os: use libunwind to generate backtraces

Libunwind generates backtraces much more reliably than glibc's "backtrace".

Before:
0: /opt/xserver/bin/X (0x400000+0x18ce36) [0x58ce36]
1: /opt/xserver/bin/X (xorg_backtrace+0x9) [0x58d119]
2: /opt/xserver/bin/X (0x400000+0x190d69) [0x590d69]
3: /lib64/libpthread.so.0 (0x7fb904268000+0x10a90) [0x7fb904278a90]
4: /lib64/libc.so.6 (ioctl+0x7) [0x7fb902fbf987]
5: /usr/lib64/libdrm.so.2 (drmIoctl+0x28) [0x7fb90405ffa8]
6: /usr/lib64/libdrm.so.2 (drmCommandWrite+0x1b) [0x7fb90406235b]
7: /usr/lib64/libdrm_nouveau.so.2 (nouveau_bo_wait+0x89) [0x7fb902009719]
8: /opt/xserver/lib/xorg/modules/drivers/nouveau_drv.so (0x7fb90220e000+0x76f3) [0x7fb9022156f3]
9: /opt/xserver/lib/xorg/modules/libexa.so (0x7fb9019c7000+0xbae0) [0x7fb9019d2ae0]
10: /opt/xserver/bin/X (0x400000+0x17d2b3) [0x57d2b3]
11: /opt/xserver/bin/X (0x400000+0xc9930) [0x4c9930]
12: /opt/xserver/bin/X (0x400000+0x3a81a) [0x43a81a]
13: /opt/xserver/bin/X (0x400000+0x3d6a1) [0x43d6a1]
14: /opt/xserver/bin/X (0x400000+0x2c2ca) [0x42c2ca]
15: /lib64/libc.so.6 (__libc_start_main+0xf5) [0x7fb902f019b5]
16: /opt/xserver/bin/X (0x400000+0x2c60d) [0x42c60d]
17: ?? [0x0]

After:
0: /opt/xserver/bin/X (OsSigHandler+0x39) [0x590d69]
1: /lib64/libpthread.so.0 (__restore_rt+0x0) [0x7fb904278a8f]
2: /lib64/libc.so.6 (ioctl+0x7) [0x7fb902fbf987]
3: /usr/lib64/libdrm.so.2 (drmIoctl+0x28) [0x7fb90405ffa8]
4: /usr/lib64/libdrm.so.2 (drmCommandWrite+0x1b) [0x7fb90406235b]
5: /usr/lib64/libdrm_nouveau.so.2 (nouveau_bo_wait+0x89) [0x7fb902009719]
6: /opt/xserver/lib/xorg/modules/drivers/nouveau_drv.so (nouveau_exa_download_from_screen+0x1a3) [0x7fb9022156f3]
7: /opt/xserver/lib/xorg/modules/libexa.so (exaGetImage+0x1f0) [0x7fb9019d2ae0]
8: /opt/xserver/bin/X (miSpriteGetImage+0x173) [0x57d2b3]
9: /opt/xserver/bin/X (compGetImage+0xb0) [0x4c9930]
10: /opt/xserver/bin/X (ProcGetImage+0x55a) [0x43a81a]
11: /opt/xserver/bin/X (Dispatch+0x341) [0x43d6a1]
12: /opt/xserver/bin/X (main+0x3ba) [0x42c2ca]
13: /lib64/libc.so.6 (__libc_start_main+0xf5) [0x7fb902f019b5]
14: /opt/xserver/bin/X (_start+0x29) [0x42c60d]
15: ? (?+0x29) [0x29]

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Knut Petersen <knut.petersen@t-online.de>

configure.ac

@@ -308,6 +308,13 @@ AC_CHECK_HEADER([execinfo.h],[
     ])]
 )
 
