split out backtracing and symbol lookup

add support for backtracing other threads

stepmania/src/archutils/Unix/Backtrace.h

@@ -0,0 +1,35 @@
+#ifndef BACKTRACE_H
+#define BACKTRACE_H
+
+/* This API works like backtrace_pointers(), to retrieve a stack trace. */
+
+/* This contains the information necessary to backtrace a thread. */
+struct BacktraceContext
+{
+#if defined(LINUX)
+	long eip, esp, ebp;
+	pid_t pid;
+#endif
+};
+
+/* Initialize.  This is optional.  If not called explicitly, it will be
+ * called as necessary.  This may do things that are not safe to do in
+ * crash conditions. */
+void InitializeBacktrace();
+
+/* Retrieve up to size-1 backtrace pointers in buf.  The array will be
+ * null-terminated.  If ctx is NULL, retrieve the current backtrace; otherwise
+ * retrieve a backtrace for the given context.  (Not all backtracers may
+ * support contexts.) */
+void GetBacktrace( const void **buf, size_t size, BacktraceContext *ctx = NULL );
+
+/* Set up a BacktraceContext to get a backtrace for a thread.  ThreadID may
+ * be the current thread. */
+int GetThreadBacktraceContext( int ThreadID, BacktraceContext *ctx );
+void GetCurrentBacktraceContext( BacktraceContext *ctx );
+
+#define BACKTRACE_METHOD_NOT_AVAILABLE ((void*) -1)
+#define BACKTRACE_SIGNAL_TRAMPOLINE ((void*) -2)
+
+#endif
+