog::spdlog)
 
 set_property(TARGET bpftime_base_attach_impl PROPERTY CXX_STANDARD 20)

attach/base_attach_impl/attach_private_data.cpp

@@ -2,19 +2,27 @@
 #define _BPFTIME_ATTACH_PRIVATE_DATA_HPP
 
 #include <string_view>
+#include "spdlog/spdlog.h"
+#include <stdexcept>
 namespace bpftime
 {
 namespace attach
 {
 // A base class for all attach-independent private data
 struct attach_private_data {
-	virtual ~attach_private_data();
+	virtual ~attach_private_data(){};
 	// Initialize this private data structure from a string.
 	// This function should be implemented by things like
 	// `uprobe_attach_private_data` or `syscall_attach_private_data` or
-	// other ones. In this way, we provide a unified interface to create private data
-	// for different attaches
-	virtual int initialize_from_string(const std::string_view &sv);
+	// other ones. In this way, we provide a unified interface to create
+	// private data for different attaches.
+	virtual int initialize_from_string(const std::string_view &sv)
+	{
+		SPDLOG_ERROR(
+			"Not implemented: attach_private_data::initialize_from_string");
+		throw std::runtime_error(
+			"attach_private_data::initialize_from_string");
+	}
 };
 } // namespace attach
 } // namespace bpftime

attach/base_attach_impl/attach_private_data.hpp

@@ -10,8 +10,10 @@ namespace bpftime
 namespace attach
 {
 using override_return_set_callback = std::function<void(uint64_t, uint64_t)>;
+
 // Used by filter to record the return value
-extern thread_local std::optional<override_return_set_callback>
+// Use inline thread_local to ensure ODR
+inline thread_local std::optional<override_return_set_callback>
 	curr_thread_override_return_callback;
 
 // A wrapper function for an entry function of an ebpf program
@@ -23,6 +25,7 @@ class base_attach_impl {
     public:
 	// Detach a certain attach entry by a local attach id
 	virtual int detach_by_id(int id) = 0;
+
 	// Create an attach entry with an ebpf callback. To avoid messing up the
 	// code base, we don't use bpftime_prog here, instead, we require a
 	// callback accept the same argument as bpftime_prog::run The callback
@@ -31,14 +34,54 @@ class base_attach_impl {
 	virtual int create_attach_with_ebpf_callback(
 		ebpf_run_callback &&cb, const attach_private_data &private_data,
 		int attach_type) = 0;
+
 	// Allocate a new attach entry id
-	int allocate_id();
-	virtual ~base_attach_impl();
+	int allocate_id()
+	{
+		return next_id++;
+	}
+
+	virtual ~base_attach_impl(){};
 
     private:
 	int next_id = 1;
 };
 } // namespace attach
 } // namespace bpftime
 
+// The use of extern "C" allows the function to be called from C code
+extern "C" {
+
+// Set the return value of the current context
+inline uint64_t bpftime_set_retval(uint64_t value)
+{
+	using namespace bpftime::attach;
+	if (curr_thread_override_return_callback.has_value()) {
+		curr_thread_override_return_callback.value()(0, value);
+	} else {
+		spdlog::error(
+			"Called bpftime_set_retval, but no retval callback was set");
+		assert(false);
+	}
+	return 0;
+}
+
+// Override the return value of the current context
+inline uint64_t bpftime_override_return(uint64_t ctx, uint64_t value)
+{
+	using namespace bpftime::attach;
+	if (curr_thread_override_return_callback.has_value()) {
+		spdlog::debug("Overriding return value for ctx {:x} with {}",
+			      ctx, value);
+		curr_thread_override_return_callback.value()(ctx, value);
+	} else {
+		spdlog::error(
+			"Called bpftime_override_return, but no retval callback was set");
+		assert(false);
+	}
+	return 0;
+}
+
+} // extern "C"
+
 #endif