+PKG_CHECK_MODULES(LIBUNWIND, libunwind, [HAVE_LIBUNWIND=yes], [HAVE_LIBUNWIND=no])
+if test "x$HAVE_LIBUNWIND" = xyes; then
+	AC_DEFINE(HAVE_LIBUNWIND, 1, [Have libunwind support])
+fi
+AM_CONDITIONAL(HAVE_LIBUNWIND, [test "x$HAVE_LIBUNWIND" = xyes])
+
+
 dnl ---------------------------------------------------------------------------
 dnl Bus options and CPU capabilities.  Replaces logic in
 dnl hw/xfree86/os-support/bus/Makefile.am, among others.
@@ -1336,7 +1343,7 @@ AC_DEFINE(BIGREQS, 1, [Support BigRequests extension])
 
 if test "x$SPECIAL_DTRACE_OBJECTS" = "xyes" ; then
   DIX_LIB='$(top_builddir)/dix/dix.O'
-  OS_LIB='$(top_builddir)/os/os.O $(SHA1_LIBS) $(DLOPEN_LIBS)'
+  OS_LIB='$(top_builddir)/os/os.O $(SHA1_LIBS) $(DLOPEN_LIBS) $(LIBUNWIND_LIBS)'
 else
   DIX_LIB='$(top_builddir)/dix/libdix.la'
   OS_LIB='$(top_builddir)/os/libos.la'

include/dix-config.h.in

@@ -60,6 +60,9 @@
 /* Has backtrace support */
 #undef HAVE_BACKTRACE
 
+/* Has libunwind support */
+#undef HAVE_LIBUNWIND
+
 /* Define to 1 if you have the <byteswap.h> header file. */
 #undef HAVE_BYTESWAP_H
 

os/Makefile.am

@@ -34,6 +34,11 @@ if XDMCP
 libos_la_SOURCES += $(XDMCP_SRCS)
 endif
 
+if HAVE_LIBUNWIND
+AM_CFLAGS += $(LIBUNWIND_CFLAGS)
+libos_la_LIBADD += $(LIBUNWIND_LIBS)
+endif
+
 EXTRA_DIST = $(SECURERPC_SRCS) $(XDMCP_SRCS)
 
 if SPECIAL_DTRACE_OBJECTS

os/backtrace.c

@@ -30,6 +30,80 @@
 #include <errno.h>
 #include <string.h>
 
+#ifdef HAVE_LIBUNWIND
+
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <dlfcn.h>
+
+void
+xorg_backtrace(void)
+{
+    unw_cursor_t cursor;
+    unw_context_t context;
+    unw_word_t off;
+    unw_proc_info_t pip;
+    int ret, i = 0;
+    char procname[256];
+    const char *filename;
+    Dl_info dlinfo;
+
+    pip.unwind_info = NULL;
+    ret = unw_getcontext(&context);
+    if (ret) {
+        ErrorFSigSafe("unw_getcontext failed: %s [%d]\n", unw_strerror(ret),
+                ret);
+        return;
+    }
+
+    ret = unw_init_local(&cursor, &context);
+    if (ret) {
+        ErrorFSigSafe("unw_init_local failed: %s [%d]\n", unw_strerror(ret),
+                ret);
+        return;
+    }
+
+    ErrorFSigSafe("\n");
+    ErrorFSigSafe("Backtrace:\n");
+    ret = unw_step(&cursor);
+    while (ret > 0) {
+        ret = unw_get_proc_info(&cursor, &pip);
+        if (ret) {
+            ErrorFSigSafe("unw_get_proc_info failed: %s [%d]\n",
+                    unw_strerror(ret), ret);
+            break;
+        }
+
+        ret = unw_get_proc_name(&cursor, procname, 256, &off);
+        if (ret && ret != -UNW_ENOMEM) {
+            if (ret != -UNW_EUNSPEC)
+                ErrorFSigSafe("unw_get_proc_name failed: %s [%d]\n",
+                        unw_strerror(ret), ret);
+            procname[0] = '?';
+            procname[1] = 0;
+        }
+
+        if (dladdr((void *)(pip.start_ip + off), &dlinfo) && dlinfo.dli_fname &&
+                *dlinfo.dli_fname)
+            filename = dlinfo.dli_fname;
+        else
+            filename = "?";
+
+        ErrorFSigSafe("%u: %s (%s%s+0x%x) [%p]\n", i++, filename, procname,
+            ret == -UNW_ENOMEM ? "..." : "", (int)off,
+            (void *)(pip.start_ip + off));
+
+        ret = unw_step(&cursor);
+        if (ret < 0)
+            ErrorFSigSafe("unw_step failed: %s [%d]\n", unw_strerror(ret), ret);
+    }
+    ErrorFSigSafe("\n");
+}
+#else /* HAVE_LIBUNWIND */
 #ifdef HAVE_BACKTRACE
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
@@ -246,3 +320,4 @@ xorg_backtrace(void)
 
 #endif
 #endif
+#endif