cmake: add support for libbacktrace, fix two build issues

Also:
- memdebug: fix symbol collision in unity builds.
- memdebug: fix compiler warning by making a variable static.

Follow-up to c77bed81a2 #19657

Closes #19666

.github/scripts/pyspelling.words

@@ -434,6 +434,7 @@ LDAPS
 ldaps
 LF
 LGTM
+libbacktrace
 libbrotlidec
 libc
 libcurl

CMake/FindLibbacktrace.cmake

@@ -0,0 +1,52 @@
+#***************************************************************************
+#                                  _   _ ____  _
+#  Project                     ___| | | |  _ \| |
+#                             / __| | | | |_) | |
+#                            | (__| |_| |  _ <| |___
+#                             \___|\___/|_| \_\_____|
+#
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at https://curl.se/docs/copyright.html.
+#
+# You may opt to use, copy, modify, merge, publish, distribute and/or sell
+# copies of the Software, and permit persons to whom the Software is
+# furnished to do so, under the terms of the COPYING file.
+#
+# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+# KIND, either express or implied.
+#
+# SPDX-License-Identifier: curl
+#
+###########################################################################
+# Find the libbacktrace library
+#
+# Input variables:
+#
+# - `LIBBACKTRACE_INCLUDE_DIR`:   Absolute path to libbacktrace include directory.
+# - `LIBBACKTRACE_LIBRARY`:       Absolute path to `libbacktrace` library.
+#
+# Result variables:
+#
+# - `LIBBACKTRACE_FOUND`:         System has libbacktrace.
+# - `LIBBACKTRACE_INCLUDE_DIRS`:  The libbacktrace include directories.
+# - `LIBBACKTRACE_LIBRARIES`:     The libbacktrace library names.
+
+find_path(LIBBACKTRACE_INCLUDE_DIR NAMES "backtrace.h")
+find_library(LIBBACKTRACE_LIBRARY NAMES "backtrace" "libbacktrace")
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Libbacktrace
+  REQUIRED_VARS
+    LIBBACKTRACE_INCLUDE_DIR
+    LIBBACKTRACE_LIBRARY
+)
+
+if(LIBBACKTRACE_FOUND)
+  set(LIBBACKTRACE_INCLUDE_DIRS ${LIBBACKTRACE_INCLUDE_DIR})
+  set(LIBBACKTRACE_LIBRARIES    ${LIBBACKTRACE_LIBRARY})
+endif()
+
+mark_as_advanced(LIBBACKTRACE_INCLUDE_DIR LIBBACKTRACE_LIBRARY)

CMakeLists.txt

@@ -1421,6 +1421,21 @@ if(CURL_USE_GSSAPI)
   endif()
 endif()
 
+# libbacktrace
+option(CURL_USE_LIBBACKTRACE "Use libbacktrace. Requires build with TrackMemory and DWARF debug information." OFF)
+if(CURL_USE_LIBBACKTRACE)
+  if(NOT ENABLE_CURLDEBUG)
+    message(FATAL_ERROR "libbacktrace requires TrackMemory enabled")
+  endif()
+  if(NOT CMAKE_BUILD_TYPE MATCHES "(Debug|RelWithDebInfo)")
+    message(FATAL_ERROR "libbacktrace requires debug information")
+  endif()
+  find_package(Libbacktrace REQUIRED)
+  list(APPEND CURL_LIBS ${LIBBACKTRACE_LIBRARIES})
+  include_directories(SYSTEM ${LIBBACKTRACE_INCLUDE_DIRS})
+  set(USE_BACKTRACE ON)
+endif()
+
 # libuv
 option(CURL_USE_LIBUV "Use libuv for event-based tests" OFF)
 if(CURL_USE_LIBUV)

