[PATCH] os: use libunwind to generate backtraces

[Marcin Slusarz]

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

Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
---
 configure.ac            |  7 +++++
 include/dix-config.h.in |  3 +++
 os/Makefile.am          |  5 ++++
 os/backtrace.c          | 70 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 85 insertions(+)

diff --git a/configure.ac b/configure.ac
index 9415a54..4a292da 100644
--- a/configure.ac
+++ b/configure.ac
@@ -309,6 +309,13 @@ 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.
diff --git a/include/dix-config.h.in b/include/dix-config.h.in
index 578f249..5102263 100644
--- a/include/dix-config.h.in
+++ b/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
 
diff --git a/os/Makefile.am b/os/Makefile.am
index 8891485..364b6da 100644
--- a/os/Makefile.am
+++ b/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
diff --git a/os/backtrace.c b/os/backtrace.c
index daac60c..02aeb03 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -30,6 +30,75 @@
 #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: %d\n", ret);
+        return;
+    }
+
+    ret = unw_init_local(&cursor, &context);
+    if (ret) {
+        ErrorFSigSafe("unw_init_local: %d\n", 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: %d\n", 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: %d\n", 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: %d\n", ret);
+    }
+    ErrorFSigSafe("\n");
+}
+#else
 #ifdef HAVE_BACKTRACE
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
@@ -246,3 +315,4 @@ xorg_backtrace(void)
 
 #endif
 #endif
+#endif
-- 
1.8.1