For Linux GCC builds, print stack trace on crash.

ChangeLog

@@ -80,6 +80,7 @@
 60. Fix small side-bar when at top, or bottom.
 61. Try to make UI responseive to available width. Hide toolbar and statusbar
     items in insufficient space. Switch view type when narrow.
+62. For Linux GCC builds, print stack trace on crash.
 
 2.2.0
 -----

gui/main.cpp

@@ -255,8 +255,89 @@ static void installDebugMessageHandler(const QString &cmdLine)
     qInstallMessageHandler(cantataQtMsgHandler);
 }
 
+#if defined Q_OS_LINUX && defined __GNUC__
+#include <execinfo.h>
+#include <unistd.h>
+#include <signal.h>
+#include <cxxabi.h>
+
+static void sigHandler(int i)
+{
+    // Adapted from: https://panthema.net/2008/0901-stacktrace-demangled/
+
+    // stacktrace.h (c) 2008, Timo Bingmann from http://idlebox.net/
+    // published under the WTFPL v2.0
+    static const int constMaxFuncNameLen = 256;
+    static const int constNumLevels = 15;
+    void *addrlist[constNumLevels+1];
+
+    fprintf(stderr, "Unfortunately Cantata has crashed. Please report a bug at \n"
+                    "https://github.com/CDrummond/cantata/issues/ and include the following stack trace:\n\n");
+    // retrieve current stack addresses
+    int addrlen = backtrace(addrlist, sizeof(addrlist) / sizeof(void*));
+    if (!addrlen) {
+        fprintf(stderr, "Failed to produce stack trace!\n");
+        _exit(0);
+    }
+
+    char ** symbolList = backtrace_symbols(addrlist, addrlen);
+    char funcName[constMaxFuncNameLen];
+
+    // iterate over the returned symbol lines. skip the first, it is the
+    // address of this function.
+    for (int i = 1; i < addrlen; i++) {
+        char *beginName = nullptr;
+        char *beginOffset = nullptr;
+        char *endOffset = nullptr;
+
+        // find parentheses and +address offset surrounding the mangled name:
+        // ./module(function+0x15c) [0x8048a6d]
+        for (char *p = symbolList[i]; *p; ++p) {
+            if (*p == '(') {
+                beginName = p;
+            } else if (*p == '+') {
+                beginOffset = p;
+            } else if (*p == ')' && beginOffset) {
+                endOffset = p;
+                break;
+            }
+        }
+
+        if (beginName && beginOffset && endOffset && beginName < beginOffset) {
+            *beginName++ = '\0';
+            *beginOffset++ = '\0';
+            *endOffset = '\0';
+
+            // mangled name is now in [begin_name, begin_offset) and caller
+            // offset in [begin_offset, end_offset). now apply
+            // __cxa_demangle():
+
+            int status = 0;
+            size_t nameLen = constMaxFuncNameLen;
+            char * ret = abi::__cxa_demangle(beginName, funcName, &nameLen, &status);
+            if (!status) {
+                fprintf(stderr, "  %s : %s+%s\n", symbolList[i], ret, beginOffset);
+            } else {
+                // demangling failed. Output function name as a C function with
+                // no arguments.
+                fprintf(stderr, "  %s : %s()+%s\n", symbolList[i], beginName, beginOffset);
+            }
+        } else {
+            // couldn't parse the line? print the whole line.
+            fprintf(stderr, "  %s\n", symbolList[i]);
+        }
+    }
+
+    free(symbolList);
+    _exit(1);
+}
+#endif
+
 int main(int argc, char *argv[])
 {
+    #if defined Q_OS_LINUX && defined __GNUC__
+    signal(SIGSEGV, sigHandler);
+    #endif
     QThread::currentThread()->setObjectName("GUI");
     QCoreApplication::setApplicationName(PACKAGE_NAME);
     QCoreApplication::setOrganizationName(ORGANIZATION_NAME);