initial commit of libbt

7 files changed, 312 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3c27884
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+libbt.so
+out/
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..bd97388
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,19 @@
+all: $(patsubst example/%.c, out/%, $(wildcard example/*.c))
+all: $(patsubst example/%.c, run/%, $(wildcard example/*.c))
+
+CFLAGS := -Wall -Wextra -g -O2
+CFLAGS_recurse2 := -lpthread
+
+run/%:
+	LD_PRELOAD=$(PWD)/libbt.so out/$* || test $$? -eq 42 && exit 0
+
+out/%: example/%.c libbt.so
+	@mkdir -p out
+	$(CC) -o $@ $< -rdynamic $(FLAGS) $(CFLAGS_$*)
+
+libbt.so: bt.c
+	$(CC) -o $@ $^ -shared -fPIC -static-libgcc -ldl $(FLAGS)
+
+clean:
+	$(RM) -r out
+	$(RM) libbt.so
diff --git a/bt.c b/bt.c
new file mode 100644
index 0000000..4a2c743
--- /dev/null
+++ b/bt.c
@@ -0,0 +1,206 @@
+/**
+ * MIT License
+ *
+ * Copyright (c) 2024 Johannes Stölp
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ **/
+
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <signal.h>
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <unwind.h>  // from gcc, clang
+
+#define LOG(fmt, ...)                                              \
+  do {                                                             \
+    char buf[1024];                                                \
+    int cnt = snprintf(buf, sizeof(buf), fmt "\n", ##__VA_ARGS__); \
+    write(STDERR_FILENO, buf, cnt);                                \
+  } while (0)
+
+#define INFO(fmt, ...) LOG("[\e[0;32mINFO:BT\e[0m]: " fmt, ##__VA_ARGS__)
+#define WARN(fmt, ...) LOG("[\e[0;33mWARN:BT\e[0m]: " fmt, ##__VA_ARGS__)
+#define FAIL(fmt, ...) LOG("[\e[0;31mFAIL:BT\e[0m]: " fmt, ##__VA_ARGS__)
+
+// -- UNWIND HANDLER -----------------------------------------------------------
+
+struct unwind_data {
+  int num_frames;
+  int frame;
+  int skip;
+};
+
+static _Unwind_Reason_Code libbt_handle_unwind_frame(
+    struct _Unwind_Context* uctx,
+    void* arg) {
+  struct unwind_data* data = (struct unwind_data*)arg;
+  void* pc                 = (void*)_Unwind_GetIP(uctx);
+
+  if (pc == NULL) {
+    return _URC_END_OF_STACK;
+  }
+
+  if (data->skip > 0) {
+    data->skip -= 1;
+    return _URC_NO_REASON;
+  }
+
+  Dl_info info;
+  memset(&info, 0, sizeof(info));
+  if (dladdr(pc, &info) == 0) {
+    FAIL("dladdr call failed pc=%p stop unwinding", pc);
+    return _URC_END_OF_STACK;
+  }
+
+  if (info.dli_saddr) {
+    LOG("#%2d [%16p] %s+0x%lx %s+0x%lx", data->frame, pc, info.dli_sname,
+        pc - info.dli_saddr, info.dli_fname, info.dli_saddr - info.dli_fbase);
+  } else {
+    LOG("#%2d [%16p] %s+0x%lx", data->frame, pc, info.dli_fname,
+        pc - info.dli_fbase);
+  }
+
+  if (data->frame++ < data->num_frames) {
+    return _URC_NO_REASON;
+  }
+  return _URC_END_OF_STACK;
+}
+
+// -- SIGNAL HANDLING ----------------------------------------------------------
+
+static struct sigaction OLD;
+static struct sigaction NEW;
+
+static void libbt_report(int sig, siginfo_t* info, void* ucontext) {
+  INFO("caught signal %d", sig);
+
+  struct unwind_data ctx = {
+      .num_frames = 10,
+      .frame      = 0,
+      .skip       = 2,
+  };
+  _Unwind_Backtrace(libbt_handle_unwind_frame, &ctx);
+
+  if (OLD.sa_flags & SA_SIGINFO && OLD.sa_sigaction) {
+    OLD.sa_sigaction(sig, info, ucontext);
+  } else if (OLD.sa_handler) {
+    OLD.sa_handler(sig);
+  }
+
+  const char* noexit = getenv("BT_NOEXIT");
+  if (noexit && noexit[0] == '1') {
+    return;
+  }
+  INFO("exit after catching signal, set BT_NOEXIT=1 to keep running");
+  exit(42);
+}
+
+static void* libbt_install_sigstack() {
+  const size_t STACK_SIZE = 8192;
+
+  void* sp = malloc(STACK_SIZE);
+  if (sp == NULL) {
+    WARN("failed to allocate alternative signal stack");
