print_trace

Makefile

@@ -4,6 +4,7 @@ CFLAGS = -Wall
 PROG = helloworld
 HPTEST = hptest
 USTACK = userstack
+SPID = stack-pid
 
 UDIR = $(PWD)/source/uapi
 MDIR := $(PWD)/source
@@ -18,7 +19,7 @@ OUTPUT_DIR = $(PWD)/build
 # obj-m := kernel/$(KMOD).o
 # $(KMOD)-objs := kernel/monitor_kernel.o
 
-all: $(PROG) $(HPTEST) $(USTACK) module
+all: $(PROG) $(HPTEST) $(USTACK) $(SPID) module
 
 $(PROG): $(TDIR)/helloworld.c
 	mkdir -p $(OUTPUT_DIR)
@@ -30,7 +31,11 @@ $(HPTEST): $(TDIR)/hptest.c
 
 $(USTACK): $(TDIR)/userstack.c
 	mkdir -p $(OUTPUT_DIR)
-	$(CC) $(CFLAGS) -o $(OUTPUT_DIR)/$(USTACK) $(TDIR)/userstack.c
+	$(CC) -g $(CFLAGS) -o $(OUTPUT_DIR)/$(USTACK) $(TDIR)/userstack.c -lunwind -lunwind-x86_64
+
+$(SPID): $(TDIR)/stack-pid.c
+	mkdir -p $(OUTPUT_DIR)
+	$(CC) $(CFLAGS) -o $(OUTPUT_DIR)/$(SPID) $(TDIR)/stack-pid.c -lunwind -lunwind-x86_64 -lunwind-ptrace
 
 module:
 	make -C $(KDIR) M=$(MDIR) modules

testcase/backtrace.c

@@ -0,0 +1,52 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <execinfo.h>
+#include <elfutils/libdwfl.h>
+
+#define MAX_STACK_FRAMES 64
+static void *stack_traces[MAX_STACK_FRAMES];
+
+void print_trace() {
+  int stack_depth = backtrace(stack_traces, MAX_STACK_FRAMES);
+  Dwfl_Callbacks callbacks = {
+    .find_elf = dwfl_linux_proc_find_elf,
+    .find_debuginfo = dwfl_standard_find_debuginfo,
+    .debuginfo_path = NULL
+  };
+
+  Dwfl *dwfl = dwfl_begin(&callbacks);
+  dwfl_linux_proc_report(dwfl, getpid());
+  dwfl_report_end(dwfl, NULL, NULL);
+
+  for (int i = 0; i < stack_depth; ++i) {
+    const char *modname;
+    const char *symname;
+    GElf_Off offset;
+    Dwfl_Module *mod = dwfl_addrmodule(dwfl, (uintptr_t)stack_traces[i]);
+    Dwfl_Line *line = dwfl_module_getsrc(mod, (uintptr_t)stack_traces[i]);
+    const char *src;
+    int lineno, colno;
+
+    if (line) {
+      src = dwfl_lineinfo(mod, line, &lineno, &colno, &modname, &symname);
+      printf("%s (%d) %s\n", src, lineno, symname);
+    }
+  }
+
+  dwfl_end(dwfl);
+}
+
+void foo() {
+  print_trace();
+}
+
+void bar() {
+  foo();
+}
+
+int main(int argc, char **argv) {
+  bar();
+  return 0;
+}

testcase/stack-pid.c

@@ -0,0 +1,54 @@
+#include <sys/ptrace.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <stdarg.h>
+
+#include <libunwind-ptrace.h>
+
+void die(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	exit(1);
+}
+
+
+int main(int argc, char **argv)
+{
+	if (argc != 2)
+		die("USAGE: unwind-pid <pid>\n");
+
+	unw_addr_space_t as = unw_create_addr_space(&_UPT_accessors, 0);
+
+	pid_t pid = atoi(argv[1]);
+	if (ptrace(PTRACE_ATTACH, pid, 0, 0) != 0)
+		die("ERROR: cannot attach to %d\n", pid);
+
+	void *context = _UPT_create(pid);
+	unw_cursor_t cursor;
+	if (unw_init_remote(&cursor, as, context) != 0)
+		die("ERROR: cannot initialize cursor for remote unwinding\n");
+
+	do {
+		unw_word_t offset, pc;
+		char sym[4096];
+		if (unw_get_reg(&cursor, UNW_REG_IP, &pc))
+			die("ERROR: cannot read program counter\n");
+
+		printf("0x%lx: ", pc);
+
+		if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0)
+			printf("(%s+0x%lx)\n", sym, offset);
+		else
+			printf("-- no symbol name found\n");
+	} while (unw_step(&cursor) > 0);
+
+	_UPT_destroy(context);
+	(void) ptrace(PTRACE_DETACH, pid, 0, 0);
+
+	return 0;
+}

testcase/userstack.c

@@ -1,15 +1,46 @@
 #include <stdio.h>
+#include <libunwind.h>
 #include <unistd.h>
 
 void customFunction1(int n);
 void customFunction2(int n);
 void customFunction3(int n);
 
+// Call this function to get a backtrace.
+void backtrace() {
+  unw_cursor_t cursor;
+  unw_context_t context;
+
+  // Initialize cursor to current frame for local unwinding.
+  unw_getcontext(&context);
+  unw_init_local(&cursor, &context);
+
+  // Unwind frames one by one, going up the frame stack.
+  while (unw_step(&cursor) > 0) {
+    unw_word_t offset, pc;
+    unw_get_reg(&cursor, UNW_REG_IP, &pc);
+    if (pc == 0) {
+      break;
+    }
+    printf("0x%lx:", pc);
+
+    char sym[256];
+    if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0) {
+      printf(" (%s+0x%lx)\n", sym, offset);
+    } else {
+      printf(" -- error: unable to obtain symbol name for this frame\n");
+    }
+  }
+}
+
 void customFunction1(int n) {
     if(n <= 0) {
         printf("End of recursion\n");
+        // output backtrace
+        printf("pid: %d\n", getpid());
+        backtrace();
         while (1) {
-            // sleep(1);
+            sleep(1);
         } // never return, keep stack
         return;
     } else {