libc: add backtrace() functions

libc/backtrace.c

@@ -0,0 +1,116 @@
+/* Copyright (C) 2025 John Törnblom
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; see the file COPYING. If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include <dlfcn.h>
+#include <execinfo.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+
+#define MAX_SYMBOL_SIZE 99
+
+
+size_t
+backtrace(void **buffer, size_t size) {
+  void **frame = __builtin_frame_address(0);
+  void *addr = __builtin_return_address(0);
+  int i;
+
+  for(i=0; i<size && frame; i++) {
+    buffer[i] = addr;
+    frame = (void**)*frame;
+
+    if(frame) {
+      addr = *(frame+1);
+    } else {
+      break;
+    }
+  }
+
+  return i;
+}
+
+
+char**
+backtrace_symbols(void *const *buffer, size_t size) {
+  void* mem = malloc(size*sizeof(char*) + size*MAX_SYMBOL_SIZE);
+  char *strbuf = mem + (size*sizeof(char*));
+  char **symbols = mem;
+  Dl_info dli;
+
+  if(!mem) {
+    return NULL;
+  }
+
+  for(int i=0; i<size; i++) {
+    void* addr = buffer[i];
+    symbols[i] = strbuf + (i*MAX_SYMBOL_SIZE);
+
+    if(!dladdr(addr, &dli)) {
+      snprintf(symbols[i], MAX_SYMBOL_SIZE, "? [0x%p]", addr);
+
+    } else if(!dli.dli_sname) {
+      snprintf(symbols[i], MAX_SYMBOL_SIZE, "%s(+0x%p) [0x%p]",
+               dli.dli_fname,
+               (void*)(addr - dli.dli_fbase),
+               addr);
+
+    } else {
+      snprintf(symbols[i], MAX_SYMBOL_SIZE, "%s(%s+0x%p) [0x%p]",
+               dli.dli_fname,
+               dli.dli_sname,
+               (void*)(addr - dli.dli_fbase),
+               addr);
+    }
+  }
+
+  return (char**)mem;
+}
+
+
+int
+backtrace_symbols_fd(void *const* buffer, size_t size, int fd) {
+  char sym[MAX_SYMBOL_SIZE+1];
+  Dl_info dli;
+
+  for(int i=0; i<size; i++) {
+    void* addr = buffer[i];
+
+    if(!dladdr(addr, &dli)) {
+      snprintf(sym, MAX_SYMBOL_SIZE, "? [0x%p]\n", addr);
+
+    } else if(!dli.dli_sname) {
+      snprintf(sym, MAX_SYMBOL_SIZE, "%s(+0x%p) [0x%p]\n",
+               dli.dli_fname,
+               (void*)(addr - dli.dli_fbase),
+               addr);
+
+    } else {
+      snprintf(sym, MAX_SYMBOL_SIZE, "%s(%s+0x%p) [0x%p]\n",
+               dli.dli_fname,
+               dli.dli_sname,
+               (void*)(addr - dli.dli_fbase),
+               addr);
+    }
+    if(write(fd, sym, strlen(sym)) != strlen(sym)) {
+      return -1;
+    }
+  }
+
+  return 0;
+}