+    return NULL;
+  }
+
+  stack_t stack = {
+      .ss_sp    = sp,
+      .ss_flags = 0,
+      .ss_size  = STACK_SIZE,
+  };
+  if (sigaltstack(&stack, NULL) != 0) {
+    WARN("failed to setup alternative signal stack");
+  }
+  return sp;
+}
+
+static int libbt_install_sighandler() {
+  memset(&OLD, 0, sizeof(OLD));
+  memset(&NEW, 0, sizeof(NEW));
+
+  NEW.sa_flags     = SA_SIGINFO | SA_ONSTACK;
+  NEW.sa_sigaction = libbt_report;
+
+  return sigaction(SIGSEGV, &NEW, &OLD);
+}
+
+// -- THREAD HANDLING ----------------------------------------------------------
+
+int (*NEXT_PTHREAD_CREATE)(pthread_t*,
+                           const pthread_attr_t*,
+                           void* (*)(void*),
+                           void*);
+
+static int THREAD_CREATE_SIGSTACK = 0;
+
+struct thread_arg {
+  void* (*start_routine)(void*);
+  void* restrict arg;
+};
+
+static void* thread_entry(void* th_arg) {
+  struct thread_arg arg = *(struct thread_arg*)th_arg;
+  free(th_arg);
+
+  void* sp  = THREAD_CREATE_SIGSTACK ? libbt_install_sigstack() : NULL;
+  void* ret = arg.start_routine(arg.arg);
+  free(sp);
+  return ret;
+}
+
+int pthread_create(pthread_t* thread,
+                   const pthread_attr_t* attr,
+                   void* (*start_routine)(void*),
+                   void* arg) {
+  assert(NEXT_PTHREAD_CREATE);
+
+  struct thread_arg* th_arg = malloc(sizeof(struct thread_arg));
+  th_arg->start_routine     = start_routine;
+  th_arg->arg               = arg;
+  return NEXT_PTHREAD_CREATE(thread, attr, thread_entry, th_arg);
+}
+
+// -- GLOBAL INITIALIZATION ----------------------------------------------------
+
+static void __attribute__((constructor)) init() {
+  NEXT_PTHREAD_CREATE = dlsym(RTLD_NEXT, "pthread_create");
+  if (NEXT_PTHREAD_CREATE == NULL) {
+    FAIL("failed to get pthread_create");
+    exit(1);
+  }
+
+  if (libbt_install_sighandler() != 0) {
+    FAIL("failed to install signal handler");
+    return;
+  }
+  INFO("installed signal handler");
+
+  // Install signal stack for main thread, and leak it leak.
+  libbt_install_sigstack();
+
+  // Only create signal stacks in threads if the signal handler was installed.
+  THREAD_CREATE_SIGSTACK = 1;
+}
diff --git a/example/raise1.c b/example/raise1.c
new file mode 100644
index 0000000..a0be4f5
--- /dev/null
+++ b/example/raise1.c
@@ -0,0 +1,17 @@
+#include <signal.h>
+
+// Raise from main thread.
+
+void foo() {
+  raise(SIGSEGV);
+}
+void bar() {
+  foo();
+}
+void qux() {
+  bar();
+}
+
+int main() {
+  qux();
+}
diff --git a/example/raise2.c b/example/raise2.c
new file mode 100644
index 0000000..056a341
--- /dev/null
+++ b/example/raise2.c
@@ -0,0 +1,25 @@
+#include <pthread.h>
+#include <signal.h>
+
+// Raise from different thread.
+
+void foo() {
+  raise(SIGSEGV);
+}
+void bar() {
+  foo();
+}
+void qux() {
+  bar();
+}
+
+void* thread(void*) {
+  qux();
+  return 0;
+}
+
+int main() {
+  pthread_t th;
+  pthread_create(&th, NULL, thread, NULL);
+  pthread_join(th, NULL);
+}
diff --git a/example/recurse1.c b/example/recurse1.c
new file mode 100644
index 0000000..e5a86bc
--- /dev/null
+++ b/example/recurse1.c
@@ -0,0 +1,17 @@
+// Stack overflow on main thread.
+
+void qux();
+
+void foo() {
+  qux();
+}
+void bar() {
+  foo();
+}
+void qux() {
+  bar();
+}
+
+int main() {
+  foo();
+}
diff --git a/example/recurse2.c b/example/recurse2.c
new file mode 100644
index 0000000..1fe1c4d
--- /dev/null
+++ b/example/recurse2.c
@@ -0,0 +1,26 @@
+#include <pthread.h>
+
+// Stack overflow on different thread.
+
+void qux();
+
+void foo() {
+  qux();
+}
+void bar() {
+  foo();
+}
+void qux() {
+  bar();
+}
+
+void* thread(void*) {
+  foo();
+  return 0;
+}
+
+int main() {
+  pthread_t th;
+  pthread_create(&th, NULL, thread, NULL);
+  pthread_join(th, NULL);
+}