Fix GDB cannot work in release build

src/libos/Makefile

@@ -63,7 +63,7 @@ EDL_C_SRCS := $(addprefix $(BUILD_DIR)/src/libos/,src/Enclave_t.c src/Enclave_t.
 EDL_C_OBJS := $(addprefix $(BUILD_DIR)/src/libos/,src/Enclave_t.o)
 BUILTIN_C_SRCS := $(sort $(wildcard src/builtin/*.c))
 BUILTIN_C_OBJS := $(addprefix $(BUILD_DIR)/src/libos/,$(BUILTIN_C_SRCS:.c=.o))
-C_SRCS := $(filter-out $(BUILTIN_C_SRCS),$(sort $(wildcard src/*.c src/*/*.c)))
+C_SRCS := $(filter-out $(BUILTIN_C_SRCS),$(sort $(wildcard src/*.c src/*/*.c src/*/*/*.c)))
 C_OBJS := $(addprefix $(BUILD_DIR)/src/libos/,$(C_SRCS:.c=.o))
 CXX_SRCS := $(sort $(wildcard src/*.cpp src/*/*.cpp))
 CXX_OBJS := $(addprefix $(BUILD_DIR)/src/libos/,$(CXX_SRCS:.cpp=.o))
@@ -73,6 +73,8 @@ S_OBJS := $(addprefix $(BUILD_DIR)/src/libos/,$(S_SRCS:.S=.o))
 ALL_BUILD_SUBDIRS := $(sort $(patsubst %/,%,$(dir $(LIBOS_SO) $(EDL_C_OBJS) $(BUILTIN_C_OBJS) $(C_OBJS) $(CXX_OBJS) $(S_OBJS)) $(RUST_TARGET_DIR) $(RUST_OUT_DIR)))
 
 C_COMMON_FLAGS := -fno-stack-protector -I./include/
+# SGX GDB support
+C_COMMON_FLAGS += -g
 C_FLAGS := $(SGX_CFLAGS_T) $(C_COMMON_FLAGS)
 CXX_FLAGS := $(SGX_CXXFLAGS_T) $(C_COMMON_FLAGS)
 

src/libos/src/process/spawn/gdb_hook_load_elf.c

@@ -0,0 +1,21 @@
+#include <sys/types.h>
+
+/*
+ * Providing debug symbol information to GDB.
+ *
+ * This function is left empty deliberately and should NOT be removed.
+ *
+ * When SGX GDB is attached to the enclave, a break point will be inserted at the beginning
+ * of this function. So when this function is called at runtime, GDB can capture the arguments
+ * of this function, which gives the name of a loaded ELF file and the memory location where
+ * the ELF is loaded in the enclave. With this information, GDB can translate memory addresses
+ * to symbol names, thus give meaningful debug information.
+ *
+ * `__attribute__((optimize("O0")))` is used to prevent the compiler from optimizing this function in
+ * unexpected way (e.g., eliminating this empty function).
+ */
+void __attribute__((optimize("O0"))) occlum_gdb_hook_load_elf(
+    uint64_t elf_base,
+    const char* elf_path,
+    uint64_t elf_path_len) {
+}

src/libos/src/process/spawn/mod.rs

@@ -41,10 +41,6 @@ pub fn do_spawn_without_exec(
     Ok(new_tid)
 }
 
-// This function is used to provide information to debugger, so it is empty. Please do not remove it.
-#[no_mangle]
-pub extern "C" fn occlum_gdb_hook_load_elf(elf_base: u64, elf_path: &str, elf_path_len: usize) {}
-
 fn new_process(
     elf_path: &str,
     argv: &[CString],
@@ -70,9 +66,21 @@ fn new_process(
 
         // Notify debugger to load the symbols from elf file
         let ldso_elf_base = vm.get_elf_ranges()[1].start() as u64;
-        occlum_gdb_hook_load_elf(ldso_elf_base, ldso_path, ldso_path.len());
+        unsafe {
+            occlum_gdb_hook_load_elf(
+                ldso_elf_base,
+                ldso_path.as_ptr() as *const u8,
+                ldso_path.len() as u64,
+            );
+        }
         let exec_elf_base = vm.get_elf_ranges()[0].start() as u64;
-        occlum_gdb_hook_load_elf(exec_elf_base, elf_path, elf_path.len());
+        unsafe {
+            occlum_gdb_hook_load_elf(
+                exec_elf_base,
+                elf_path.as_ptr() as *const u8,
+                elf_path.len() as u64,
+            );
+        }
 
         let task = {
             let ldso_entry = {
@@ -227,4 +235,5 @@ fn parent_adopts_new_child(parent_ref: &ProcessRef, child_ref: &ProcessRef) {
 
 extern "C" {
     fn __occlum_syscall(num: i32, arg0: u64, arg1: u64, arg2: u64, arg3: u64, arg4: u64) -> i64;
+    fn occlum_gdb_hook_load_elf(elf_base: u64, elf_path: *const u8, elf_path_len: u64);
 }