Makefile.am

@@ -37,6 +37,7 @@ CMAKE_DIST =                                    \
  CMake/FindGnuTLS.cmake                         \
  CMake/FindGSS.cmake                            \
  CMake/FindLDAP.cmake                           \
+ CMake/FindLibbacktrace.cmake                   \
  CMake/FindLibgsasl.cmake                       \
  CMake/FindLibidn2.cmake                        \
  CMake/FindLibpsl.cmake                         \

docs/INSTALL-CMAKE.md

@@ -355,6 +355,7 @@ Details via CMake
 - `CURL_USE_GNUTLS`:                        Enable GnuTLS for SSL/TLS. Default: `OFF`
 - `CURL_USE_GSASL`:                         Use libgsasl. Default: `OFF`
 - `CURL_USE_GSSAPI`:                        Use GSSAPI implementation. Default: `OFF`
+- `CURL_USE_LIBBACKTRACE`:                  Use [libbacktrace](https://github.com/ianlancetaylor/libbacktrace). Requires build with TrackMemory and DWARF debug information. Default: `OFF`
 - `CURL_USE_LIBPSL`:                        Use libpsl. Default: `ON`
 - `CURL_USE_LIBSSH2`:                       Use libssh2. Default: `ON`
 - `CURL_USE_LIBSSH`:                        Use libssh. Default: `OFF`
@@ -411,6 +412,8 @@ Details via CMake
 - `LDAP_INCLUDE_DIR`:                       Absolute path to LDAP include directory.
 - `LDAP_LIBRARY`:                           Absolute path to `ldap` library.
 - `LDAP_LBER_LIBRARY`:                      Absolute path to `lber` library.
+- `LIBBACKTRACE_INCLUDE_DIR`:               Absolute path to libbacktrace include directory (https://github.com/ianlancetaylor/libbacktrace).
+- `LIBBACKTRACE_LIBRARY`:                   Absolute path to `libbacktrace` library.
 - `LIBGSASL_INCLUDE_DIR`:                   Absolute path to libgsasl include directory.
 - `LIBGSASL_LIBRARY`:                       Absolute path to `libgsasl` library.
 - `LIBIDN2_INCLUDE_DIR`:                    Absolute path to libidn2 include directory.

lib/curl_config.h.cmake

@@ -730,6 +730,9 @@ ${SIZEOF_TIME_T_CODE}
 /* Define to 1 if you have the <uv.h> header file. */
 #cmakedefine HAVE_UV_H 1
 
+/* if libbacktrace is in use */
+#cmakedefine USE_BACKTRACE 1
+
 /* Define to 1 if you do not want the OpenSSL configuration to be loaded
    automatically */
 #cmakedefine CURL_DISABLE_OPENSSL_AUTO_LOAD_CONFIG 1

lib/memdebug.c

@@ -63,7 +63,7 @@ static bool registered_cleanup = FALSE; /* atexit registered cleanup */
 static bool memlimit = FALSE; /* enable memory limit */
 static long memsize = 0;  /* set number of mallocs allowed */
 #ifdef USE_BACKTRACE
-struct backtrace_state *btstate;
+static struct backtrace_state *btstate;
 #endif
 
 /* LeakSantizier (LSAN) calls _exit() instead of exit() when a leak is detected
@@ -81,7 +81,8 @@ static void curl_dbg_cleanup(void)
   curl_dbg_logfile = NULL;
 }
 #ifdef USE_BACKTRACE
-static void error_callback(void *data, const char *message, int error_number)
+static void error_bt_callback(void *data, const char *message,
+                              int error_number)
 {
   (void)data;
   if(error_number == -1)
@@ -102,7 +103,7 @@ static int full_callback(void *data, uintptr_t pc, const char *pathname,
 
 static void dump_bt(void)
 {
-  backtrace_full(btstate, 0, full_callback, error_callback, NULL);
+  backtrace_full(btstate, 0, full_callback, error_bt_callback, NULL);
 }
 #else
 #define dump_bt() /* nothing to do */
@@ -123,7 +124,7 @@ void curl_dbg_memdebug(const char *logname)
 #endif
   }
 #ifdef USE_BACKTRACE
-  btstate = backtrace_create_state(NULL, 0, error_callback, NULL);
+  btstate = backtrace_create_state(NULL, 0, error_bt_callback, NULL);
 #endif
   if(!registered_cleanup)
     registered_cleanup = !atexit(curl_dbg_cleanup);