[LPC2025] snooper: bpf_task_work_schedule() and file-based dynptr example

examples/c/.gitignore

@@ -16,3 +16,7 @@
 /lsm
 /cmake-build-debug/
 /cmake-build-release/
+compile_commands.json
+/app
+/libapp.so
+/snooper

examples/c/CMakeLists.txt

@@ -77,6 +77,7 @@ find_package(BpfObject REQUIRED)
 file(GLOB apps *.bpf.c)
 if(NOT CARGO_EXISTS)
   list(REMOVE_ITEM apps ${CMAKE_CURRENT_SOURCE_DIR}/profile.bpf.c)
+  list(REMOVE_ITEM apps ${CMAKE_CURRENT_SOURCE_DIR}/snooper.bpf.c)
 endif()
 foreach(app ${apps})
   get_filename_component(app_stem ${app} NAME_WE)
@@ -93,4 +94,10 @@ foreach(app ${apps})
     target_link_libraries(${app_stem}
       ${CMAKE_CURRENT_SOURCE_DIR}/../../blazesym/target/release/libblazesym_c.a -lpthread -lrt -ldl)
   endif()
+  if(${app_stem} STREQUAL snooper)
+    target_include_directories(${app_stem} PRIVATE
+      ${CMAKE_CURRENT_SOURCE_DIR}/../../blazesym/capi/include)
+    target_link_libraries(${app_stem}
+      ${CMAKE_CURRENT_SOURCE_DIR}/../../blazesym/target/release/libblazesym_c.a -lpthread -lrt -ldl)
+  endif()
 endforeach()

examples/c/Makefile

@@ -31,7 +31,7 @@ CARGO ?= $(shell which cargo)
 ifeq ($(strip $(CARGO)),)
 BZS_APPS :=
 else
-BZS_APPS := profile
+BZS_APPS := profile snooper
 APPS += $(BZS_APPS)
 # Required by libblazesym
 ALL_LDFLAGS += -lrt -ldl -lpthread -lm
@@ -70,12 +70,12 @@ $(call allow-override,CC,$(CROSS_COMPILE)cc)
 $(call allow-override,LD,$(CROSS_COMPILE)ld)
 
 .PHONY: all
-all: $(APPS)
+all: $(APPS) app
 
 .PHONY: clean
 clean:
 	$(call msg,CLEAN)
-	$(Q)rm -rf $(OUTPUT) $(APPS)
+	$(Q)rm -rf $(OUTPUT) $(APPS) app libapp.so
 
 $(OUTPUT) $(OUTPUT)/libbpf $(BPFTOOL_OUTPUT):
 	$(call msg,MKDIR,$@)
@@ -136,3 +136,12 @@ $(APPS): %: $(OUTPUT)/%.o $(LIBBPF_OBJ) | $(OUTPUT)
 
 # keep intermediate (.skel.h, .bpf.o, etc) targets
 .SECONDARY:
+
+# Build target app and its shared library
+libapp.so: app_lib.c app_lib.h
+	$(call msg,SHLIB,$@)
+	$(Q)$(CC) $(CFLAGS) -shared -fPIC -o $@ app_lib.c
+
+app: app.c app_lib.h libapp.so
+	$(call msg,BINARY,$@)
+	$(Q)$(CC) $(CFLAGS) -o $@ app.c -L. -lapp -Wl,-rpath,'$$ORIGIN' -lpthread

examples/c/app.c

@@ -0,0 +1,140 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <dlfcn.h>
+#include <elf.h>
+#include <pthread.h>
+#include "app_lib.h"
+
+static __thread int tls_dont_care; /* just to avoid zero offsets everywhere else */
+
+__thread int tls_exec;
+extern __thread int tls_shared;
+
+static __thread int tls_local_exec;
+
+int __attribute__((weak)) get_tls_exec(void)
+{
+	return tls_exec;
+}
+
+int __attribute__((weak)) get_tls_shared(void)
+{
+	return tls_shared;
+}
+
+int __attribute__((weak)) get_tls_local_exec(void)
+{
+	return tls_local_exec;
+}
+
+/* Forward declarations for recursive functions */
+void func_a(int depth);
+void func_b(int depth);
+void func_c(int depth);
+
+static __always_inline void func_mux(int depth)
+{
+	if (depth <= 0)
+		return;
+
+	switch (rand() % 3) {
+	case 0: func_a(depth - 1); break;
+	case 1: func_b(depth - 1); break;
+	case 2: func_c(depth - 1); break;
+	}
+}
+
+void func_a(int depth)
+{
+	volatile char stack_space[120];
+	stack_space[119] = 'a';
+	stack_space[0] += 1;
+
+	if (depth <= 0)
+		return;
+
+	func_mux(depth - 1);
+}
+
+void func_b(int depth)
+{
+	volatile char stack_space[350];
+	stack_space[349] = 'b';
+	stack_space[0] += 1;
+
+	if (depth <= 0)
+		return;
+
+	func_mux(depth - 1);
+}
+
+void func_c(int depth)
+{
+	volatile char stack_space[800];
+	stack_space[799] = 'c';
+	stack_space[0] += 1;
+
+	if (depth <= 0)
+		return;
+
+	func_mux(depth - 1);
+}
+
+static void *thread_func(void *arg)
+{
+	time_t last_print = 0;
+	(void)arg;
+
+	pthread_setname_np(pthread_self(), "app_thread");
+
+	while (1) {
+		time_t now;
+
+		errno = 123456789;
+		func_mux(10);
+		errno = 987654321;
+
+		now = time(NULL);
+		if (now > last_print) {
+			tls_exec += 4;
+			tls_shared += 8;
+			tls_local_exec += 16;
+			bump_tls_local_shared();
+			bump_tls_local_shared();
+
+			printf("Hello from thread (exec=%d, shared=%d, local_exec=%d, local_shared=%d)!\n",
+				get_tls_exec(), get_tls_shared(), get_tls_local_exec(), get_tls_local_shared());
+			last_print = now;
+		}
+	}
+
+	return NULL;
+}
+
+int main() {
+	pthread_t thread;
+
+	pthread_create(&thread, NULL, thread_func, NULL);
+
+	while (1) {
+		tls_dont_care += 1;
+		tls_exec += 2;
+		tls_shared += 4;
+		tls_local_exec += 8;
+		bump_tls_local_shared();
+
+		printf("Hello from app (exec=%d, shared=%d, local_exec=%d, local_shared=%d)!\n",
+			get_tls_exec(), get_tls_shared(), get_tls_local_exec(), get_tls_local_shared());
+		sleep(1);
+	}
+
+	return 0;
+}

examples/c/app_lib.c

@@ -0,0 +1,8 @@
+__thread int tls_shared;
+__thread int tls_shared2;
+static __thread int tls_local_shared;
+
+int get_tls_local_shared(void) { return tls_local_shared; }
+int get_tls_shared(void) { return tls_shared; }
+int get_tls_shared2(void) { return tls_shared2; }
+void bump_tls_local_shared(void) { tls_local_shared += 16; }

examples/c/app_lib.h

@@ -0,0 +1,7 @@
+#ifndef APP_LIB_H
+#define APP_LIB_H
+
+int get_tls_local_shared(void);
+void bump_tls_local_shared(void);
+
+#endif /* APP_LIB_H */