PowerPC: fix backtrace to handle signal trampolines

This patch fixes backtrace for PPC32 and PPC64 to correctly handle
signal trampolines. The 'debug/tst-backtrace6.c' also check for
SA_SIGINFO handling, where is triggers another vDSO symbols for PPC32.

1 files changed, 35 insertions, 1 deletions

diff --git a/sysdeps/powerpc/powerpc64/backtrace.c b/sysdeps/powerpc/powerpc64/backtrace.c
index 2d3e051cb9..9b9a9f19da 100644
--- a/sysdeps/powerpc/powerpc64/backtrace.c
+++ b/sysdeps/powerpc/powerpc64/backtrace.c
@@ -18,6 +18,9 @@
 
 #include <execinfo.h>
 #include <stddef.h>
+#include <string.h>
+#include <signal.h>
+#include <bits/libc-vdso.h>
 
 /* This is the stack layout we see with every stack frame.
    Note that every routine is required by the ABI to lay out the stack
@@ -38,6 +41,27 @@ struct layout
   void *return_address;
 };
 
+/* Since the signal handler is just like any other function it needs to
+   save/restore its LR and it will save it into callers stack frame.
+   Since a signal handler doesn't have a caller, the kernel creates a
+   dummy frame to make it look like it has a caller.  */
+struct signal_frame_64 {
+#define SIGNAL_FRAMESIZE 128
+  char            dummy[SIGNAL_FRAMESIZE];
+  struct ucontext uc;
+  /* We don't care about the rest, since the IP value is at 'uc' field.  */
+};
+
+static inline int
+is_sigtramp_address (unsigned long nip)
+{
+#ifdef SHARED
+  if (nip == (unsigned long)__vdso_sigtramp_rt64)
+    return 1;
+#endif
+  return 0;
+}
+
 int
 __backtrace (void **array, int size)
 {
@@ -53,7 +77,17 @@ __backtrace (void **array, int size)
   for (				count = 0;
        current != NULL && 	count < size;
        current = current->next, count++)
-    array[count] = current->return_address;
+    {
+      array[count] = current->return_address;
+
+      /* Check if the symbol is the signal trampoline and get the interrupted
+       * symbol address from the trampoline saved area.  */
+      if (is_sigtramp_address ((unsigned long)current->return_address))
+        {
+	  struct signal_frame_64 *sigframe = (struct signal_frame_64*) current;
+          array[++count] = (void*)sigframe->uc.uc_mcontext.gp_regs[PT_NIP];
+	}
+    }
 
   /* It's possible the second-last stack frame can't return
      (that is, it's __libc_start_main), in which case