diff options
Diffstat (limited to 'bt.c')
| -rw-r--r-- | bt.c | 206 |
1 files changed, 206 insertions, 0 deletions
@@ -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; +} |